Organic chemistry. Cheat sheet: briefly, the most important

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Organic chemistry. Cheat sheet: briefly, the most important

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Table of contents

Bioorganic chemistry
Isomers
Related systems
Mesomeric effect
Bronsted acids
Alcohols
Chemical properties of alcohols
Polyhydric alcohols
Limit (saturated) hydrocarbons
National and international nomenclature
The concept of conformations
Natural sources of saturated hydrocarbons
Oil refining
Cracking process, ozocerite
Interaction of hydrocarbon limits with halogens
Unsaturated (unsaturated) hydrocarbons
Isomerism, natural sources and methods for producing olefins
Dehydration of primary alcohols, physical and mechanical properties of olefins
Markovnikov's rules. Wagner Method
Olefin polymerization
diene hydrocarbons
Conjugation of dienes
Rubber
Alkyns
Physical properties of alkynes
Acyclic hydrocarbons
Cyclohexane, methane, terpenes
General properties of terpenes
aromatic hydrocarbons
Nomenclature and isomerism of aromatic hydrocarbons
Production of aromatic hydrocarbons. natural springs
Synthesis, physical and chemical properties of aromatic hydrocarbons
Orientation rules in the benzene nucleus
Substitution rules in the benzene ring
Naphthalene group
Anthracene group, phenanthrene
Non-benzene aromatic compounds
Aromatic systems with a seven-membered ring
Monatomic phenols
Chemical properties of phenols
Individual representatives of phenols
Phenol-formaldehyde resins
Diatomic phenols
Trihydric phenols
Aldehydes
Methods for obtaining aldehydes
Chemical properties of aldehydes
Addition of hydrogen, water, alcohol, hydrocyanic acid, hydrosulfite
Addition of fuchsine sulphurous acid to aldehydes, polymerization of aldehydes
Individual representatives of aldehydes
Rongalite, acetalhyd, glyoxol
ketones
Chemical properties of ketones
Separate representatives of ketones
Quinones
Hydrocarbons

1. Bioorganic chemistry

This is a science that studies the biological function of organic substances in the body. It originated in the second half of the XNUMXth century. The objects of its study are biopolymers, bioregulators and individual metabolites.

Biopolymers are high-molecular natural compounds that are the basis of all organisms. These are peptides, proteins, polysaccharides, nucleic acids (NA), lipids.

Bioregulators are compounds that chemically regulate metabolism. These are vitamins, hormones, antibiotics, alkaloids, drugs, etc.

Knowledge of the structure and properties of biopolymers and bioregulators makes it possible to understand the essence of biological processes. Thus, the establishment of the structure of proteins and NA made it possible to develop ideas about the matrix protein biosynthesis and the role of NA in the preservation and transmission of genetic information.

The main task of bioorganic chemistry is to elucidate the relationship between the structure and mechanism of action of compounds.

This is the science that studies the compounds of carbon. Currently, there are 16 million organic substances.

Reasons for the diversity of organic substances.

1. Compounds of carbon atoms (C) with each other and other elements of the periodic system of D. I. Mendeleev. In this case, chains and cycles are formed.

2. A carbon atom can be in three different hybrid states. Tetrahedral configuration of the C atom → planar configuration of the C atom.

3. Homology is the existence of substances with similar properties, where each member of the homologous series differs from the previous one by a group - CH₂-.

4. Isomerism is the existence of substances that have the same qualitative and quantitative composition, but a different structure.

AM Butlerov (1861) created the theory of the structure of organic compounds, which to this day serves as the scientific basis of organic chemistry. The main provisions of the theory of the structure of organic compounds:

1) atoms in molecules are connected to each other by chemical bonds in accordance with their valency;

2) atoms in the molecules of organic compounds are interconnected in a certain sequence, which determines the chemical structure of the molecule;

3) the properties of organic compounds depend not only on the number and nature of their constituent atoms, but also on the chemical structure of the molecules;

4) in molecules there is a mutual influence of both connected and unrelated atoms directly with each other;

5) the chemical structure of a substance can be determined as a result of studying its chemical transformations and, conversely, its properties can be characterized by the structure of a substance.

2. Isomers

Spatial isomers are divided into two types: conformational and configurational.

1. Conformational isomers are called, the forms of molecules of which pass into each other due to the free rotation of atoms and groups of atoms around one or more b-bonds. The first compound for which the existence of conformational isomers is known is ethane. Its structure in space is represented by a perspective formula or Newman's formula.

2. Configuration isomers. These are stereoisomers, the molecules of which have a different arrangement of atoms in space without taking into account conformations.

Rheoisomers are divided into enantiomers and diastereomers.

Enantomers (optical isomers, antipodes mirror isomers) are stereoisomers, the molecules of which are related to each other, like an object and a mirror image incompatible with it. This phenomenon is called enantiomerism.

All chemical and physical properties of enantiomers are the same, except for two: rotation of the plane of polarized light (in a polarimeter device) and biological activity.

Enantiomerism terms:

1) the C atom is in the state of sp3 hybridization;

2) the absence of any symmetry;

3) the presence of an asymmetric (chiral) atom C, an atom having four different substituents.

Many hydroxy and amino acids have the ability to rotate the plane of polarization of a light beam to the left or right. This phenomenon is called optical 2b activity, and the molecules themselves are optically active. The deviation of the light beam to the right is marked with a "+" sign, to the left - "-" and indicate the angle of rotation in degrees.

The absolute configuration of molecules is determined by complex physicochemical methods.

The relative configuration of optically active compounds is determined by comparison with a glyceraldehyde standard. Optically active substances having the configuration of dextrorotatory or levorotatory glyceraldehyde (M. Rozanov, 1906) are called substances of the D- and L-series. An equal mixture of right and left isomers of one compound is called a racemate and is optically inactive.

Enantiomers are depicted using Fisher's formulas. Among the enantiomers, there may be symmetrical molecules that do not have optical activity, which are called mesoisomers. Optical isomers that are not mirror isomers, differing in the configuration of several, but not all, asymmetric C atoms, with different physical and chemical properties, are called s-dia-stereo-isomers.

p-diastereomers (geometric isomers) are stereomers that have a p-bond in the molecule. They are found in alkenes, unsaturated higher carboxylic acids, unsaturated dicarboxylic acids. The biological activity of organic substances is related to their structure.

3. Coupled systems

In the simplest case, conjugate systems are

These are systems with alternating double and single bonds. They can be open and closed. An open system exists in diene hydrocarbons (HC).

All C atoms are in a state of sp hybridization. Four non-hybrid p-orbits, overlapping each other, form a single electronic system. This type of conjugation is called p, p-conjugation.

There is a conjugation of p-electrons with S-electrons. This type of conjugation is called p, p-conjugation. A closed system exists in aromatic hydrocarbons.

Conjugation is an energetically favorable process, energy (E) is released in this case. The conjugation energy of butadiene - 1,3 is 15 kJ/mol, the conjugation energy of benzene is 228 kJ/mol.

2. Aromaticity

This is a concept that includes various properties of aromatic compounds. Aromatic conditions:

1) a flat closed cycle;

2) all C atoms are in sp2 hybridization;

3) a single conjugated system of all atoms of the cycle is formed;

4) the Hückel rule is fulfilled: 4n + 2 p-electrons participate in conjugation, where n = 1, 2, 3…

The simplest representative of aromatic hydrocarbons is benzene. It meets all four conditions of aromaticity. Hückel's rule: 4n + 2 = 6, n = 1.

Naphthalene is an aromatic compound 4n + 2 = 10, n = 2.

Pyridine is an aromatic heterocyclic compound. Mutual influence of atoms in a molecule

In 1861, the Russian scientist AM Butlerov put forward the position: "Atoms in molecules mutually influence each other." At present, this influence is transmitted in two ways: inductive and mesomeric effects.

The inductive effect is the transfer of electronic influence along the p-bond chain. It is known that the bond between atoms with different electronegativity (EO) is polarized, shifted to a more electronegative atom. This leads to the appearance of effective (real) charges (d) on the atoms. Such an electronic displacement is called inductive and is denoted by the letter "I" and the arrow "→".

δ+δ-

SN₃ - CH₂ → X, X = Hal-, HO-, HS-, NH₂- Etc.

The inductive effect can be positive or negative. If the X substituent attracts chemical bond electrons more strongly than the H atom, then it exhibits - II (H) = 0. In our example, X exhibits - I.

If the X substituent attracts bond electrons weaker than the H atom, then it exhibits +I. All alkyls (R=CH₃-, C₂H₅- etc.), Men+ show +I.

4. Mesomeric effect

The mesomeric effect (conjugation effect) is the influence of a substituent transmitted through a conjugated system of p-bonds. Denoted by the letter ́ "M" and a curved arrow. The mesomeric effect can be "+" or "-". It was said above that there are two types of conjugation p, p and p, p. Classification of organic reactions Chemical reactions are processes accompanied by a change in the distribution of electrons in the outer shells of atoms of the reacting substances. As a result of the reaction, some chemical bonds are broken in the reacting molecules of substances and others are formed. The reaction goes in the direction of the formation of stable particles, i.e., those with less internal energy.

Reactions can be classified according to various criteria.

1. According to the type of breaking of chemical bonds in reacting particles (substrate and reagent). The substrate is the reactant, the reactant is the active substance. This division is conditional.

There are three types of reagents:

1) radicals (R) are neutral atoms or particles with an unpaired electron (H-, C₁-.-OH, - CH3, etc.);

2) nucleophiles (Nu - "loving nuclei") - these are particles that have an electron pair at the outer electronic level of the atom;

3) electrophiles (E - "loving electrons") - these are particles that have a lack of electrons - an unfilled valence electronic level.

In reactions, the nucleophile attacks the electron-deficient reaction center in the substrate, while the electrophile attacks the reaction center with an excess of electrons. Accordingly, they distinguish:

1) radical reactions;

2) electrophilic reactions;

3) nucleophilic reactions.

2. According to the number and nature of the initial and final products, types of reactions are distinguished:

1) substitution; they are like exchange reactions in inorganic chemistry;

2) connections;

3) cleavage (elimination) is the cleavage of two atoms or groups of atoms from neighboring carbon atoms with the formation of a p-bond between them;

4) rearrangements.

Taking into account the nature of the reagents, substitution and addition reactions can be nucleophilic, electrophilic and radical and are denoted as follows:

1) nucleophilic substitution reactions;

2) electrophilic substitution reactions;

3) radical substitution reactions;

4) electrophilic addition reactions;

5) nucleophilic addition reactions;

6) oadical addition reactions.

5. Bronsted acids

To characterize the acidity and basicity of organic compounds, the Bronsted theory is used.

The main provisions of this theory.

An acid is a particle that donates a proton (an H+ donor); a base is a particle that accepts a proton (acceptor H-).

Acidity is always characterized in the presence of bases and vice versa.

A-H (acid) + B (base) - A (conjugate base) + B-H + (conjugate acid).

Bronsted acids are divided into 4 types depending on the acid center:

1) SH-acids (thiols);

2) OH-acids (alcohols, phenols, carbolic acids);

3) NC acids (amines, amides);

4) F-CH-acids (HC).

In this row, from top to bottom, acidity decreases. The strength of an acid is determined by the stability of the resulting anion. The more stable the anion, the stronger the acid. The stability of the anion depends on the delocalization (distribution) of the "negative" charge throughout the particle (anion). The more delocalized the "negative" charge, the more stable the anion and the stronger the acid.

The charge delocalization depends on:

1) on the electronegativity (EO) of the heteroatom. The more EO of a heteroatom, the stronger the corresponding acid. For example: R-OH and R-NH₂.

Alcohols are stronger acids than amines, because EO (0) → 30(N);

2) on the polarizability of the heteroatom. The greater the polarizability of a heteroatom, the stronger the corresponding acid. For example: R-SH and R-OH.

Thiols are stronger acids than alcohols, since the S atom is more polarized than the O atom;

3) on the nature of the substituent R (its length, the presence of a conjugated system, the delocalization of the electron density).

For example: CH₃-OH, CH₃-CH₂-OH, CH₃-CH₂-CH₂-HE. The acidity is less, as the length of the radical increases.

With the same acid center, the strength of alcohols, phenols and carboxylic acids is not the same. Phenols are stronger acids than alcohols due to the p, s-conjugation (+ M) of the (-OH) group. The O-H bond is more polarized in phenols. Phenols can even interact with salts (FeC₁₃) is a qualitative reaction to phenols. Compared to alcohols containing the same R, carboxylic acids are stronger acids, since the O-H bond is significantly polarized due to the M-effect of the group> C \uXNUMXd O. In addition, the carboxylate anion is more stable than the alcohol anion due to p, s-conjugations in the carboxyl group;

4) from the introduction of substituents in the radical. EA substituents increase acidity, ED substituents decrease acidity;

5) on the nature of the solvent.

6. Alcohols

Alcohols are hydrocarbon derivatives in which one or more H atoms are replaced by an -OH group. Classification.

1. By the number of OH groups, monohydric, dihydric and polyhydric alcohols are distinguished:

SN₃ -CH₂ -OH (ethanol);

SN₂OH-CH₂OH (ethylene glycol);

SN₂OH-CHOH-CH₂OH (glycerin).

2. By the nature of R, alcohols are distinguished: saturated, unsaturated, cyclic, aromatic.

3. According to the position of the group (-OH), primary, secondary and tertiary alcohols are distinguished.

4. By the number of C atoms, low molecular weight and high molecular weight are distinguished:

SN₃(SN₂)₁₄-CH₂-OH either (C₁₆ H₃₃OH);

cetyl alcohol

SN₃-(CH₂)₂₉-CH₂HE IS WITH₃₁Н₆₃, HE).

myricyl alcohol

Cetyl palmitate - the basis of spermaceti, myricyl palmitate - is found in beeswax. Nomenclature

Trivial, rational, MN (root + ending "-ol" + Arabic numeral). isomerism

Options are possible: chain isomerism, group positions - OH, optical isomerism.

Alcohols are weak acids.

Alcohols are weak bases. Attach H + only from strong acids, but they are stronger Nu.

(-I) the effect of the (-OH) group increases the mobility of H at the adjacent carbon atom. Carbon acquires d+ (electrophilic center, SE) and becomes the center of nucleophilic attack (Nu). The C-O bond breaks more easily than H-O, so SN reactions are characteristic of alcohols. They tend to run in an acidic environment, since protonation of the oxygen atom increases the d+ of the carbon atom and makes it easier to break the bond. This type includes reactions of the formation of ethers, halogen derivatives.

The shift of the electron density from H in the radical leads to the appearance of a CH-acid center. In this case, oxidation and elimination reactions take place.

physical properties

Lower alcohols (C₁-FROM₁₂) - liquids, higher - solids.

Chemical properties

Acid-base.

Alcohols are weak amphoteric compounds.

Alcoholates are easily hydrolyzed, which proves that alcohols are weaker acids than water:

R-ONa + HOH → R-OH + NaOH.

7. Chemical properties of alcohols

The -OH group is a "poorly leaving group" (the bond is of low polarity), so most reactions are carried out in an acidic medium.

Reaction mechanism:

SN₃ -CH₂ -OH+ H+ → CH₃ -CH₂ + N₂O.

carbocation

If the reaction proceeds with hydrogen halides, then the halide ion will join: CH₃ -CH₂ + Cl → CH₃ -CH₂ CI₁.

Anions in such reactions act as nucleophiles (Nu) due to the "-" charge or lone electron pair. Anions are stronger bases and nucleophilic reagents than alcohols themselves. Therefore, in practice, alcoholates are used to obtain ethers and esters, and not the alcohols themselves. If the nucleophile is another alcohol molecule, then it attaches to the carbocation:

SN₃ -CH₂ + R-0- H → CH₃ -CH₂ -OR.

ether

Reactions E (cleavage, or elimination). These reactions compete with SN reactions.

SN₃ -CH₂ -OH + H⁺ → CH₃ -CH₂ -O - H → CH₃ -CH₂ + N₂O.

The reaction proceeds at elevated temperature and catalyst H₂SO₄.

With an excess of H₂SO₄ and a higher temperature than in the case of the ether formation reaction, the catalyst is regenerated and an alkene is formed:

SN₃ -CH₂ +HS₀₄ → CH₂ = CH₂ + H₂SO₄.

The reaction E is easier for tertiary alcohols, more difficult for secondary and primary ones, since in the latter cases less stable cations are formed. In these reactions, the rule of A. M. Zaitsev is fulfilled: "During the dehydration of alcohols, the H atom is split off from the neighboring C atom with a lower content of H atoms."

In the body, the group - OH, under the action of the enzyme, is converted into an easily leaving one by the formation of esters with H₃Ro₄.

SN₃-CH₂-OH + NO-RO₃Н₂ → CH₃-CH₂-ORO₃Н₂.

Oxidation reactions:

1. Primary and secondary alcohols are oxidized by CuO, KMnO solutions₄К₂Cr₂O₇ when heated to form the corresponding carbonyl-containing compounds.

SN₃ -CH₂ -CH₂ -OH + O → CH₃ -CH₂ -HC \uXNUMXd O + H₂O;

SN₃-HSON-CH₃ + O → CH₃-CO-CH₃ + N₂О.

2. Tertiary alcohols are difficult to oxidize.

Oxidation reactions also include dehydrogenation reactions.

SN₃ -CH₂ -OH ־ CH₃ → HC = O + H₂.

IV. The reactions characteristic of the corresponding hydrocarbons (HC) proceed along the radical (R).

SN₃-CH₂-OH + 3Br₂ → SVr₃-CH₂-OH + ZNBrg;

SN₂ = CH-CH₂-OH + Br₂- → CH₂Vg-SNVg-SN₂HE.

8. Polyhydric alcohols

These alcohols are characterized by all the reactions of monohydric alcohols, but there are a number of features.

Due to the (-I) group (-OH), polyhydric alcohols have more pronounced acidic properties.

They form alcoholates not only with alkali metals, but also with alkalis:

A qualitative reaction to dihydric and polyhydric alcohols (diol fragment) is the reaction with Cu (OH) 2 in an alkaline medium, as a result of which a complex compound of copper glycolate is formed in a solution that gives a blue color.

Reactions of polyhydric alcohols can proceed on one or all groups (-OH). They form alcoholates, ethers and esters, dehydrate, oxidize.

Nitroglycerin is a colorless oily liquid. In the form of dilute alcohol solutions (1%), it is used for angina pectoris, as it has a vasodilating effect. Nitroglycerin is a strong explosive that can explode on impact or when heated. In this case, in a small volume occupied by a liquid substance, a very large volume of gases is instantly formed, which causes a strong blast wave. Nitroglycerin is part of dynamite, gunpowder.

Representatives of pentites and hexites - xylitol and sorbitol - respectively, penta- and six-atomic alcohols with an open chain. The accumulation of (-OH) - groups leads to the appearance of a sweet taste. Xylitol and sorbitol are sugar substitutes for diabetics.

Glycerophosphates - structural fragments of phospholipids, are used as a general tonic. As a result of the action of H3PO4 on glycerol, a mixture of glycerophosphates is obtained. Glycerophosphates

Glycerophosphate of iron (III) is used for anemia, asthenia, general loss of strength. Children 0,3-0,5 g 2-3 times a day, adults 1 g 3-4 times.

Calcium glycerophosphate - with overwork, rickets, nutritional decline. Children 0,05-0,2 g per reception, adults 0,2-0,5.

1. When KHSO4 acts on glycerin and when heated, acrolein is formed.

2. During the oxidation of glycerol, a number of products are formed. With mild oxidation - glyceraldehyde and dihydroxyacetone. When oxidized under severe conditions, 1,3-dioxoacetone is formed.

9. Limit (saturated) hydrocarbons

The simplest representative of the subgroup of saturated hydrocarbons is methane (CH4). I3 of methane, all other saturated hydrocarbons can be obtained, and in this regard, all saturated hydrocarbons are often called hydrocarbons of the methane series.

To obtain other hydrocarbons from methane, methane must first be treated with chlorine. In this case, the hydrogen atom in methane is replaced by a chlorine atom and methyl chloride is obtained.

If we now act on the resulting methyl chloride with metallic sodium, then sodium will take away chlorine, and the CH groups formed₃, the so-called methyl radicals, will combine in pairs with one another due to the released valences.

The chemical resistance of saturated hydrocarbons to a number of strong reagents, such as strong acids and alkalis, includes paraffins (from Latin parum affinis - "little affinity"). The reaction will result in a saturated hydrocarbon with two carbon atoms - ethane (C₂Н₆).

If, acting on ethane with chlorine, we get ethyl chloride C₂H₅Cl₁ and then, mixing it with methyl chloride, we subtract sodium chlorine, we get the next representative of saturated hydrocarbons containing three carbon atoms - propane C₃Н₈.

As can be seen from the examples given, both reactions ultimately reduce to the replacement of a hydrogen atom in the initial hydrocarbon by a methyl group. Similarly, in two stages, the following representatives of saturated hydrocarbons can be obtained: butane C₄Н₁₀, pentane C₅Н₁₂.

These hydrocarbons represent the so-called homologous series. In such a series, each subsequent compound can be obtained from the previous one by the same chemical reactions. All compounds of the homologous series, in addition, are close in their properties. The formula of each compound differs from the formula of the previous one by the same group of CH atoms₂, which is called the homological difference. Compounds that are members of a homologous series are called homologues. Nomenclature and isomerism

Wishing to show the similarity of all saturated hydrocarbons with their ancestor methane, these hydrocarbons were given names ending in -an. As for the initial part of the names, they arose in different ways. The names of the first three homologues of methane - ethane (C₂Н₆), propane (C₃Н₈) and butane (C₄Н₁₀) - arose more or less by chance. Starting from C₅Н₁₂, the names of hydrocarbons come from the Greek (or in some cases Latin) names of numbers corresponding to the number of carbon atoms in a given compound. So, a hydrocarbon with five carbon atoms is called pentane (from the Greek penta - five); a hydrocarbon with six carbon atoms is called hexane (from the Greek hexa - "six"); a hydrocarbon with seven carbon atoms is called heptane (from the Greek hepta - "seven"), etc.

When one hydrogen atom is taken away from hydrocarbons, the residues of saturated hydrocarbons are obtained, called monovalent radicals, or sometimes simply radicals.

10. National and international nomenclature

Even in the middle of the XIX century. individual chemists tried to create such a nomenclature that would speak about the structure of the named substances; such a nomenclature is called rational. In this case, for example, the names of hydrocarbons were derived from the names of the first representative of this group of hydrocarbons. So, for a number of methane, the name of methane served as the basis for the name. For example, one of the isomers of pentane can be called dimethylethylmethane, i.e. this substance can be represented as a derivative of methane, in which two hydrogen atoms are replaced by methyl CH3 groups, and one hydrogen atom is replaced by an ethyl group C₂Н₅.

International nomenclature

Desiring to create the most rational nomenclature of organic compounds that would be accepted in all countries of the world, the largest chemists - representatives of chemical societies from different countries - gathered in 1892 in Geneva (Switzerland). At this meeting, a systematic scientific nomenclature was developed, which is now usually called the Geneva or international nomenclature.

In order to name any compound according to the Geneva nomenclature, the following rules are followed.

Considering the structural formula of the compound, the longest chain of carbon atoms is chosen and the atoms are numbered, starting from the end to which the substituent is closer (side branch).

The compound is considered according to the principles of Geneva nomenclature as a derivative of a normal hydrocarbon having the same corresponding renumbered chain.

The place of the substituent (chain branch) is indicated by a number corresponding to the number of the carbon atom at which the substituent is located, then the substituent is called, and finally the hydrocarbon from which the entire compound is produced along the longest renumbered chain.

In cases where there are several branches in the chain, the position of each is indicated separately by the corresponding numbers, and each substituent is named separately. If the compound has several identical substituents, for example, two methyl groups, then after two digits denoting their places, they say "dimethyl" (from the Greek di - "two"); in the presence of three methyl groups, they say "tri-methyl", etc.

After the creation of the Geneva nomenclature, they repeatedly tried to improve it - to supplement, correct it. Thus, in Liege (Belgium) the "Liège Rules" were considered, which, however, were not accepted by many chemists.

In 1957, and then in 1965, the International Union of Pure and Applied Chemisty, abbreviated as IUPAC (or IUPAC), approved the rules for the nomenclature of organic compounds. These rules basically correspond to the Geneva nomenclature, but make some amendments to it. In the future, when presenting the International Nomenclature of various classes of compounds, IUPAC recommendations were also taken into account.

11. The concept of conformations

Metal and methylene groups in hydrocarbons (as well as in other compounds) can freely rotate around the single bonds connecting them, as around axes, as a result of which hydrogen atoms can occupy different spatial positions. The resulting various forms are called conformations or conformers. So, for example, ethane, due to the free rotation of methyl groups, can exist in the form of an innumerable number of conformations. The least stable conformation is the so-called eclipsed conformation, in which the hydrogen atoms of the two methyl groups are one above the other. The instability of this conformation is due to the small distances between hydrogen atoms, which tend to repel each other. When these atoms are repelled, the eclipsed conformation of ethane passes into others and, finally, turns into the most stable conformation, in which the hydrogen atoms of one methyl group are as far as possible from the hydrogen atoms of the other methyl group. This conformation is called hindered, because during the free rotation of methyl groups, the methane molecule spends the longest time in this conformation.

Hydrocarbons and other organic compounds containing four or more carbon atoms can be in various conformations, having not only different positions of hydrogen atoms, but also different shapes of the carbon chain. For example, the n-butane chain may have a zigzag or half ring shape.

Conformers differ from isomers primarily in that they form spontaneously, without breaking the chemical bonds connecting the atoms.

It is practically impossible to isolate any one conformation, since the rotation of atomic groups occurs rather quickly and one conformation passes into another. It was possible to draw up sufficiently accurate representations of conformations only with the help of subtle physical methods, such as, for example, the NMR method (Nuclear Magnetic Resonance).

General formula of saturated hydrocarbons. In organic chemistry, the composition of each group of compounds can be expressed by a general molecular formula.

Derivation of the general formula of saturated hydrocarbons. We need to consider the formula of any hydrocarbon with a straight chain. As can be seen from the formula, there are two hydrogen atoms for each carbon atom, except for the two hydrogen atoms associated with the extreme carbon atoms. If we denote the number of carbon atoms in a hydrocarbon molecule by the letter N, then the number of hydrogen atoms will be equal to 2N, to which 2 more must be added (third hydrogen atoms at the extreme carbon atoms). Thus, the general formula of saturated hydrocarbons Spn₂P + 2.

The derived general formula of SPN₂P + 2 will also express the composition of all branched-chain saturated hydrocarbons, since iso compounds differ from the corresponding normal compounds only in the order of connection of atoms.

The general formula of monovalent radicals of saturated hydrocarbons - alkyls - SpN₂P + 1.

12. Natural sources of saturated hydrocarbons

In nature, gaseous, liquid and solid hydrocarbons are widespread, in most cases they occur not in the form of pure compounds, but in the form of various, sometimes very complex mixtures. These are natural gases, oil and mountain wax.

Natural gaseous mixtures of hydrocarbons. In very many places on the globe, combustible, so-called earth or oil gas, consisting mainly of methane, is emitted from cracks in the earth. In Russia, such gas fields are available in Grozny, Dagestan, Saratov, the Tyumen region and other places. Petroleum gas released directly from the ground, in addition to methane, contains gasoline vapors, which can be released from it. Natural gas, along with that obtained from oil, serves as a raw material for the synthetic materials industry.

"Swamp" and "mine" gases, consisting almost exclusively of methane, are also natural sources of saturated hydrocarbons. They are formed from various plant organic residues that undergo slow decomposition with a lack of oxygen (for example, at the bottom of swamps).

Oil

Oil is a yellow or light brown to black liquid with a characteristic odor, consisting mainly of a mixture of hydrocarbons; The composition of oil also includes a small amount of substances containing oxygen, sulfur and nitrogen.

Oil is lighter than water: the density of various types of oil ranges from 0,73 to 0,97 cm³.

Depending on the field, oil has a different composition (both qualitative and quantitative). Most saturated hydrocarbons are found in oil produced in the state of Pennsylvania (USA).

Origin of oil. There is no consensus on the origin of oil. Some scientists, to whom D. I. Mendeleev belonged, assumed that oil was of inorganic origin: it arose under the action of water on metal carbides. Other scientists, such as Engler, believed that oil was of organic origin, that is, it was formed as a result of the slow decomposition of various remains of dead animals and the remains of dead plants with insufficient air access. In subsequent years, various porphyrins were found in numerous oil samples - compounds formed during the decomposition of the green substance of plants - chlorophyll and the coloring substance of blood - hemoglobin. This proves the participation of plants and animals in the formation of oil.

More complex theories are being put forward, according to which the main source of oil formation was the remains of animals and plants; the "primary oil" formed from them underwent further secondary changes, consisting mainly in the addition of hydrogen - hydrogenation. These processes could proceed with the participation of inorganic catalysts.

13. Oil refining

If the oil is gradually heated in the distillation apparatus, then at first it passes into a vaporous state as the temperature rises, hydrocarbons are distilled, having a higher and higher boiling point. In this way, individual parts or, as they say, fractions of oil can be collected. Usually three main fractions are obtained, such as:

1) the fraction collected up to 150 °C and referred to as the gasoline fraction, or the gasoline fraction; this fraction contains hydrocarbons with the number of carbon atoms from 5 to 9;

2) the fraction collected in the range from 150 to 300 °C and after purification giving kerosene contains hydrocarbons from C₉Н₂₀ to C₁₆Н₃₄;

3) oil residue, called fuel oil, contains hydrocarbons with a large number of carbon atoms - up to many tens.

Each of these three fractions undergoes a more thorough distillation to obtain fractions of a less complex composition. So, the gasoline fraction is dispersed to:

1) n-pentane, boiling at 38°C (found mainly in Pennsylvania oil);

2) gasoline, or petroleum ether (fraction with a boiling point of 40 to 70 ° C);

3) gasoline itself (fraction with a boiling point of 70 to 120 °C); there are several types of gasoline: aviation, automobile, etc.;

4) naphtha (from 120 to 140 °C).

Fuel oil is divided into fractions, some fractions that are distilled from fuel oil without decomposition above at a temperature of 300 ° C are called solar oils. They are used as motor fuel. Vaseline oil, which is used in medicine, is also obtained from solar oil by thorough purification.

In order to avoid decomposition of substances at temperatures above 300 ° C, when separating fuel oil into fractions, steam distillation and vacuum distillation are used. From fuel oil, by such separation and purification of fractions, in addition to solar oils, various lubricating oils, petroleum jelly and paraffin are obtained.

Vaseline, obtained from fuel oil by distillation with superheated water vapor, is a mixture of liquid and solid hydrocarbons and is widely used in medicine as the basis for ointments.

Paraffin - a mixture of solid hydrocarbons - is separated by their crystallization from the so-called paraffin mass - a mixture of solid and liquid hydrocarbons, which are obtained by steam distillation of fuel oil from certain types of oil rich in the corresponding solid hydrocarbons. Paraffin is currently widely used not only in industry, but also in medicine (paraffin therapy). The residue after distillation of the mentioned fractions from fuel oil, called tar or petroleum pitch, after some processing, is widely used in road construction (petroleum or artificial asphalt).

14. Cracking process, ozokerite

Cracking process (from the English cracking - "splitting"). The essence of the cracking process, or cracking of heavy fractions of oil, is that oil products are exposed to high temperature and pressure. Large molecules of hydrocarbons with a large number of carbon atoms are split into smaller molecules of saturated and unsaturated hydrocarbons, identical or close to those contained in gasoline, and cracking gases, consisting mainly of gaseous unsaturated hydrocarbons with a small number of carbon atoms. Cracking gases are subjected to additional processing, in which molecules are combined into larger ones (polymerization occurs), which also results in gasoline. Cracking of petroleum products with the polymerization of cracking off-gases increases the yield of gasoline from crude oil to 65-70%, i.e., approximately 3 times.

Mountain wax, or ozocerite, is a solid natural mixture of hydrocarbons. By melting and refining ozokerite, ceresin is prepared, which in some cases serves as a good substitute for wax.

Natural sources of saturated hydrocarbons are also some products of dry distillation of wood, peat, brown and black coal, oil shale.

Synthetic methods for obtaining saturated hydrocarbons.

1. Addition of hydrogen (hydrogenation) in the presence of catalysts - platinum and palladium - to unsaturated hydrocarbons.

2. The reaction of the removal of halogen from monohalogen derivatives using metallic sodium with the combination of radicals (Wurtz reaction).

3. Decomposition of salts of the corresponding acids (by heating with NaOH):

C&H₂n + 1 COONa + NaOH - "CnH₂n+2+Na₂CO₃.

physical properties

Limit hydrocarbons with the number of carbon atoms from 1 to 4 under normal conditions are gases; hydrocarbons with the number of atoms from 5 to 15 - liquids; hydrocarbons with 16 or more atoms are solids. The melting and boiling points of hydrocarbons increase with the enlargement of the molecules. Here one can clearly see the manifestation of the law of dialectics about the transition of quantity into quality.

Limit hydrocarbons are practically insoluble in water; they are soluble in most organic solvents.

The first representatives of a number of saturated hydrocarbons - methane and ethane - do not have a smell. Highly volatile lower hydrocarbons have the smell of gasoline. The highest representatives of this series, which are part of petroleum oils and paraffin, are also odorless, having very low volatility.

Chemical properties

At the beginning of the chapter, it was already indicated that saturated hydrocarbons under normal conditions have a high chemical inertness.

15. Interaction of limits of hydrocarbons with halogens

Halogens do not join saturated hydrocarbons. However, they enter into substitution reactions with them, especially easily in sunlight. In this case, not one, but several hydrogen atoms can be successively replaced by a halogen. So, methane, interacting with chlorine, can give several different substitution products:

SN₄ + C → CH₃CI₁ + HCI₁;

methyl chloride

SN₃CI + C₁₂ → CH₂CI₁₂ + HCI₁ etc.

methylene chloride

Hydrocarbons in which one or more hydrogen atoms are replaced by a halogen are called halogen derivatives.

Saturated hydrocarbons are less stable at high temperatures, especially in the presence of various catalysts.

Oxidation of saturated hydrocarbons at elevated temperature. The first representatives of the methane series are most difficult to oxidize; however, the highest saturated hydrocarbons, which are part of the paraffin, can be oxidized with oxygen already at 100-160 ° C to form fatty acids. In addition to fatty acids, many other substances containing oxygen are also obtained from hydrocarbons by oxidizing saturated hydrocarbons by various methods.

Splitting of the carbon chain of saturated hydrocarbons at high temperature and pressure. At 450-550 °C, reactions of the cracking process take place. The most important of them is the reaction of splitting large molecules of saturated hydrocarbons into smaller molecules of saturated and unsaturated hydrocarbons. Individual representatives

Methane (CH₄) makes up 86-90% of "earth", "marsh" and "mine" gas; in large quantities, it is part of the "luminous" gas (approximately 35%); dissolved in oil.

Methane is formed from cellulose under the influence of microorganisms ("methane fermentation"), it is part of the intestinal gases of ruminants and humans.

Synthetic methane can be obtained in several ways, such as direct interaction of carbon and hydrogen at high temperature.

Methane has neither color nor odor. When burned, it produces an almost colorless flame with a faint blue tint.

When methane is mixed with air, an extremely dangerous explosive mixture is formed.

Methane is poorly soluble in water.

Isooctane (C₈H₁₈) (2,2,4-trimethylpentane) - a very valuable component of aviation gasoline, is considered a standard liquid fuel.

16. Unsaturated (unsaturated) hydrocarbons

Unsaturated, or unsaturated, hydrocarbons are called hydrocarbons containing fewer hydrogen atoms than saturated hydrocarbons with the same number of carbon atoms, and sharply different from the limiting ones in their ability to easily enter into various addition reactions (for example, they easily add halogens).

Depending on the hydrogen content, unsaturated hydrocarbons are divided into various subgroups, or series. The composition of compounds belonging to various subgroups is conveniently expressed by general formulas.

If the composition of saturated hydrocarbons is denoted by the general formula SpN₂n + 2, then the various series of unsaturated hydrocarbons can be expressed by the general formulas: CnH₂n, C&H₂n - 2 etc.

This course will consider only unsaturated hydrocarbons having the formula SpH₂n, - alkenes, or olefins, or hydrocarbons of the ethylene series, and having the formula SpH₂n - 2, which include diolefins, or diene hydrocarbons, as well as hydrocarbons of the acetylene series.

1. Hydrocarbons of the ethylene series, or alkenes (olefins).

Hydrocarbons of the ethylene series having the general formula SpH₂n, were named after the first simplest representative of ethylene (C₂Н₄). Another name for this group of substances - olefins - arose historically: during the initial discovery and acquaintance with ethylene, it was found that, when combined with chlorine, it forms a liquid oily substance (ethylene chloride (C₂Н₄CI₁₂)), which was the reason to call ethylene gaz olefiant (from Latin - "oil-native gas"). The name "olefins" has become more widely used in our country. Olefins are also called alkenes.

2. Structure, nomenclature and isomerism Ethylene C₂Н₄ can be obtained from ethyl chloride (C₂Н₅CI₁), taking away from it the HCI molecule₁ alkali action.

The assumption of the existence of a double bond in olefins corresponds to the main position of the theory of structure about the tetravalence of carbon and well explains the addition of halogens and other substances to two neighboring carbon atoms due to the release of valences upon breaking the double bond.

According to modern concepts, as already mentioned, the two bonds connecting two unsaturated carbon atoms are not the same: one of them is an s-bond, the other is a p-bond. The latter bond is less strong and breaks during addition reactions.

The nonequivalence of two bonds in unsaturated compounds is indicated, in particular, by a comparison of the energy of formation of single and double bonds. The energy of formation of a single bond is 340 kJ/mol, and a double bond is 615 kJ/mol. Thus, the formation of a double bond does not require twice as much energy as the formation of a single s-bond, but only 275 kJ/mol more. Naturally, less energy is expended to break the p-bond than to break the s-bond.

17. Isomerism, natural sources and methods for producing olefins

The isomerism of olefins depends on the isomerism of the carbon atom chain, that is, on whether the chain is straight or branched, and on the position of the double bond in the chain. There is also a third reason for the isomerism of olefins: a different arrangement of atoms and atomic groups in space, i.e., stereoisomerism. However, this type of isomerism will be considered further on the example of compounds with a double bond.

To indicate the place of the double bond (as well as the place of branches in the chain), according to the international nomenclature, the carbon atoms of the longest chain are numbered, starting from the end to which the double bond is closer. Thus, the two straight chain isomers of butylene will be referred to as 1-butene and 2-butene.

According to the Genevan nomenclature, the priority was given to the carbon skeleton, and the numbering in the formula of this pentene began on the left, since the branch of the carbon chain is closer to the left end of the formula. According to the nomenclature, priority is given to functional groups, so the numbering starts from the right end, which is closer to the double bond that determines the main properties (functions) of olefins.

Radical N₂C=CH- produced from ethylene is usually called vinyl; radical H₂C=CH-CH₂- derived from propylene is called allyl.

Natural sources and methods for producing olefins

Ethylene and its homologues are found in very small amounts in natural gases, as well as in oil (in a dissolved state). Olefins, as mentioned, are formed during the cracking of oil, and also in small quantities during the dry distillation of wood and coal.

Withdrawal of water from saturated alcohols is dehydration. This is one of the most common ways to obtain olefins.

Under industrial conditions, alcohol vapor at 350-500 ° C is passed over a catalyst, which is used as aluminum oxide, graphite, or some other substances.

In laboratory conditions, to obtain olefins, alcohols are heated with water-removing substances, for example, concentrated sulfuric acid, zinc chloride, etc.

When sulfuric acid is used, the water splitting reaction proceeds in two stages:

1) alcohol, when interacting with sulfuric acid, forms a so-called ester, for example, ethyl sulfuric acid is formed from ethyl alcohol;

2) ethylsulfuric acid decomposes when heated, forming olefin and sulfuric acid.

The considered reaction mechanism is not the only one, since not only sulfuric acid, but also other acids, such as hydrochloric acid, which cannot form an easily decomposing intermediate product such as ethylsulfuric acid, cause dehydration of alcohols (removal of water). It has been established that the mechanism of ethylene formation from alcohols depends to a certain extent on the structure of the alcohol.

18. Dehydration of primary alcohols, physical and mechanical properties of olefins

In the dehydration of primary alcohols (in which the carbon atom associated with the hydroxyl is connected to only one radical), the following mechanism is assumed:

1) a proton (from any acid) is attached to a free pair of electrons of an oxygen atom to form a substituted oxonium ion;

2) further, when heated, water is split off from the substituted oxonium ion, as a result of which the carbocation CH should be formed₃ -CH₂ +, but, since such an ion is very fragile, it is stabilized by the loss of a proton and the formation of a double bond. In practice, the loss of water and proton (during the dehydration of primary alcohols) occurs almost simultaneously and an olefin is formed.

Cleavage of a hydrogen halide from a halogen derivative.

To remove hydrogen halide, an alcohol solution of alkali is usually used: Physical properties

The first three representatives of a number of olefins under normal conditions are gases, starting with amylenes (C₅Н₁₀), - liquids; higher olefins, starting from C₁₉Н₃₈, are rigid bodies.

Chemical properties

All olefins are characterized by numerous addition reactions that break the double bond and turn it into a simple one.

In most cases, the first stage of the reaction is the addition of a cation (for example, H +) or a cationoid species (Br^b+: Vg^b-), and, since this stage is decisive, many reactions of this kind are considered as electrophilic addition.

1. Hydrogen addition - hydrogenation. This reaction easily occurs in the presence of catalysts such as platinum and palladium at room temperature, and in the presence of crushed nickel at elevated temperatures.

2. Addition of halogens C₁₂, Br₂, I

Chlorine is the easiest to add, the hardest.

The addition of halogens can proceed (depending on the conditions) both by the radical and by the ionic mechanism. Since the reaction is often carried out under conditions in which the ionic mechanism takes place, we should dwell on the latter.

Polarization occurs, in particular, under the influence of p-electrons; in this case, a positively charged bromine atom interacts with p-electrons of the double bond with the formation of an unstable p-complex: electrophilic addition occurs.

The complex, due to the breaking of the p-bond and the addition of a positively charged bromine ion, turns into a carbocation. The liberated bromine anion is added to the carbocation to form the final addition product.

19. Markovnikov's rules. Wagner method

V. V. Markovnikov was engaged in the study of reactions of addition to olefins and established the following pattern: in the case of addition of substances containing hydrogen to unsaturated compounds, the latter is attached to the most hydrogenated carbon atom (i.e., associated with the largest number of hydrogen atoms).

This regularity is called Markovnikov's rule.

So, when HI is added to propylene, hydrogen is attached to the extreme unsaturated carbon atom (as more hydrogenated), and iodine is attached to the middle carbon atom.

According to modern concepts, the mutual influence of atoms, as a rule, is due to a change in the distribution of the density of electron clouds that form chemical bonds.

Substitution of a hydrogen atom in ethylene with a methyl group leads to a change in the distribution of electron density, so the propylene molecule is a dipole: the first carbon atom is more electronegative than the second (associated with the methyl group).

It is clear that under the action of a hydrogen halide, for example HI, the electropositive hydrogen is attached to the negatively charged extreme unsaturated carbon atom of propylene, and the electronegative halogen atom to the second carbon atom of the propylene molecule.

Since the order of attachment is actually determined by the distribution of electron densities, Markovnikov's rule has no absolute value, exceptions to this rule are known.

Attachment to water olefins. The reaction proceeds in the presence of catalysts such as sulfuric acid, zinc chloride.

This reaction is the reverse of the reaction for producing olefins from alcohols. Markovnikov's rule is also applicable to the water addition reaction.

Oxidation of olefins. Under conditions of mild oxidation, for example, when exposed to a cold aqueous solution of KMnO₄ in an alkaline or neutral environment, the double bond of olefins is broken, and two hydroxyl groups are added to the two liberated valences - the so-called dihydric alcohols are formed.

In this case, the KMnO solution₄, giving up its oxygen, becomes colorless or (with an excess of KMnO₄) turns brown (forming MnO₄). This reaction is very often used to detect the unsaturation of a test substance. Method for Oxidation of Olefins with a Weak Solution of KMnO₄ was developed by the Russian scientist E. E. Wagner and is known in the literature as the Wagner method.

Under conditions of vigorous oxidation of olefins (for example, under the action of chromic or manganese acid), their carbon chain is completely broken at the site of the double bond, and two molecules of oxygen-containing substances (organic acids, ketones, etc.) are formed.

The study of olefin oxidation products formed during the cleavage of the molecule at the site of double bonds.

20. Polymerization of olefins

polymerization of olefins. During polymerization, successive attachment of other molecules to one molecule of the olefin occurs due to the breaking of the double bond (in one or more molecules).

When two monomer molecules are combined into one, the so-called dimers are obtained, when three molecules are combined, trimers, etc.

After World War II, polyethylene (polythene) began to be produced on a large scale.

Like all polymers with a high molecular weight - high polymers, polyethylene is a mixture of molecules of different sizes, built according to the same type - polymer homologues. Therefore, the molecular weight of high polymers can only be conditionally referred to as the average molecular weight. Typically, a solid polymer of ethylene with an average molecular weight of about 6000-12 amu is used. Polyethylene is used for the production of films, dishes, water pipes, packaging materials, etc.

Of great practical importance was the propylene polymer - polypropylene, which can be obtained similarly to polyethylene.

Polypropylene is a very strong polymer used, in particular, for the manufacture of fibers. Polypropylene fibers are used for the manufacture of ropes, nets, fabrics for various purposes.

Olefin polymerization reactions are generally very important in technology, an example is the production of gasoline from the off-gases of the cracking process.

Olefin Polymerization Reaction Mechanism The ethylene polymerization equation is a summary. As is now known, polymerization proceeds much more complicated. Polymerization can proceed by both radical and ionic mechanisms. The radical mechanism will be considered as a mechanism of greater practical importance.

Free radicals, which are formed as unstable intermediate products of the reaction, are highly active. They not only connect with each other, but also interact with whole molecules. In this case, other free radicals are formed, which act on other molecules, from which free radicals are again formed. Thus, a chain reaction occurs. The theory of chain reactions was created by the Soviet scientist Academician N. N. Semenov and the English scientist S. Hinshelwood, who worked in close contact (both scientists were awarded the Nobel Prize).

All chain reactions, including polymerization, usually begin with an initiation step in which the first free radicals are formed, followed by the main reaction chain.

In the initiation reaction, catalytically acting unstable substances are usually used, which easily give rise to free radicals.

21. Diene hydrocarbons

Diolefins, diene hydrocarbons, or dienes, are unsaturated hydrocarbons having two double bonds, with the general formula CnH₂n - 2.

The names of compounds containing a double bond are added with endings - ene, but if there are two double bonds in a hydrocarbon molecule, then its name is formed with the ending - diene (from the Greek di - "two").

The two double bonds in a hydrocarbon molecule can be arranged in different ways. If they are concentrated at one carbon atom, they are called cumulated.

If two double bonds are separated by one single bond, they are called conjugated or conjugated.

If double bonds are separated by two or more simple bonds, then they are called isolated.

The position of double bonds according to the international IUPAC nomenclature is designated by the numbers of those carbon atoms from which these double bonds begin.

Dienes with cumulated and isolated double bonds have properties similar to those of olefins. Like the latter, they easily enter into numerous addition reactions.

Dienes with conjugated double bonds will be considered in more detail, since, firstly, they have important differences from olefins in some properties, and secondly, some of their representatives are of great importance as starting products for the production of synthetic rubber.

The most important feature of compounds with conjugated bonds is their higher reactivity in comparison with compounds having isolated bonds, and addition reactions to them usually proceed in a very peculiar way. So, if you act on 1,3-butadiene with chlorine, then the latter will mainly attach not to two neighboring carbon atoms that are linked by a double bond, but otherwise: chlorine atoms will attach to the ends of the chain, and instead of two double bonds, one appears in place of a simple .

An explanation for the peculiar attachment to the ends of a conjugated system of bonds is given by modern electronic concepts.

An electron diffraction study of 1,3-butadiene shows that the distances between the first and second, as well as the third and fourth carbon atoms, are somewhat larger than the distance between atoms bound by ordinary double bonds. The distance between the second and third atoms is less than the distance between atoms connected by a conventional single bond. Thus, in butadiene, the distances between carbon atoms bound by double and single bonds are, to some extent, evened out. This already shows that the single and double bonds in butadiene are somewhat different from the usual ones. The reason for the difference is that the electron clouds of two closely spaced p-bonds partially overlap each other. This is the main reason for the deviation of interatomic distances from the usual ones.

Quantum mechanics makes it possible to determine the order of bonds (P) connecting carbon atoms in butadiene.

22. Conjugation of dienes

Bond conjugation in a non-reacting molecule is called the static conjugation effect.

If a compound with a system of conjugated bonds enters into a reaction, then due to the mutual overlap of p-electron clouds at the time of the reaction, a redistribution of electron density occurs in the entire system, which is called the dynamic conjugation effect. A characteristic feature of the system of conjugated bonds is that the redistribution of electron densities for the indicated reasons is transmitted throughout the system without noticeable weakening. Therefore, when the attachment to the first atom of the conjugated system occurs, the redistribution of the electron density occurs throughout the system, and in the end, the last, fourth atom of the conjugated system, turns out to be unsaturated (and therefore attaching). Thus, conjugated double bonds are a single system that behaves similarly to a single double bond.

The second very important feature of dienes with conjugated double bonds is their extreme ease of polymerization.

Polymerization produces both cyclic and acyclic products. During the polymerization of some dienes, very long chains of compounds with rubber properties are obtained. In this case, according to the considered mechanism, both double bonds are broken in each molecule, the molecules are connected at their ends, and a double bond appears in the middle of the previously existing conjugated system.

Polymerization reactions of this type are of great importance, since they form the basis of the production of synthetic rubber.

Of the various representatives of diene hydrocarbons with conjugated double bonds, the most important are 1,3-butadiene and its homologues: 2-methyl-1,3-butadiene, or isoprene, etc.

Erythren (divinyl), or 1,3-butadiene (C₄Н₆), under normal conditions is a gas. The synthesis of divinyl on an industrial scale is carried out from alcohol according to the method of S. V. Lebedev. Alcohol vapor is passed over a heated catalyst containing aluminum oxide and zinc oxide. In this case, a number of reactions occur, of which the main one leads to the formation of divinyl, hydrogen and water.

The second important method for obtaining divinyl is the dehydrogenation of butane, which is obtained in significant quantities during oil cracking.

This method replaces the method of obtaining divinyl (and rubber) from alcohol, thereby saving valuable food products, like potatoes and wheat, which would have to be spent for the production of alcohol for industrial purposes.

Isoprene, or 2-methyl-1,3-butadiene (C₅Н₈) under normal conditions - a liquid with a boiling point of +37 ° C.

Isoprene is formed in some quantities during the dry distillation of natural rubber, which at one time served as the beginning of elucidating the structure of rubber, and then led to the development of various methods for the synthesis of artificial rubber.

23. Rubber

Rubber is of great importance, as it is widely used for the manufacture of automobile, aircraft, bicycle tubes and tires, rubber shoes, insulation of electrical wires, numerous medical products (heaters and cooling bladders, rubber probes and catheters), etc.

Rubber is obtained from the milky sap of some tropical trees. The rubber isolated from the milky juice is vulcanized, i.e., treated with sulfur or sulfur chloride, while the rubber absorbs a certain amount of sulfur, which significantly improves its quality: it becomes more elastic, acquires the ability to maintain its elasticity with significant temperature fluctuations, and also becomes more resistant to chemical influences. If a larger amount of sulfur (25-40%) is used in the vulcanization process, then a solid product will be obtained - ebonite, which is a very valuable insulating material.

Natural rubber is a polymer of isoprene (C₅Н₈)n. The number n is not a constant value; it varies greatly during the processing of rubber, and besides, as with any high polymer, this number is only an average value.

For conventional rubber used for technical purposes, the degree of polymerization, i.e., the number of monomer residues that form a polymer molecule, is approximately 400.

The synthesis of rubber consists of two major stages: the synthesis of butadiene, its homologues or any derivatives; polymerization of dienes into long chains.

The first step in the synthesis and the use of butadiene and isoprene to produce synthetic rubber has already been discussed. It should be added here that, along with the named diene hydrocarbons, a halogen derivative of butadiene, chloroprene, or 2-chloro-1,3-butadiene, turned out to be a convenient starting product for the synthesis of rubber:

Н₂C=CCI-CH=CH₂.

chloroprene

Chloroprene obtained from acetylene polymerizes, like butadiene or isoprene, into long chains of a rubbery substance having the formula (C₄Н₅CI₁). This substance is called nairite.

The second stage of rubber synthesis - the polymerization of dienes - is carried out in the presence of catalysts, for example, a small amount of metallic sodium.

Currently, a variety of synthetic rubbers are widely used, obtained by polymerization of dienes (for example, divinyl) with other unsaturated compounds: styrene C₆Н₅CH=CH₂, acrylonitrile H₂C=CH-CM, etc. This process is called copolymerization.

Many of these rubbers have valuable specific properties that distinguish them favorably from natural rubbers.

24. Alkynes

Hydrocarbons of the acetylene series having the general formula SpN₂n - 2, contain four hydrogen atoms less than the corresponding hydrocarbons of the methane series, two hydrogen atoms less than olefins, and the same amount of hydrogen as dienes, i.e., they are isomers of the latter.

1. Structure, nomenclature and isomerism

The first simplest hydrocarbon of this series is acetylene (C₂Н₂). Acetylene, like other hydrocarbons of this series, contains a triple bond. Indeed, four halogen (or hydrogen) atoms are added to acetylene, and it is easy to verify that the addition goes to both carbon atoms. Therefore, the structure of acetylene must be expressed by the formula H-C≡C-H. During the addition reaction, the triple bond is broken, each of the carbon atoms releases two valences, to which hydrogen, halogen, etc. atoms are added.

The high reactivity of the triple bond is easily explained from the standpoint of electronic representations. The electronic structure of the triple bond has already been considered. Among the three bonds connecting the carbon atoms in acetylene, one s-bond and two p-bonds. The triple bond formation energy is 840 kJ/mol, while the single bond formation energy is 340 kJ/mol. If the three bonds in the acetylene molecule were the same, then one would expect the triple bond formation energy to be 1020 kJ/mol. Therefore, the nature of the two bonds in a triple bond is different than in a single bond.

The names of the hydrocarbon series of acetylene according to the Geneva nomenclature are derived from the names of the corresponding saturated hydrocarbons, but the ending - an is replaced by the ending - in. Acetylene itself is called ethyne according to the Geneva nomenclature.

The numbering of atoms in the formula of acetylenic hydrocarbon starts from the end to which the triple bond is closer.

The place of the triple bond is indicated by a number - the number of the carbon atom from which the triple bond begins.

The isomerism of hydrocarbons of the acetylene series depends on the isomerism of the chain of carbon atoms and the position of the triple bond.

2. Methods of obtaining

A simple and widespread method for producing acetylene is from calcium carbide (CaC₂). Calcium carbide is produced on an industrial scale by heating coal in electric ovens with quicklime at a temperature of about 2500 ° C:

If calcium carbide, which is usually a solid grayish-brownish mass, is exposed to water, it rapidly decomposes with the release of gas - acetylene:

A newer production method for producing acetylene is the pyrolysis of hydrocarbons, in particular methane, which at 1400 ° C gives a mixture of acetylene with hydrogen:

2CH₄ → H - C \u3d C - H + XNUMXH₂

The general method for obtaining hydrocarbons of the acetylenic series is their synthesis from dihalogen derivatives by splitting off hydrogen halide elements with an alcoholic solution of alkali.

25. Physical properties of alkynes

Hydrocarbons from C₂Н₂ to C₄Н₆ are gases under normal conditions, starting with a hydrocarbon with five carbon atoms in a molecule - liquids, and starting with C₁₆Н₃₀ - solid bodies. The patterns in relation to the boiling and melting points in this series are the same as for the hydrocarbons of the methane series and the ethylene series.

Chemical properties

Hydrocarbons of the acetylene series are even more unsaturated than olefins. They are characterized by the following reactions.

1. Addition of hydrogen. In this reaction, as in a number of other reactions, the addition process proceeds in two stages. The reaction, as in the case of olefins, proceeds in the presence of Pt and Ni catalysts.

2. Addition of halogens. The mechanism of addition of halogens to acetylene is the same as to ethylene.

The two stages of addition of halogens to acetylene proceed at different rates: the first stage proceeds more slowly than upon addition to olefins, i.e., in practice, acetylene is halogenated more slowly than ethylene. This is explained by the smaller interatomic distance between unsaturated atoms in the acetylene molecule and the proximity of positively charged nuclei capable of repelling approaching cations.

3. Water connection. The reaction of addition of water to acetylene, proceeding under the catalytic action of mercury salts, was discovered by the Russian scientist M. G. Kucherov and is usually named after him. The reaction is of great practical importance, since acetaldehyde is used in large quantities in technology to produce acetic acid, ethyl alcohol, and a number of other substances.

4. Polymerization of acetylenic hydrocarbons. The reaction proceeds differently depending on the conditions. Thus, acetylene, when passed through a solution of CuCl and NH₄Cl₁ in hydrochloric acid at 80 °C forms vinyl-acetylene.

This reaction is of great practical importance, since vinylacetylene, easily adding HCl, turns into chloroprene.

The described addition reactions are characteristic of all unsaturated hydrocarbons, both ethylene and acetylene. However, there are reactions that are unique to acetylenic hydrocarbons and sharply distinguish them from ethylene hydrocarbons.

5. The reaction of the formation of organometallic compounds. Hydrogen atoms standing at carbon atoms connected by a triple bond have the ability to be replaced by a metal. If, for example, acetylene is passed through an ammonia solution of copper (I) chloride, then a red-brown precipitate of copper acetylene (copper acetylenide) is formed:

H-C≡C-H + 2CuCl₂ + 2NH₃ → Cu-С≡С-Cu + 2NH₄Cl.

26. Acyclic hydrocarbons

The name of alicyclic compounds arose due to the fact that they contain cycles, but are similar in properties to substances of the fatty series - aliphatic compounds. Alicyclic compounds do not contain aromatic bonds characteristic of benzene derivatives.

An exceptionally large role in the study of alicyclic compounds belongs to Russian scientists. The founder of the chemistry of alicyclic compounds is VV Markovnikov.

A large group of hydrocarbons of the alicyclic series is a cycle consisting of several methylene groups; these hydrocarbons are called polymethylene. The second large group of alicyclic hydrocarbons are derivatives of mentane, to which terpenes are close.

Polymethylene hydrocarbons, or cycloalkanes

Polymethylene hydrocarbons are composed of several methylene groups (CH₂), have the general formula SpN₂ n, i.e., are isomeric to olefins. Polymethylene hydrocarbons are also called cycloparaffins, since they, having a cyclic structure, in most cases have properties similar to paraffins. Very often, these hydrocarbons, at the suggestion of V. V. Markovnikov, are also called naphthenes (which is associated with the isolation of a number of their representatives from oil).

Individual representatives

Individual representatives of polymethylene hydrocarbons are usually named after the corresponding saturated fatty hydrocarbons with the prefix cyclo-. Thus, the simplest polymethylene hydrocarbon C₃Н₆ called cyclopropane; hydrocarbon C₄Н₈ - cyclobutane, hydrocarbon C₅Н₁₀ - cyclopentane, etc. Production methods

Cycloparaffins such as cyclopentane and cyclohexane and their substituted alkyls are found in large quantities in some types of oil, for example, in Caucasian oil. In addition, there are a number of methods for their synthetic preparation, for example, the elimination of two halogen atoms from halogen derivatives of fatty hydrocarbons containing halogen atoms at the corresponding different atoms.

Physical and chemical properties

Cyclopropane and cyclobutane at ordinary temperature are gases, cyclopentane and cyclooctane are liquids, the highest representatives are solids.

The chemical properties of cycloparaffins are similar to paraffins. These are quite chemically stable substances that enter into substitution reactions with halogens. The exception is the first two representatives - cyclopropane and cyclobutane. These substances, especially cyclopropane, behave like unsaturated fatty compounds - they are able to add halogens with ring rupture and the formation of fatty dihalogen derivatives. Differences in the behavior of cyclopropane and cyclobutane and other representatives of cycloparaffins are explained by the Bayer stress theory.

27. Cyclohexane, methane, terpenes

Cyclohexane (C₆Н₁₂) has a very close relationship to the aromatic hydrocarbon benzene, from which it can be easily obtained by hydrogenation:

С₆Н₆ + 6H → C₆Н₁₂.

In this regard, cyclohexane is often called hexahydrobenzene, considering it as a hydroaromatic compound.

Hydroaromatic compounds are those resulting from the complete or partial hydrogenation of the benzene ring in aromatic compounds.

Cyclohexane is found in significant amounts in Caucasian oil. As N. D. Zelinsky showed, cyclohexane at 300 ° C in the presence of palladium black (finely crushed palladium) dehydrogenates, turning into benzene:

С₆Н₁₂ → C₆Н₆ + 6H.

This reaction underlies the process of aromatization of oil, which is of great national economic importance.

When oxidized with nitric acid, the cyclohexane ring breaks, and adipic acid is formed:

HOOS-(CH₂)₄ -COOH.

Mentan, terpenes

Menthane, or p-methylisopropylcyclohexane, can be thought of as fully hydrogenated cymene, or p-methylisopropylbenzene.

Menthane is not found in nature, but is obtained synthetically by the hydrogenation of cymene.

To facilitate the notation of the numerous derivatives of menthane, the carbon atoms in its formula are numbered as shown.

Terpenes are a group of hydrocarbons having the general formula C₁₀Н₁₆ and similar in structure to menta-well and cymol. Terpenes differ from menthane in a lower hydrogen content (i.e., they have unsaturation), and from cymene in a high hydrogen content (i.e., they are hydrogenated, although not completely, derivatives of cymene).

Thus, terpenes occupy an intermediate position between cymene, an aromatic substance, and menthane, a fully hydrogenated derivative of cymene: C₁₀Н₁₄- cymol, C₁₀Н₁₆ - terpenes, C₁₀Н₂₀ - menthan.

Terpenes are found naturally in the sap and resin of conifers, as well as in many essential oils of a number of plants. Essential oils are obtained from various parts of plants, with the best essential oils being obtained from flowers. Various methods are used to obtain essential oils; most often they are distilled off with water vapor, less often they are extracted with organic solvents; there are other ways to get it. Essential oils, along with terpenes, contain a wide variety of substances related to alcohols, aldehydes, ketones and other groups of organic compounds.

28. General properties of terpenes

All terpenes are liquids. Being incompletely hydrogenated derivatives of cymene, they contain double bonds (one or two) in their molecules and therefore are capable of adding bromine, hydrogen chloride, etc. An important property of terpenes is their ability to be oxidized by atmospheric oxygen. The process of terpene oxidation is very complex and proceeds differently in dry and humid air. In dry air, peroxide compounds are formed, which then give up their oxygen, turning into oxide compounds. The oxidizing properties of long-standing ozonated turpentine, based on the presence of peroxide compounds in it, were used earlier when such turpentine was used as an antidote, for example, in case of phosphorus poisoning.

Terpenes, depending on the structure, are divided into several groups, of which the most important are monocyclic and bicyclic terpenes.

Monocyclic terpenes

Monocyclic terpenes contain one ring per molecule. They attach four bromine atoms, that is, they have two double bonds. Limonene can serve as a representative of monocyclic terpenes.

Limonene has one double bond in the core - between the first and second carbon atoms - the second - in the side three-carbon chain. Limonene is found in many essential oils, in particular lemon oil. The pleasant smell of lemons depends on the limonene found in the essential oil of lemons; hence the name "limonene".

Limonene is also found in the essential oils of some coniferous plants, such as the essential oil of pine needles. When distilled with steam, pine and fir needles get "forest water" - a liquid with a pleasant aromatic odor. Bicyclic terpenes

Bicyclic terpenes contain two rings per molecule. Their molecules attach two bromine atoms, therefore, bicyclic terpenes have one double bond.

Various groups of bicyclic terpenes are usually derived from hydrocarbons that do not contain double bonds - caran, pinan and camphan, which, in addition to the six-membered ring, contain three-, four- and five-membered rings. Accordingly, bicyclic terpenes of the caran, pinan, and camphan groups are distinguished.

A close examination of the formulas of bicyclic terpenes shows that the isopropyl group H takes part in the construction of their smaller ring.₃C-C-CH₃, which is also found in menthan.

The most important of the bicyclic terpenes is pinene, which belongs to the pinane group.

Pinene is the main component of turpentines, or turpentine oils, obtained from coniferous plants. The name "pinene" comes from the Latin name pinus - pine.

29. Aromatic hydrocarbons

The name "aromatic compounds" arose in the early stages of the development of organic chemistry. The group of aromatic compounds included a number of substances obtained from natural resins, balms and essential oils with a pleasant smell. Subsequently, it turned out that a number of these compounds are based on the hydrocarbon core of benzene C6 H6. In this regard, all compounds that are derivatives of benzene began to be called aromatic compounds. A huge number of aromatic compounds are known, of which only a very small part has a pleasant aromatic smell.

Benzene and its homologues

Just as methane is the "ancestor" of all saturated hydrocarbons, benzene is considered the "ancestor" of all aromatic hydrocarbons. Aromatic hydrocarbons are benzene and derivatives of benzene, in which one or more hydrogen atoms are replaced by radicals.

Benzene structure

For several decades, the structure of benzene has been a topic of lively scientific debate. Molecular formula of benzene C₆Н₆ as if talking about a large unsaturation of benzene, corresponding to the unsaturation of acetylene (C₂Н₂). Nevertheless, under normal conditions, benzene does not enter into addition reactions characteristic of unsaturated hydrocarbons: it does not add halogens, does not discolor KMnO solutions₄. For benzene, substitution reactions are more characteristic, generally characteristic of saturated hydrocarbons.

So, for example, hydrogen atoms in benzene are replaced by halogens:

С₆Н₆ + Vr₂ → C₆Н₅Vg + HBg.

bromobenzene

An important step in elucidating the structure of benzene was the theory of the cyclic structure of its molecule, put forward by A. Kekule in the 60s of the last century. Experimental data for this theory were obtained by our compatriot F. F. Beilstein and other scientists. It has been proven that monosubstituted benzenes do not have isomers. For example, there is only one bromobenzene (C₆Н₅Br), one nitrobenzene (C₆Н₅NO₂) etc.

If the carbon atoms in benzene were connected in the form of an open chain, then there would be at least three isomers of monosubstituted benzene, these isomers would differ in the position of the substituent (for example, bromine) at the first, second or third carbon atom.

It is quite clear that if the carbon atoms in benzene are linked in the form of a cycle, then there is no "beginning" of the chain, all carbon atoms are equivalent, and mono-substituted benzene cannot have isomers.

The cyclic structure of benzene was recognized by most chemists, but the question of the valence of carbon atoms and the nature of their bonds with each other was still a matter of controversy. In the cyclic formula, each carbon atom has a free fourth valence. Since stable compounds with free valences are unknown, it was necessary to assume that the fourth valences of all six carbon atoms are somehow saturated with each other.

30. Nomenclature and isomerism of aromatic hydrocarbons

Nomenclature. Rational names for aromatic hydrocarbons are usually derived from the name "benzene", adding the name of one or more radicals that replace hydrogen atoms in the benzene molecule. So, hydrocarbon C₆Н₈SN₃ called methyl benzene; hydrocarbon C₆Н₄(SN₃)(FROM₂Н₅) - methyl-ethylbenzene, etc.

Along with this method of naming, another is sometimes used: the benzene homologue is considered as a derivative of a fatty hydrocarbon in which the hydrogen atom is replaced by a benzene residue C₆Н₅which is called phenyl. Then hydrocarbon C₆Н₅-CH₃ by this method is called phenylmethane.

Some benzene homologues that are widely used in practice have well-established empirical names. For example, methylbenzene C₆Н₅-CH₃ called toluene; dimethylbenzene - C₆Н₄(SN₃)₂ - xylene, etc.

The residues of aromatic hydrocarbons, their radicals, bear the general name of aryls, by analogy with the name of fatty hydrocarbon residues - alkyls.

Isomerism. In a number of aromatic compounds, one often encounters isomerism, depending on the arrangement of two or more substituents relative to each other. So, in a disubstituted benzene molecule, two substituents can be in different positions, giving three isomers:

1) substituents can be located at neighboring carbon atoms: isomers with this arrangement are called orthoisomers;

2) substituents can be located at carbon atoms separated by one more carbon atom - metaisomers;

3) substituents can be located at carbon atoms separated by two carbon atoms, that is, located diagonally - paraisomers. For trisubstituted benzene, three different substituent arrangements are also possible:

1) all three substituents can be located at three neighboring carbon atoms; an isomer with such an arrangement of substituents is called ordinary or vicinal;

2) three substituents can be located in such a way that two of them are located at neighboring carbon atoms, and the third is in a meta position with respect to one of them; such an isomer is called unsymmetrical;

3) all three substituents can be located in the meta position one to one; such an arrangement is called symmetrical.

In addition to the considered isomerism, which depends on the location of the substituents in the ring, there can be other types of isomerism in the group of aromatic hydrocarbons. For example, radicals replacing hydrogen atoms in the benzene ring may have a straight chain of carbon atoms and a chain that is more or less branched. Further, isomerism may depend on the number of radicals containing for different isomers in total with the benzene residue the same number of carbon and hydrogen atoms.

31. Obtaining aromatic hydrocarbons. natural springs

Dry distillation of coal.

Aromatic hydrocarbons are obtained mainly from the dry distillation of coal. When coal is heated in retorts or coking ovens without air access at 1000-1300 °C, the organic substances of coal decompose with the formation of solid, liquid and gaseous products.

The solid product of dry distillation - coke - is a porous mass consisting of carbon mixed with ash. Coke is produced in huge quantities and consumed mainly by the metallurgical industry as a reducing agent in the production of metals (primarily iron) from ores.

The liquid products of dry distillation are black viscous tar (coal tar), and the aqueous layer containing ammonia is ammonia water. Coal tar is obtained on average 3% of the mass of the original coal. Ammonia water is one of the important sources of ammonia production. Gaseous products of dry distillation of coal are called coke gas. Coke oven gas has a different composition depending on the grade of coal, coking mode, etc. Coke gas produced in coke oven batteries is passed through a series of absorbers that trap tar, ammonia and light oil vapors. Light oil obtained by condensation from coke oven gas contains 60% benzene, toluene and other hydrocarbons. Most of the benzene (up to 90%) is obtained in this way and only a little - by fractionation of coal tar.

Processing of coal tar. Coal tar has the appearance of a black resinous mass with a characteristic odor. Currently, more than 120 different products have been isolated from coal tar. Among them are aromatic hydrocarbons, as well as aromatic oxygen-containing substances of an acidic nature (phenols), nitrogen-containing substances of a basic nature (pyridine, quinoline), substances containing sulfur (thiophene), etc.

Coal tar is subjected to fractional distillation, as a result of which several fractions are obtained.

Light oil contains benzene, toluene, xylenes and some other hydrocarbons.

Medium, or carbolic, oil contains a number of phenols.

Heavy, or creosote, oil: Of the hydrocarbons in heavy oil, naphthalene is contained.

Production of hydrocarbons from oil

Oil is one of the main sources of aromatic hydrocarbons. Most oils contain only very small amounts of aromatic hydrocarbons. From domestic oil rich in aromatic hydrocarbons is the oil of the Ural (Perm) field. The oil of "Second Baku" contains up to 60% of aromatic hydrocarbons.

Due to the scarcity of aromatic hydrocarbons, "oil flavoring" is now used: oil products are heated at a temperature of about 700 ° C, as a result of which 15-18% of aromatic hydrocarbons can be obtained from the decomposition products of oil.

32. Synthesis, physical and chemical properties of aromatic hydrocarbons

1. Synthesis from aromatic hydrocarbons and halogen derivatives of the fatty series in the presence of catalysts (Friedel-Crafts synthesis).

2. Synthesis from salts of aromatic acids.

When dry salts of aromatic acids are heated with soda lime, the salts decompose to form hydrocarbons. This method is similar to the production of fatty hydrocarbons.

3. Synthesis from acetylene. This reaction is of interest as an example of the synthesis of benzene from fatty hydrocarbons.

When acetylene is passed through a heated catalyst (at 500 °C), the triple bonds of acetylene are broken and three of its molecules polymerize into one benzene molecule.

physical properties

Aromatic hydrocarbons are liquids or solids with a characteristic odor. Hydrocarbons with no more than one benzene ring in their molecules are lighter than water. Aromatic hydrocarbons are slightly soluble in water.

The IR spectra of aromatic hydrocarbons are primarily characterized by three regions:

1) about 3000cm^-1, due to C-H stretching vibrations;

2) area 1600-1500cm^-1, associated with skeletal vibrations of aromatic carbon-carbon bonds and significantly varying in the position of the peaks depending on the structure;

3) area below 900cm^-1, relating to the bending vibrations of C-H of the aromatic ring.

Chemical properties

The most important general chemical properties of aromatic hydrocarbons are their tendency to substitution reactions and the high strength of the benzene ring.

Benzene homologues have a benzene core and a side chain in their molecule, for example, in hydrocarbon C₆Н₅-FROM₂Н₅ group C₆Н₅ is the benzene nucleus, and C₂Н₅ - side chain. The properties of the benzene nucleus in the molecules of benzene homologues approach the properties of benzene itself. The properties of the side chains, which are residues of fatty hydrocarbons, approach the properties of fatty hydrocarbons.

The reactions of benzene hydrocarbons can be divided into four groups.

33. Orientation rules in the benzene nucleus

When studying substitution reactions in the benzene nucleus, it was found that if the benzene nucleus already contains any substituent group, then the second group enters a certain position depending on the nature of the first substituent. Thus, each substituent in the benzene nucleus has a certain directing, or orienting, action.

The position of the newly introduced substituent is also influenced by the nature of the substituent itself, i.e., the electrophilic or nucleophilic nature of the active reagent. The vast majority of the most important substitution reactions in the benzene ring are electrophilic substitution reactions (replacement of a hydrogen atom split off in the form of a proton by a positively charged particle) - halogenation, sulfonation, nitration reactions, etc.

All substitutes are divided into two groups according to the nature of their guiding action.

1. Substituents of the first kind in electrophilic substitution reactions direct subsequent introduced groups to the ortho and para positions.

Substituents of this kind include, for example, the following groups, arranged in descending order of their directing power: -NH₂, -OH, -CH3.

2. Substituents of the second kind in electrophilic substitution reactions direct subsequent introduced groups to the meta position.

Substituents of this genus include the following groups, arranged in descending order of their directing power: -NO₂, -C≡N, -SO₃H.

Substituents of the first kind contain single bonds; substituents of the second kind are characterized by the presence of double or triple bonds.

Substituents of the first kind in the overwhelming majority of cases facilitate substitution reactions. For example, to nitrate benzene, you need to heat it with a mixture of concentrated nitric and sulfuric acids, while phenol C₆Н₅OH can be successfully nitrated with dilute nitric acid at room temperature to form ortho- and paranitrophenol.

Substituents of the second kind generally hinder substitution reactions altogether. Substitution in the ortho and para positions is especially difficult, and substitution in the meta position is relatively easier.

Currently, the influence of substituents is explained by the fact that substituents of the first kind are electron-donating (donating electrons), i.e., their electron clouds are shifted towards the benzene nucleus, which increases the reactivity of hydrogen atoms.

An increase in the reactivity of hydrogen atoms in the ring facilitates the course of electrophilic substitution reactions. So, for example, in the presence of hydroxyl, the free electrons of the oxygen atom are shifted towards the ring, which increases the electron density in the ring, and the electron density of carbon atoms in the ortho and para positions to the substituent especially increases.

34. Substitution rules in the benzene nucleus

The rules of substitution in the benzene ring are of great practical importance, since they make it possible to predict the course of the reaction and choose the correct path for the synthesis of one or another desired substance.

The mechanism of electrophilic substitution reactions in the aromatic series. Modern research methods have made it possible to largely elucidate the mechanism of substitution in the aromatic series. Interestingly, in many respects, especially at the first stages, the mechanism of electrophilic substitution in the aromatic series turned out to be similar to the mechanism of electrophilic addition in the fatty series.

The first step in electrophilic substitution is (as in electrophilic addition) the formation of a p-complex. The electrophilic particle Xd+ binds to all six p-electrons of the benzene ring.

The second stage is the formation of the p-complex. In this case, the electrophilic particle "draws" two electrons from six p-electrons to form an ordinary covalent bond. The resulting p-complex no longer has an aromatic structure: it is an unstable carbocation in which four p-electrons in a delocalized state are distributed between five carbon atoms, while the sixth carbon atom passes into a saturated state. The introduced substituent X and the hydrogen atom are in a plane perpendicular to the plane of the six-membered ring. The S-complex is an intermediate whose formation and structure have been proven by a number of methods, in particular by spectroscopy.

The third stage of electrophilic substitution is the stabilization of the S-complex, which is achieved by the elimination of a hydrogen atom in the form of a proton. The two electrons involved in the formation of the C-H bond, after the removal of a proton, together with four delocalized electrons of five carbon atoms, give the usual stable aromatic structure of substituted benzene. The role of the catalyst (usually A₁Cl₃) in this process consists in strengthening the polarization of haloalkyl with the formation of a positively charged particle, which enters into the electrophilic substitution reaction.

Addition reactions

Benzene hydrocarbons enter into the addition reaction with great difficulty - they do not discolor bromine water and KMnO solution₄. However, under special conditions, addition reactions are still possible.

1. Addition of halogens.

Oxygen in this reaction plays the role of a negative catalyst: in its presence, the reaction does not proceed. Hydrogen addition in the presence of a catalyst:

C₆H₆ + 3H₂ →C₆H₁₂

2. Oxidation of aromatic hydrocarbons.

Benzene itself is exceptionally resistant to oxidation - more resistant than paraffins. Under the action of energetic oxidizing agents (KMnO4 in an acidic medium, etc.) on benzene homologues, the benzene core is not oxidized, while the side chains undergo oxidation with the formation of aromatic acids.

35. Naphthalene group

The ancestor of the compounds of the naphthalene group is the hydrocarbon naphthalene C10 H8. The molecular formula of naphthalene was first established by A. A. Voskresensky.

The structure of naphthalene is very similar to that of benzene. X-ray studies show that the naphthalene molecule is flat, like the benzene molecule, but the interatomic distances are not as aligned as in the benzene molecule, and range from 1,356 to 1,425 A.

Isomerism of naphthalene derivatives

Monosubstituted benzenes do not have isomers. The situation is different with monosubstituted naphthalene. There are two carbon atoms in the naphthalene molecule, belonging simultaneously to both benzene nuclei; of the remaining eight carbons of naphthalene, four are bonded directly to common carbons—these four carbons are usually denoted by the letter A. The remaining four carbons are separated from the two common carbons by a-atoms; removed carbon atoms are denoted by the letter b.

In this regard, each monosubstituted naphthalene can exist in the form of a- and b-isomer, depending on which of the carbon atoms has been replaced.

Getting naphthalene

The main source of naphthalene production is coal tar containing 8-10% naphthalene. When fractionating coal tar, naphthalene passes, together with phenols, mainly into the fraction of carbolic oil. Phenols are separated from naphthalene using alkali that dissolves phenols, then naphthalene is purified by vacuum distillation and sublimation. Naphthalene in the form of its many derivatives is widely used for the manufacture of dyes, drugs, explosives, solvents, etc. Physical properties

Naphthalene is a solid crystalline substance with a characteristic odor; volatile and flammable. Naphthalene is insoluble in water, but soluble in hot alcohol, ether, and benzene. Chemical properties

Naphthalene, similar to benzene in its structure, has an aromatic character, i.e., it is easily nitrated, sulfonated, etc.

1. Addition of hydrogen (hydrogenation). Hydrogen can be added to the double bonds of naphthalene. Depending on the hydrogenation conditions, dihydronaphthalene, tetrahydronaphthalene and decahydronaphthalene are obtained. Naphthalene reduction products - tetralin and decalin - are widely used in technology as solvents, fuels, etc.

2. Substitution of hydrogen atoms.

Hydrogen atoms in naphthalene are easily replaced, and in most cases a-derivatives are more easily obtained. In many cases b-derivatives are obtained in a longer way.

3. Oxidation.

Vigorous oxidation of naphthalene or more easily occurring oxidation of its oxy- and amino derivatives leads to the formation of naphthoquinones.

36. Anthracene, phenanthrene group

Anthracene and phenanthrene having the same molecular formula C₁₄Н₁₀, contained in coal tar; they are isolated from the anthracene oil fraction.

Anthracene is a combination of three six-membered rings. The study of anthracene using X-ray diffraction analysis shows that all 14 carbon atoms of the anthracene molecule lie in the same plane. It is a crystalline substance, highly soluble in hot benzene, poorly soluble in alcohol and ether, and insoluble in water. Particularly mobile in the anthracene molecule are hydrogen atoms in positions 9 and 10, i.e., in the middle, so-called mesoposition.

The mobility of hydrogen atoms in the mesoposition is manifested, in particular, in the fact that, under the action of oxidizing agents, they are oxidized much more easily than other atoms with the formation of anthraquinone.

The most important of the anthracene derivatives are anthraquinone and alizarin.

The phenanthrene group and other condensed systems

Phenantrene is an isomer of anthracene (C₁₄Н₁₀,) is a condensed system consisting of three six-membered rings.

To designate phenanthrene derivatives, its atoms in the formula are numbered as shown above.

Phenantrene - brilliant colorless crystals, easily soluble in benzene and its homologues.

The extreme nuclei of phenanthrene have an aromatic character similar to benzene. In the middle nucleus, the 9th and 10th carbon atoms, linked by a double bond, behave like chains of unsaturated hydrocarbons, easily adding bromine (with a break in the double bond), being easily oxidized, etc.

Phenantrene has not found such a wide technical application as anthracene. However, its significance is very great. It turned out that the core of phenanthrene underlies a large number of compounds with physiological effects. So, for example, the core of phenanthren (partially hydrogenated, that is, having a smaller number of double bonds) underlies such important alkaloids as morphine and codeine.

A fully hydrogenated phenanthrene core fused to a five-membered cyclopentane ring is called cyclopentanoperhydrophenanthrene. This core underlies steroid molecules, which include sterols, D vitamins, bile acids, sex hormones, aglycones of cardiac glycosides, and a number of other biologically important substances.

Other condensed systems

Along with naphthalene, anthracene and phenanthrene, coal tar contains a large number of other hydrocarbons with condensed cycles.

Many aromatic hydrocarbons with soldered rings are carcinogenic, that is, they have the ability to cause cancer. The so-called methylcholanthrene has a particularly strong carcinogenic effect.

37. Non-benzene aromatic compounds

The main characteristic features of aromatic compounds: resistance to oxidation, ease of electrophilic substitution reactions - nitration, sulfonation, halogenation, a very low tendency to addition reactions. Of great interest are compounds that are not derivatives of benzene, but have aromatic properties, i.e., non-benzene aromatic compounds.

The works of Robinson and other researchers have shown that for the manifestation of aromatic properties, the presence in the ring (not necessarily six-membered) of the so-called aromatic sextet of electrons is necessary - six conjugated p-electrons. In order for the conjugation of p-electrons to occur, their axes must be parallel, and, therefore, the entire ring must be in the same plane - coplanar. Not all molecules can be coplanar, but those whose bond angles are close to 120° (the bond angles of benzene). Such conditions are satisfied primarily by five- and seven-membered rings. Subsequently, quantum mechanical calculations showed the possibility of the existence of a much larger number of aromatic systems, which include not only five- and seven-membered rings.

According to Hückel's rule, all rings with conjugated bonds having the number of conjugated p-electrons equal to 4n + 2 (where n = 0, 1, 2, 3, etc.) have aromatic properties. For benzene, n = 1. The number of conjugated p-electrons is 4n + 2 = 4 + 2 = 6.

Many of the non-benzene aromatic systems predicted by the theory have been synthesized.

Aromatic system with a five-membered ring

Cyclopentadienyl anion. Cyclopentadienyl anion can be obtained from cyclopentadiene, a substance belonging to the alicyclic series. The hydrogen atoms in the methylene group of this substance are highly mobile. Under the action of powdered metallic sodium in boiling xylene, hydrogen is split off from this methylene group and cyclopentadienyl sodium is formed.

In the process of splitting off a hydrogen atom and the formation of a cyclopentadienyl ion, the carbon atom has two electrons left (of which one is the own electron of carbon, and the other is from the split off hydrogen). There is a change in the hybridization of electron orbitals. Of the two remaining electrons, one in the form of a p-electron cloud overlaps with two neighboring p-electrons, forming a single conjugated system of five p-orbitals, and the other electron is evenly distributed between five p-orbitals, i.e., with the same degree of probability, it can be located on each of them. Thus, at the expense of five own electrons of carbon atoms and one extra one, a sextet of conjugated p-electrons is created, which is necessary for the manifestation of aromatic properties.

38. Aromatic systems with a seven-membered cycle

Tropilium cation. In the cyclopentadienyl anion, the aromatic sextet is created by five electrons from the carbon atoms of the five-membered ring and one extra electron. But another way of forming an aromatic sextet is also possible - with the loss of one electron from seven carbon atoms of the seven-membered ring (this is typical for the tropylium cation). The tropylium cation can be obtained by the action of molecular bromine on a hydrocarbon, tropylidene or cyclohexatriene, a seven-membered system with three double bonds.

Ultimately, the essence of the reaction is the elimination from the methylene group.

Thus, a single system of seven conjugated p-orbitals with the same C-C distances is created. However, these seven orbitals are filled with only six electrons. The lack of one electron in this system is the reason for the positive charge of the tropylium cation.

Tropilium salts are highly soluble in water and insoluble in organic solvents. Tropilium ions, which have a positive charge, easily enter into nucleophilic substitution reactions, resulting in the formation of neutral derivatives of tropylidene.

Aromatic system containing fused five-membered and seven-membered rings

Azulene. Azulene was previously presented as a condensed system containing a five-membered cyclopentadiene ring and a seven-membered cyclohexatriene ring, or a cyclopentadienocycloheptatriene system.

According to modern data, it is more correct to represent azulene as a condensed system of cyclopentadienyl anion and tropylium cation. Each of the 10 carbon atoms of azulene has a p-orbital, they all form a single electronic system. However, the electron density in the five- and seven-membered rings is not the same. Since each ring tends to have an aromatic sextet of electrons, a seven-membered ring gives up one electron to a five-membered ring. As a result, in a five-membered ring, six electrons are located in five p-orbitals (this ring will have a negative charge), and in a seven-membered ring, the remaining six electrons will be located in seven p-orbitals (this ring will have a positive charge).

Azulene is a blue crystalline substance. Azulene derivatives also have a blue or blue-violet color. The color is due to the presence of a sufficiently long conjugated system of p-electrons in the molecule.

Azulene readily isomerizes to naphthalene. Azulene derivatives, in particular, various alkyl-substituted ones, are contained in the essential oils of a number of plants, including medicinal ones (Roman chamomile, eucalyptus, some types of wormwood), which explains the anti-inflammatory effect of these plants.

39. Monatomic phenols

Methods of obtaining

1. Obtaining from coal tar. This method is the most important technical method for obtaining phenols. It consists in the fact that at first the tar fractions are treated with alkalis. Phenols, which are highly soluble in aqueous solutions of alkalis with the formation of phenolates, are easily separated from tar hydrocarbons, which, in turn, do not dissolve either in water or in aqueous solutions of alkalis. The resulting alkaline solutions are treated with sulfuric acid, which decomposes phenolates, as a result of which phenols are again released, for example:

C₆H₅ONa + H₂Total sq₄ → NaHSO₄ + C₆H₅ooh

The isolated phenols for separation are subjected to repeated fractional distillation and further purification.

2. Obtaining from salts of sulfonic acids. When salts of sulfonic acids are fused with alkalis, phenol and potassium sulfite are formed:

C₆H₅SO₃K + KOH → C₆Н₅OH + K₂Total sq₄.

The resulting phenol in the presence of KOH is converted into phenolate:

С₆Н₅OH + KOH → C₆Н₅OK+H₂О.

The phenolate is further decomposed with sulfuric acid, and free phenol is formed:

С₆Н₅OK+H₂Total sq₄ → C₆Н₅OH + KHSO₄.

3. Obtaining from cumene (isopropylbenzene).

Cumene is oxidized with atmospheric oxygen; the resulting cumene hydroperoxide under the action of sulfuric acid gives phenol and another valuable product - acetone:

cumene → cumene hydroperoxide → phenol.

4. Obtaining from diazonium salts is an important way of introducing phenolic hydroxyl.

Cumene is obtained by alkylation of benzene with propylene (separated from cracking off-gases) in the presence of catalysts (for example, AICl₁₃).

physical properties

Phenols in most cases are solid crystalline substances, very poorly soluble in water. They have a strong characteristic odour.

Chemical properties

The most important property of phenols, which distinguishes them from alcohols, is their acidity. At the same time, having a common structure with alcohols (R-OH), phenols enter into some reactions that are also characteristic of alcohols.

All phenols have slightly acidic properties, which is manifested in their ability to dissolve in alkalis with the formation of phenolate.

The acid properties of phenols are very weakly expressed. So, phenols do not stain litmus paper. The weakest inorganic acid - carbonic - displaces phenols from their salt-like compounds - phenolates:

40. Chemical properties of phenols

The formation of ethers. Phenols, like alcohols, are capable of producing compounds such as ethers. In practice, to obtain ethers of phenols, phenolates are treated with haloalkyls (1) or haloaryls (2):

C₆H₅ONa+IC₂H₅ →C₆H₅-OC₂H₅ + NaI(1)

C₆H₅ONa + BrC₆H₅ →C₆H₅-OC₆H₅ + NaBr (2)

In the first case (1), an ether is obtained containing a phenol radical and an alcohol radical, i.e., a mixed aromatic fatty ether. In the second case (2), an ether containing two phenol residues is obtained, i.e. a purely aromatic ether.

The formation of esters. Like alcohols, phenols can give compounds like esters. In practice, to obtain esters of phenols, phenolates are usually treated with acid halides. Phenols give esters with both organic and mineral acids. For example, potassium salt of phenol sulfate ester is excreted in human urine.

Staining reaction with ferric chloride. All

phenols with ferric chloride form colored compounds; monohydric phenols usually give a violet or blue color.

Substitution of hydrogen atoms in the benzene nucleus. The benzene residue in phenols affects the hydroxyl group, giving it acidic properties. However, the hydroxyl introduced into the benzene molecule also affects the benzene residue, increasing the reactivity of the hydrogen atoms in the benzene nucleus. As a result, hydrogen atoms in the core of the phenol molecule are replaced much more easily than in aromatic hydrocarbons:

1) substitution by halogens. Under the action of halogens, even bromine water, on phenols, three atoms are very easily replaced, and trihalogen-substituted phenols are obtained. Bromine atoms replace hydrogen atoms that are in the ortho and para positions with respect to the hydroxyl group. Tribromophenol is poorly soluble in water and precipitates, and therefore the reaction of its formation can serve to detect phenol;

2) substitution with the remainder of nitric acid. Phenols are very easily nitrated. Thus, under the action of even very dilute nitric acid, a mixture of nitrophenol is obtained;

3) replacement with the rest of sulfuric acid. Phenols are readily sulfonated; in this case, a mixture of o- and p-phenolsulfonic acids is obtained from phenol.

The predominance of one or another isomer depends on the temperature: at 25 °C, the orthoisomer is predominantly formed, at 100 °C, the paraisomer is formed.

Oxidation of phenols. Phenols are easily oxidized even under the action of atmospheric oxygen. At the same time, they change their color, turning into pink, red-pink or dark red. Impurities in phenols accelerate oxidation, and therefore unpurified phenols usually darken very strongly and quickly.

Antiseptic properties. Phenols kill many microorganisms, this property is used in medicine, using phenols and their derivatives as disinfectants and antiseptics. Phenol (carbolic acid) was the first antiseptic introduced into surgery by Lister in 1867. The antiseptic properties of phenols are based on their ability to fold proteins.

41. Individual representatives of phenols

Phenol, or carbolic acid, ACldum carboli-cum, C₆H₅OH is a crystalline substance with a characteristic odor, turning pink in air due to oxidation. Forms a crystalline hydrate with water₆Н₅OH, melting at 16 °C. In water, phenol dissolves in a ratio of 1: 15 (at 20 ° C). Phenol solutions with FeCl₃ give a purple color. Phenol crystals in air absorb atmospheric moisture and spread, forming a solution of water in phenol.

The use of phenol in medicine due to its toxicity is limited, and it is used only as an external agent. A large amount of phenol is used for the synthesis of dyes, picric acid, salicylic acid and other medicinal substances, as well as for the production of artificial resins - phenolic resins, such as bakelites.

Phenol ethers. The methyl and ethyl esters of phenol are called anisole and phenetol, respectively.

Both substances are liquid.

Nitrophenols. There are mono-, di- and trinitro-phenols. The introduction of a nitro group into a phenol molecule greatly increases its acidic properties: unlike phenols, nitrophenols are capable of decomposing carbonic salts, displacing carbonic acid. This property of nitrophenols is associated with their ability to exist in two tautomeric forms - benzenoid and quinoid, or aci-form.

When the aciform is formed, the hydrogen atom from the phenol hydroxyl passes to the oxygen atom in the nitro group, which is accompanied by a redistribution of chemical affinity forces. Free nitrophenols usually have a yellow color of varying intensity and shades, or are almost colorless. It depends on the quantitative ratio of two tautomeric forms of nitrophenols: a colorless benzenoid and a bright yellow aciform. This ratio depends not only on the nature of nitrophenol, but also on the concentration of hydrogen and hydroxide ions.

Due to the change in color of nitrophenols depending on the reaction of the medium, i.e., the concentration of hydrogen ions, some nitrophenols are used as indicators.

Of great importance is trinitrophenol, commonly referred to as picric acid. Picric acid can be obtained by nitration of phenol with a mixture of concentrated nitric and sulfuric acids; there are other cost-effective methods.

Like other nitrophenols, picric acid exists in two tautomeric forms.

It is a yellow crystalline substance with a bitter taste. When heated, it explodes easily. Picric acid, due to the presence of three nitric acid residues, is a fairly strong acid, approaching the degree of dissociation to mineral acids.

Picric acid is widely used as an explosive in the free state and in the form of potassium and ammonium salts, as well as a coloring agent. It is used in the treatment of burns.

42. Phenol-formaldehyde resins

The interaction of phenol with formaldehyde to form resinous products became known as early as the 1872th century. (Bayer, XNUMX). The mechanism of formation of phenol-formaldehyde resins is very complex.

During the interaction of phenol and formaldehyde, phenol alcohol is formed as the main product - o-hydroxybenzyl alcohol, or saligenin, and also, in accordance with the rules of substitution in the benzene ring, its p-isomer. The resulting o- and p-isomers condense with the release of water.

These dimers, in turn, can condense with each other, as well as with formaldehyde and phenol molecules (depending on the reaction conditions, in particular, on the amount of starting products). Ultimately, products can be formed that have a complex network structure in which hydroxyphenyl residues are linked by methylene bridges.

Phenol-formaldehyde resins used in combination with other materials (fillers) are collectively referred to as phenolic resins. These include carbolite (resin + wood flour), textolite (resin + cotton fabric), getinaks (resin + paper), fiberglass (resin + glass fiber), etc. Products made from phenolic plastics are extremely diverse: silent gears and other parts of machines, building parts, car bodies, household items, etc.

Phenol-formaldehyde resins are used as the basis of ion exchangers. Ionites or ion-exchange resins are high-molecular resins (phenol-formaldehyde, polystyrene, etc.) containing functional groups that can easily exchange their cation or anion for the corresponding ion contained in the solution. Depending on the exchanged ion, ion exchangers are divided into cation exchangers and anion exchangers. As ion-exchange groups of cations, groups are usually used - SO₃H, - COOH; in anion exchangers - groups of quaternary bases such as [Ar-NR3]OH, etc.

The use of ion exchangers is extremely diverse. When passing water containing salts successively through cation exchangers, and then anion exchangers, all salt cations are first replaced by H⁺, and then all salt anions on OH^-, i.e. desalination of water.

Ionites make it possible in scientific work and industry to isolate various organic substances from complex mixtures, for example, vitamins of group B, C. Ionites are also used to isolate alkaloids, streptomycin and other antibiotics in the factory.

Cation exchangers, giving up their hydrogen ions, replace acid catalysts, acting more gently and without requiring neutralization at the end of the process.

Ionites are also used as medicines (for example, with increased acidity of gastric juice).

43. Diatomic phenols

There are three simple dihydric phenols: o-dioxibenzene, or catechol, m-dioxibenzene, or resorcinol, p-dioxibenzene, or hydroquinone.

Some dihydric phenols are most often found in the form of derivatives in nature in plant products - tannins, resins, etc. Dihydric phenols are usually obtained synthetically by fusing salts of disulfonic acids or salts of phenol monosulfonic acids with alkalis. Dihydric phenols have properties similar to those of monohydric phenols already considered: they form phenolates, ethers and esters, and are stained with FeCl₃, give products of substitution of hydrogen atoms, etc.

However, the presence of two phenolic hydroxyls affects the properties of diatomic phenols. Thus, dihydric phenols are much more easily soluble in water than monohydric ones. Monatomic phenols are relatively easy to oxidize; in dihydric phenols, this ability is more pronounced: some dihydric phenols are oxidized so easily that they are used as reducing agents (developers) in photography (hydroquinone). Dihydric phenols are less toxic than monohydric ones. With FeCl₈ dihydric phenols give a characteristic color, which makes it possible to distinguish them by color.

Pyrocatechin, or orthodioxybenzene, is found in tannins and resins. With FeCl₈ catechol gives a green color. It oxidizes easily. So, pyrocatechin, when exposed to cold, restores silver from an ammonia solution of AgNO₃.

Adrenaline, or methylaminoethanolpyrocatechin, is produced in the adrenal glands and is a hormone that has the ability to constrict blood vessels. It is often used as a hemostatic agent. It is obtained from the adrenal glands, as well as synthetically from catechol.

Interestingly, only levorotatory (natural) adrenaline has biological activity, while dextrorotatory is biologically inactive.

Resorcinol, or m-dioxibenzene. Resorcinol can be obtained from benzene disulfonic acid by fusion with alkali.

In the presence of alkali, resorcinol is immediately converted to phenolate, which is then decomposed by acid.

With FeCl, resorcinol gives a violet color. It oxidizes fairly easily, but is much more stable than catechol. So, for example, it restores an ammonia solution of AgNO₈ only when heated, and not in the cold, like catechol. Resorcinol is much less toxic than catechol and hydroquinone, and therefore it is used in medicine as an antiseptic (for example, in the form of ointments).

Hydroquinone, or p-dioxibenzene. Under natural conditions, it occurs in some plants (for example, in the medicinal plant Uvae ursi) in the form of arbutin glucoside. In industry, hydroquinone is usually prepared by reduction of quinone.

Hydroquinone very quickly restores silver salts in the cold. Due to its high tendency to oxidize, hydroquinone is used in photography as a developer.

44. Triatomic phenols

There are three isomers of triatomic phenols, derivatives of benzene, with an ordinary, symmetrical and asymmetric arrangement of hydroxyls: pyrogallol, hydroxyhydroquinone, phloroglucinol.

The most important are triatomic phenols with an ordinary and symmetrical arrangement of hydroxyl - pyrogallol and phloroglucinum.

Pyrogallol, or p-trioxybenzene. Obtained by heating gallic acid.

With FeCl₃ pyrogallol gives a red color. Pyrogallol is very easily oxidized. For example, its alkaline solutions in air quickly turn brown due to oxidation. Pyrogallol immediately releases metallic silver from silver salts. Due to the extremely high tendency to oxidize, alkaline solutions of pyrogallol are used in gas analysis: pyrogallol absorbs oxygen from the gas mixture. Pyrogallol is also used in photography and in the synthesis of dyes.

Phloroglucinum exists in two tautomeric forms: a form with three hydroxyls and a form with three ketone groups.

Phloroglucinol oxidizes quite easily, but is much more resistant to oxidation than pyrogallol. It is used in analytical practice, for example, for the quantitative determination of pentoses: pentoses are converted into furfural, which in hydrochloric acid solution gives a colored condensation product with phloroglucinol.

Naphthols - substances similar to phenols - can be considered as products of substitution of hydroxyl for hydrogen atoms in the naphthalene core.

a-naphthol - naphthalene - b-naphthol

Naphthols can be obtained using the same reactions as phenols. One of the most important general methods for obtaining naphthols is the method of fusing sodium salts of naphthalenesulfonic acids with NaOH.

Naphthols are crystalline substances, poorly soluble in water. In terms of their chemical properties, naphthols are similar to phenols. For example, they readily dissolve in alkalis to form naphtholates. Like phenols, they react with ferric chloride solution to give colored compounds.

By reaction with FeCl8, a- and b-naphthols can be distinguished: a-naphthol gives a purple precipitate with it, and b-naphthol gives a green color and a precipitate.

Like phenols, naphthols have disinfectant properties, a-naphthol, due to its toxicity, is not used in medicine, but b-naphthol is used as a disinfectant in the treatment of intestinal diseases, a- and b-naphthols are used in large quantities in the production of dyes.

45. Aldehydes

Aldehydes are called products of substitution in hydrocarbons of a hydrogen atom by an aldehyde group - C (OH).

Ketones are substances containing a carbonyl group - C (O) - associated with two hydrocarbon residues.

Thus, both groups of compounds are characterized by the presence of a carbonyl group - C (O) -, but in aldehydes it is associated with one radical and one hydrogen atom, while in ketones the carbonyl group is associated with two radicals.

The general formula for aldehydes and ketones produced from saturated hydrocarbons is SpH2PO, and aldehydes and ketones with the same number of carbon atoms are isomeric to each other. So, for example, the formula C₃Н₆₀ have aldehyde H₃C-CH₂-C(OH) and ketone H₃ C-C(O) - CH₃.

The structure of aldehydes is expressed by the general formula R-C (O) - H.

The electronic structure of the double bond of the carbonyl group of aldehydes \uXNUMXd C \uXNUMXd O is characterized by the presence of one s-bond and one p-bond, moreover, the electron cloud of the p-bond is located in a plane perpendicular to the plane in which the s-bonds of a given carbon atom are located.

However, the double bond of the carbonyl group differs significantly from the double bond of ethylene hydrocarbons. The main difference is that the double bond of the carbonyl group connects the carbon atom to the electronegative oxygen atom, which strongly attracts electrons, so this bond is highly polarized.

The presence of a strongly polarized double bond in the carbonyl groups of aldehydes and ketones is the reason for the high reactivity of these compounds and, in particular, the reason for numerous addition reactions.

The name "aldehydes" comes from the general method for obtaining these compounds: aldehyde can be considered a product of the dehydrogenation of alcohol, i.e., the removal of hydrogen from it. The combination of two abbreviated Latin words Alcohol dehydrogenatus (dehydrogenated alcohol) gave the name aldehyde.

Depending on the nature of the radical, saturated or unsaturated aldehydes, aromatic aldehydes, etc. are distinguished.

Aldehydes are most often named after the acids they are converted to upon oxidation. So, the first representative of the aldehydes H-C (O) - H is called formic aldehyde (or formaldehyde), since during oxidation it turns into formic acid (ACldum formicum); the next homologue of CH₃ -C (O) - H is called acetaldehyde (or acetaldehyde), since when oxidized it gives acetic acid (ACldum aceticum), etc.

The simplest aromatic aldehyde C₆H5 -C (O) - H is called benzoic aldehyde or benzaldehyde, since when oxidized it gives benzoic acid (ACldum benzoicum).

According to the international nomenclature, the names of aldehydes are derived from the names of the corresponding hydrocarbons, adding to them the ending - al. So, for example, formic aldehyde is called methanal, acetic aldehyde is called ethanal, benzoic aldehyde is called phenylmethanal.

The isomerism of aldehydes is due to the isomerism of the chain of the radical.

46. Methods for obtaining aldehydes

1. Oxidation of primary alcohols is the most important way to obtain aldehydes:

1) the oxidation of alcohol with potassium dichromate is used mainly in laboratory conditions, for example, to obtain acetaldehyde;

2) oxidation of alcohol with atmospheric oxygen in the presence of metal catalysts. The most active catalyst is platinum, which acts already at room temperature. Less active, but much cheaper, is finely divided copper, which operates at high temperatures. Vapors of methyl alcohol mixed with air are sucked through the system. Methyl alcohol is oxidized with copper oxide, and the resulting metallic copper is oxidized again with atmospheric oxygen. Thus, these reactions are repeated an unlimited number of times.

The oxidation reaction of methyl alcohol with copper oxide is exothermic, i.e., it proceeds with the release of heat, so heating is necessary only at the beginning of the reaction. This method underlies the technical production of some aldehydes, such as formaldehyde.

2. From dihalogen derivatives having both halogens at the same primary carbon atom, aldehydes are obtained as a result of the reaction of nucleophilic substitution of halogens for hydroxyls. This method is used to obtain benzoic aldehyde.

physical properties

The simplest representative of the group of aldehydes - formaldehyde - under normal conditions is a gaseous substance. The next representative is acetaldehyde - a liquid boiling at 20 ° C. Subsequent representatives are also liquids. Higher aldehydes, such as palmitic aldehyde, are solids. The boiling point of aldehydes is lower than the boiling point of their corresponding alcohols. Lower aldehydes are miscible with water in any ratio, subsequent representatives are less soluble in water. Aldehydes are highly soluble in alcohol and ether. Lower aldehydes have a sharp, suffocating odor; some subsequent representatives have a more pleasant smell, reminiscent of the smell of flowers.

The carbonyl group of all carbonyl-containing compounds - aldehydes, ketones and acids - gives an intense (due to strong polarization) absorption band, and for each group of carbonyl compounds this band is in a narrow range. For formaldehyde - at 1745 cm^-1, for other aliphatic aldehydes - in the region of 1740-1720 cm^-11.

Aldehydes, as well as ketones, due to the presence of a carbonyl group =C=O, have selective absorption in ultraviolet light, giving absorption maxima in the region of 2800 A. Many aromatic aldehydes have pleasant odors.

47. Chemical properties of aldehydes

Aldehydes enter into a very large number of reactions, representing one of the most reactive groups of the compound. For the convenience of considering the reactions of aldehydes, they can be divided into groups in accordance with the atoms and groups of atoms that are present in the aldehyde molecule.

Oxidation reactions.

Aldehydes are very easily oxidized. It is especially characteristic of aldehydes that such weak oxidizing agents as some oxides and hydroxides of heavy metals, which do not act on a number of other organic compounds, easily oxidize aldehydes of free metals or their oxides (aldehyde reactions):

1) oxidation with silver oxide ("silver mirror" reaction). If an aldehyde solution is added to a transparent colorless ammoniacal solution of silver oxide and the liquid is heated, then on the walls of the test tube, with sufficient purity, a coating of metallic silver is formed in the form of a mirror; if the walls of the test tube are not clean enough, then metallic silver is released in the form of a light gray precipitate. In this case, the aldehyde is oxidized to an acid with the same number of carbon atoms as in the original aldehyde;

2) oxidation with copper hydroxide. If a solution containing aldehyde is added to a liquid with a light blue precipitate of copper hydroxide and the mixture is heated, then a yellow precipitate of copper hydroxide (I) CuOH appears instead of a blue precipitate. The aldehyde is then converted to an acid.

When heated, yellow copper (II) hydroxide turns into red copper (I) oxide:

2CuOH → Cu₂O+H₂O;

3) air oxygen oxidizes only some of the most easily oxidized aldehydes, which include aromatic aldehydes, such as benzaldehyde. If a thin layer of benzaldehyde is applied to a watch glass and left for several hours, it will turn into crystals of benzoic acid. The oxidation of benzaldehyde with atmospheric oxygen proceeds as a complex multi-stage process with the formation of free radicals and an intermediate easily decomposing peroxide-type product, the so-called perbenzoic acid;

4) the Cannizzaro reaction, or dismutation reaction, is an oxidation-reduction reaction (oxide reduction), in which one of two aldehyde molecules is oxidized to acid, while the other is reduced to alcohol. This reaction, characteristic mainly of aromatic aldehydes, was discovered in 1853 by the Italian scientist Cannizzaro, who found that in the presence of a concentrated alkali solution (for example, a 60% KOH solution), benzaldehyde is converted into a salt of benzoic acid and benzyl alcohol.

Only aldehydes that do not have a hydrogen atom at the a-carbon atom of the aldehyde enter the Cannizzaro reaction.

48. Addition of hydrogen, water, alcohol, hydrocyanic acid, hydrosulfite

Reactions of the carbonyl group:

Addition reactions to the carbonyl of aldehydes: in the course of these reactions, in most cases, the first stage is the addition to the positively charged carbon atom of the carbonyl \uXNUMXd C \uXNUMXd O of a negatively charged particle (for example, the OH anion). Therefore, many reactions of this group belong to nucleophilic addition reactions:

1) the addition of hydrogen (hydrogenation) occurs with the breaking of the double bond of the carbonyl group of the aldehyde. Aldehydes are converted to primary alcohols. Depending on the conditions, in particular on the nature of the reducing reagent, the mechanism may be different;

2) the addition of water leads to the formation of aldehyde hydrates.

The reaction mechanism is as follows: nucleophilic addition to the carbon atom of the hydroxyl anion of water occurs; then a proton joins the formed anion. Compounds with two hydroxyls on the same carbon atom are fragile: they lose a water molecule and turn into aldehydes. Therefore, the above reaction is reversible. In most cases, aldehyde hydrates exist only in aqueous solutions, and it is not possible to isolate them in the free state. Their existence is proved by physical methods, in particular, by studying infrared spectra. The binding strength in water aldehyde hydrates varies depending on the nature of the radicals in different aldehydes;

3) the addition of an alcohol to aldehydes leads to the formation of a hemiacetal. Nucleophilic addition also occurs here. Hemiacetals can be considered as partial ethers, derivatives of the hydrated form of the aldehyde. When aldehydes are heated with alcohols in the presence of traces of anhydrous HCl, acetals are formed. Acetals can be considered as full ethers, derivatives of the hydrated form of aldehydes.

Acetals are usually liquids with a pleasant odor, poorly soluble in water. They are easily hydrolyzed in the presence of acids, but are not hydrolyzed by alkalis;

4) the addition of hydrocyanic acid to aldehydes gives oxynitriles, or cyanohydrins. Nucleophilic addition occurs. Alkalis in small quantities catalyze this reaction;

5) the addition of sodium hydrosulfite (bisulfite) occurs when aldehyde solutions are shaken with a concentrated solution of sodium hydrosulfite. Hydrosulfite compounds of aldehydes are poorly soluble in a concentrated solution of sodium hydrosulfite and are precipitated. This reaction is of great practical importance.

49. Addition of fuchsulfurous acid to aldehydes, polymerization of aldehydes

The addition of fuchsulfurous acid to aldehydes underlies the characteristic staining reaction that is often used for the qualitative discovery of aldehydes. If sulfur dioxide SO is passed through a red fuchsin solution₂, then a colorless solution of the so-called fuchsine sulfuric acid, or Schiff's reagent, is obtained. When fuchsine sulfurous acid is added to an aldehyde solution, the mixture acquires a red or red-violet color. With the subsequent addition of mineral acids, this coloration, as a rule, disappears; the exception is formaldehyde; fuchsine sulphurous acid staining caused by formaldehyde does not disappear with the addition of acids.

polymerization of aldehydes. Not only a number of substances are attached to aldehydes at the place of their carbonyl group, but the aldehyde molecules themselves are able to combine with each other (with the breaking of the double bond of their carbonyl group). These reactions include polymerization and aldol condensation. In a polymerization reaction, the rest of the molecules in the polymer are often bonded through an atom of oxygen, nitrogen, or another element (not carbon). The polymerization of aldehydes is catalytically accelerated by mineral acids (H₂Total sq₄, H₂Total sq₃, HCl). As a result of this reaction, in some cases, relatively small molecules of a cyclic polymer are formed. In other cases, during polymerization, open chains of molecules of various lengths are formed. Polymerization reactions are reversible.

Aldol condensation. When small amounts of dilute alkali act on aldehydes, polymerization of aldehydes occurs, which, by the nature of the connection of the initial molecules that bind directly to their carbon atoms, is often called condensation. The product of this reaction has an aldehyde and an alcohol group, i.e., it is an aldehyde alcohol. By shortening the last term, these substances began to be called aldols, and the reaction in question was called aldol condensation. The reaction of aldol condensation is of great importance, for example, in the formation of sugary substances.

The electronic mechanism of the reaction of aldol condensation is as follows. The hydroxyl anion (catalyzing this reaction) abstracts a proton from the a-carbon (whose hydrogen atoms are highly reactive due to their proximity to the aldehyde group). The resulting strongly nucleophilic carbon anion adds to the electrophilic carbon atom of another aldehyde molecule. The resulting hydroxyaldehyde anion is stabilized by adding a proton from the water, which releases a hydroxide ion (catalyst).

50. Separate representatives of aldehydes

Formaldehyde under normal conditions is a gas with a sharp unpleasant (pungent) odor, highly soluble in water; A 40% aqueous solution of formaldehyde, called formalin, is widely used in medical practice.

In the static state of the formaldehyde solution, oxidation-reduction processes gradually take place in it. Due to dismutation, formalin usually contains methyl alcohol and formic acid along with formaldehyde. The dismutation reaction is catalyzed by alkalis.

When formalin is concentrated, as well as during long-term storage of formaldehyde, especially at low temperatures, a white precipitate of formaldehyde polymer called paraformaldehyde or simply paraform is formed in it.

nH₂C=O ↔ (N₂CO)n

The polymerization of formaldehyde can be represented as follows. Hydrated formaldehyde molecules split off water and form chains of greater or lesser length. Paraform molecules contain from three to eight molecules of formaldehyde (as A. M. Butlerov showed), and under certain conditions (at very low temperatures) - much more.

Low temperature promotes polymerization of formaldehyde and therefore formalin should not be stored below 10-12°C. At the same time, high temperature contributes to the rapid volatilization of formaldehyde from the solution. The process of depolymerization and reverse polymerization underlies paraform sublimation.

The medical use of formaldehyde is based on its ability to fold proteins. Protein substances of bacteria coagulate from formaldehyde, which causes their death. One of the most important medical applications of formaldehyde is its use for the purpose of disinfection, i.e., the destruction of pathogens. Formalin vapor (when it is boiled) is used to fumigate the disinfected premises, the hands of surgeons, surgical instruments, etc. are treated with formaldehyde solutions. Formaldehyde solutions are used to preserve (preserve) anatomical preparations. Large amounts of formaldehyde are used in the synthesis of plastics. From formaldehyde, the medical preparation hexamethylenetetramine, or urotropin, is obtained. This drug is obtained by reacting formaldehyde (or paraform) with ammonia:

6CH₂O + 4NH₃ → (CH₂)₆N₄ + 6H₂О.

The rational name "hexamethylenetetramine" was given by A. M. Butlerov in connection with the presence of six methylene groups and four nitrogen atoms in the molecule. A. M. Butlerov was the first to receive urotropin and studied it.

When a solution of urotropine is heated in the presence of acids, it hydrolyzes with the formation of the initial products - formaldehyde and ammonia:

(CH₂)₆N₄ + 6H₂O → 6CH₂O + 4NH₃.

51. Rongalite, acetalhyd, glyoxol

Rongalite, or sodium formaldehyde sulfoxylate, which is used both for the synthesis of drugs (for example, novarsenol) and in technology as a reducing agent, is also a derivative of formaldehyde. To obtain rongalite, formaldehyde is treated with sodium hydrosulfite, resulting in a hydrosulfite compound of formaldehyde. Next, the formaldehyde hydrosulfite compound is reduced with zinc dust.

Acetic aldehyde (acetaldehyde, or ethanal) on an industrial scale is usually obtained by dehydrogenation of ethyl alcohol vapor under the action of a catalyst (copper): two hydrogen atoms are split off from alcohol. An important method for obtaining acetaldehyde is also the Kucherov reaction - the addition of water to acetylene.

Under laboratory conditions, acetaldehyde is usually obtained from alcohol by oxidizing it with potassium dichromate in an acidic medium.

Acetaldehyde is a volatile liquid. In high concentrations, it has an unpleasant suffocating odor; in small concentrations, it has a pleasant smell of apples (in which it is contained in a small amount).

When a drop of acid is added to acetaldehyde at room temperature, it polymerizes into paraaldehyde; at low temperatures, acetaldehyde polymerizes into metaldehyde, a crystalline solid.

Paraldehyde is a cyclic trimer (CH₃AtoN)₃, metaldehyde - cyclic tetramer (CH₃AtoN)₄, it is sometimes used in everyday life as a fuel under the name "dry alcohol". Paraldehyde was previously used as a hypnotic.

An important derivative of acetaldehyde is trichloroacetaldehyde, or chloral. Chloral is a heavy liquid. It adds water to form a crystalline solid chloral hydrate, or chloral hydrate. Chloral hydrate is one of the very few examples of stable aldehyde hydrates. Chloral hydrate is easily (already in the cold) decomposed by alkalis with the formation of chloroform and a salt of formic acid. Chloral hydrate is used as a sleeping pill.

Glyoxal is the simplest representative of dialdehydes - compounds with two aldehyde groups.

Benzoic aldehyde, or benzaldehyde, occurs in nature in the form of amygdalin glycoside, which is found in bitter almonds, leaves of laurel cherry and bird cherry, pits of peaches, apricots, plums, etc. Under the influence of the emulsin enzyme, as well as during acid hydrolysis, amygdalin is split into hydrocyanic acid, benzaldehyde and two glucose molecules.

As an intermediate product of the hydrolysis of amygdalin, benzaldehyde cyanohydrin can be isolated, which can be considered as a product of the interaction of benzaldehyde and HCN.

In the bitter almond water Aqim amuda agit atagarum, a preparation of bitter almonds, hydrocyanic acid is found mainly in the form of benzal dehydcyanohydrin.

52. Ketones

Ketones are substances containing a carbonyl group - C (O) - associated with two radicals. The general formula of ketones is RC(O)-R'.

Radicals can be aliphatic (limiting or unsaturated), alicyclic, aromatic.

Aromatic ketones can be divided into two subgroups:

1) mixed fatty-aromatic containing one aromatic residue;

2) purely aromatic ketones containing two aromatic residues.

Nomenclature and isomerism

Usually ketones are named after the radicals included in their molecule, adding the word ketone. So, the simplest representative of H₃C-C(O) - CH₃ called dimethyl ketone, H₃C-C(O) - C₂Н₅ - methyl ethyl ketone, N₃C-C(O) - C₆Н₅ - methyl phenyl ketone, C₆H-C(O) - C₆Н₅ - diphenyl ketone, etc.

According to the international nomenclature, the names of ketones are derived from the names of the corresponding hydrocarbons, adding to this name the ending - he. So, dimethyl ketone will be called pro-panone, methyl ethyl ketone - butanone, etc.

To indicate the position of the carbonyl group, the carbon atoms are numbered, starting from the end to which the carbonyl group is closer, and, naming the ketone, the carbonyl position is indicated by the corresponding number.

Some ketones also have their own empirical names. For example, dimethyl ketone is commonly referred to as acetone, methyl phenyl ketone as acetophenone, and diphenyl ketone as benzophenone.

The isomerism of ketones depends on the position of the carbonyl group in the chain, as well as on the isomerism of the radicals. How to get

Ketones can be made in ways similar to those used to make aldehydes.

1. Oxidation of secondary alcohols.

2. Obtaining from dihalogen derivatives in which both halogen atoms are located at the same secondary carbon atom.

3. Obtaining carboxylic acids from calcium salts by their dry distillation. So, acetone is obtained from calcium acetate.

To obtain mixed ketones (with different radicals), salts of the corresponding acids containing the desired radicals are taken.

Dry distillation of wood produces some ketones, such as acetone and methyl ethyl ketone.

Aromatic ketones are conveniently prepared by the Friedel-Crafts reaction by treating a fatty or aromatic acid chloride with an aromatic hydrocarbon in the presence of aluminum chloride.

physical properties

The simplest ketone, acetone, is a liquid. Subsequent representatives are also liquids. Higher aliphatic as well as aromatic ketones are solids. The simplest ketones are miscible with water. All ketones are highly soluble in alcohol and ether. The simplest ketones have a characteristic odor.

53. Chemical properties of ketones

Ketones have a number of properties characteristic of the carbonyl group, which bring them closer to aldehydes. At the same time, ketones do not have a hydrogen atom associated with carbonyl, which is characteristic of aldehydes, and therefore do not give a number of oxidative reactions, which are very characteristic of aldehydes. Ketones are substances less reactive than aldehydes. As mentioned earlier, many addition reactions to aldehydes proceed due to the strong polarization of the carbonyl group according to the ionic mechanism.

The radicals associated with the carbonyl group have the so-called positive induction effect: they increase the electron density of the bond of the radical with other groups, i.e., as if quenching the positive charge of the carbon atom of the carbonyl.

As a result, carbonyl-containing compounds, according to the decrease in their chemical activity, can be arranged in the following row:

formaldehyde - acetaldehyde - acetone.

There is another - stereochemical - reason for the lower reactivity of ketones compared to aldehydes. The positively charged carbon atom of the carbonyl group of aldehydes is bonded to one radical and a small hydrogen atom. In ketones, this carbon atom is bonded to two radicals, both of which are often very bulky. Thus, a nucleophilic particle (OH, OR, etc.), already approaching the carbonyl group of ketones, can encounter "steric obstacles". Further, as a result of the addition of a nucleophilic particle to the carbonyl carbon and the corresponding atoms or groups of atoms to the carbonyl oxygen, the hybridization of the electrons of this carbon changes: sp₂ -sp₃. In three-dimensional space, three more or less bulky groups and a hydrogen atom should be located near the "former" carbonyl carbon of the aldehyde.

At the same time, in the case of a ketone, all 4 groups located around this carbon atom will be quite bulky.

1. Relation to oxidation: ketones are not oxidized by those weak oxidizing agents that easily oxidize aldehydes. So, for example, ketones do not give a "silver mirror reaction", are not oxidized by copper hydroxide and Fehling's solution. However, ketones can be oxidized by such strong oxidizing agents as KMn04 or chromium mixture. In this case, the carbon chain of the ketone is broken at the carbonyl group with the formation of acids with a smaller number of carbon atoms compared to the original ketone. This also distinguishes ketones from aldehydes.

The reaction of oxidative cleavage of ketones is of great importance for establishing their structure, since the position of the carbonyl group in the ketone molecule can be judged from the acids formed.

2. Reactions of the carbonyl group: a number of reactions characteristic of the carbonyl group of aldehydes proceed in exactly the same way with the ketone carbonyl group.

54. Individual representatives of ketones

Acetone (dimethyl ketone, propanone) N₃C-C(0) - CH₃ - the simplest representative of the ketone group. One of the most important sources of obtaining acetone is the dry distillation of wood. Acetone is also obtained by dry distillation of calcium acetate. A splitting similar to that of calcium acetate is also experienced by free acetic acid when its vapor is passed over heated catalysts (AI₂O₃, ThO₂ and etc.).

This reaction is also used in engineering to produce acetone. An important method for obtaining acetone is cumene. Acetone is also obtained biochemically - as a result of the so-called acetone fermentation of starch, which occurs under the influence of certain bacteria.

Acetone is a colorless liquid with a characteristic odor. Acetone is completely miscible with water. Acetone very well dissolves a number of organic substances (for example, nitrocellulose, varnishes, etc.), therefore, it is used in large quantities as a solvent (production of smokeless powder, rayon, etc.).

Acetone is the starting product for the production of a number of medicinal substances, such as iodoform. When acetone is treated with chlorine or iodine in an alkaline medium, acetone is halogenated:

The resulting triiodoacetone is extremely easily cleaved under the influence of alkali to form iodoform and an acetic acid salt.

This reaction is often used to discover acetone, considering, however, that under the same conditions iodoform is also formed from ethyl alcohol, acetaldehyde, and some other substances. A qualitative color reaction for acetone is the reaction with sodium nitroprusside Na₂[Fe (CN)₅(NO)], giving an intense wine red color with acetone.

Acetone appears in the urine in severe cases of diabetes - sugar disease. Urine at the same time acquires the smell of acetone, reminiscent of a fruity smell. To open acetone in urine, the iodoform formation reaction (Liben's test) and the staining reaction with sodium nitroprusside (Legal's test) are used.

Monohalogenated acetone - bromoacetone and chlorine acetone (СlН₂C-C(O) - CH₃) - are tear chemical warfare agents (lacri-mators).

Diacetyl (H₃C-C(O) - C(O) - CH₃) is the simplest representative of diketones. It is a yellow liquid. It has a strong smell of butter and is contained in it, causing its smell; used to impart a pleasant smell to margarine.

Camphor is a ketone, similar in carbon skeleton to terpenes. Camphor is a crystalline substance with a characteristic odor and a peculiar burning and bitter taste; very volatile and can be purified by sublimation. Camphor is insoluble in water, but readily soluble in organic solvents.

Most often, camphor is used as a heart remedy.

55. Quinones

Quinones are six-membered cyclic diketones with two double bonds.

Of these, paraquinone, obtained by the oxidation of hydroquinone or aniline, is of the greatest practical importance. Paraquinone is the starting product in the synthesis of hydroquinone. The arrangement of double bonds characteristic of quinone determines the color of a number of compounds.

Naphthoquinones are naphthalene derivatives containing a quinoid nucleus. The most important is 1,4-naphthoquinone, which can be obtained by the oxidation of naphthalene.

In a number of its properties, 1,4-naphthoquinone is similar to p-benzoquinone. It crystallizes in the form of yellow needles, is volatile, and has a sharp, irritating odor.

The core of 1,4-naphthoquinone is the basis of vitamin K, or antihemorrhagic vitamin (which prevents the appearance of hemorrhages). Vitamin K is 2-methyl-3-wick-1,4-naphthoquinone. Vitamin K is found in green herbs, leaves, and vegetables. It is a yellow oil, insoluble in water; distilled in high vacuum.

It turned out that the wick group (unsaturated alcohol residue of phytol) is not essential for the manifestation of antihemorrhagic action. A number of other 1,4-naphthoquinone derivatives have this effect, for example, 2-methyl-1,4-naphthoquinone, which is easily obtained synthetically and successfully used instead of vitamin K - usually in the form of water-soluble derivatives.

Some quinone derivatives play an important role in the intermediate processes of biological oxidation.

Anthraquinones are anthracene derivatives containing a quinoid nucleus. Anthraquinone can be easily obtained by oxidizing anthracene with nitric acid or a chromium mixture. In this case, two keto groups are formed in the molecule, and the middle ring acquires the structure of a quinone. Anthraquinone is a yellow crystalline substance, unlike conventional quinones, it is quite resistant to a number of chemical influences, in particular to oxidation.

Anthrahydroquinone is an intermediate in the reduction of anthraquinone to anthracene. An-trahydroquinone in free form is brown crystals. Having two phenolic hydroxyls, anthrahydroquinone dissolves in alkalis; the resulting phenolate-type substance has a bright red color. Anthraquinone is able to brominate, nitrate and sulfonate.

Alizarin is 1,2-dioxanthraquinone.

Emodes. In medical practice, preparations (tinctures, decoctions, etc.) from aloe, rhubarb, buckthorn, senna leaves, etc. are often used as laxatives. The active substances of these plants, as it turned out, are anthraquinone derivatives, namely, substituted di- and trihydroxy-anthraquinones, contained in plants partly in free form, partly in the form of esters and glycosides. These derivatives of di- and trihydroxyanthraquinones are often combined into the group of emodins. An example of emodins is franguloemodin, which is 3-methyl-1,6,8-trihydroxyanthraquinone. Franguloemodin is found in buckthorn (Frangula).

56. Hydrocarbons

Carbohydrates are widely distributed in nature and play a very important role in human life. They are part of the food, and usually a person's need for energy is covered when eating for the most part precisely due to carbohydrates.

The exceptional importance of this group of compounds has become particularly clear in recent years. So, the nucleic acids necessary for the biosynthesis of proteins and for the transfer of hereditary properties are built from derivatives of carbohydrates - nucleotides. Many carbohydrates play an important role in the processes that prevent blood clotting, the penetration of pathogens into macroorganisms, in strengthening immunity, etc. Carbohydrate derivatives are of great importance in the process of photosynthesis.

Some types of carbohydrates are part of the membranes of plant cells and play a mechanical, supporting role. From carbohydrates of this type, by chemical processing, a person prepares fabrics (artificial silk), explosives (nitrocellulose), etc.

Many carbohydrates and their derivatives are medicines.

The name of the substances "carbohydrates" appeared on the basis of data from the analysis of the first known representatives of this group of compounds, the substances of this group consist of carbon, hydrogen and oxygen, and the ratio of the numbers of hydrogen and oxygen atoms in them is the same as in water, i.e. for every two hydrogen atoms account for one oxygen atom. Sometimes a newer name is used - glycides; reduced general carbohydrate formula C_m(H_2nO)_n remains true for the vast majority of representatives.

A large class of carbohydrates is divided into two groups: simple and complex.

Simple carbohydrates (monosaccharides or monos) are called carbohydrates that are not able to hydrolyze to form simpler carbohydrates. Most of these substances have a composition corresponding to the general formula C_n(n_2nABOUT)_n that is, they have the same number of carbon atoms as the number of oxygen atoms.

Complex carbohydrates (polysaccharides, or polyoses) are carbohydrates that can be hydrolyzed to form simple carbohydrates. Most of these substances have a composition corresponding to the general formula C_mH_2nO_n, i.e., their number of carbon atoms is not equal to the number of oxygen atoms.

Carbohydrate-containing biopolymers - glycoproteins, glycolipids and others that perform the most complex functions in the body - have a particularly complex structure.

Authors: Drozdov A.A., Drozdova M.V.

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