Aromatic HCs (arenas) are hydrocarbons whose molecules contain one or more benzene rings.

Examples of aromatic hydrocarbons:

Benzene row arenas (monocyclic arenas)

General formula:C n H 2n-6 , n≥6

The simplest representative of aromatic hydrocarbons is benzene, its empirical formula is C 6 H 6 .

The electronic structure of the benzene molecule

The general formula of C n H 2 n -6 monocyclic arenes shows that they are unsaturated compounds.

In 1856, the German chemist A.F. Kekule proposed a cyclic formula for benzene with conjugated bonds (single and double bonds alternate) - cyclohexatriene-1,3,5:

This structure of the benzene molecule did not explain many of the properties of benzene:

• for benzene, substitution reactions are characteristic, and not addition reactions characteristic of unsaturated compounds. Addition reactions are possible, but they are more difficult than for;
• benzene does not enter into reactions that are qualitative reactions to unsaturated hydrocarbons (with bromine water and a solution of KMnO 4).

Electron diffraction studies carried out later showed that all bonds between carbon atoms in a benzene molecule have the same length of 0.140 nm (the average value between the length of a single C-C bond of 0.154 nm and a double C=C bond of 0.134 nm). The angle between the bonds at each carbon atom is 120°. The molecule is a regular flat hexagon.

Modern theory to explain the structure of the C 6 H 6 molecule uses the concept of hybridization of atomic orbitals.

The carbon atoms in benzene are in a state of sp 2 hybridization. Each "C" atom forms three σ-bonds (two with carbon atoms and one with a hydrogen atom). All σ-bonds are in the same plane:

Each carbon atom has one p-electron, which does not participate in hybridization. The unhybridized p-orbitals of carbon atoms are in a plane perpendicular to the plane of σ-bonds. Each p-cloud overlaps with two neighboring p-clouds, and as a result, a single conjugated π-system is formed (remember the effect of conjugation of p-electrons in the 1,3-butadiene molecule, discussed in the topic “Diene hydrocarbons”):

The combination of six σ-bonds with a single π-system is called aromatic bond.

A ring of six carbon atoms linked by an aromatic bond is called benzene ring, or benzene nucleus.

In accordance with modern ideas about the electronic structure of benzene, the C 6 H 6 molecule is depicted as follows:

Physical properties of benzene

Benzene under normal conditions is a colorless liquid; t o pl = 5.5 o C; t o kip. = 80 about C; has a characteristic smell; immiscible with water, good solvent, highly toxic.

Chemical properties of benzene

The aromatic bond determines the chemical properties of benzene and other aromatic hydrocarbons.

The 6π-electron system is more stable than conventional two-electron π-bonds. Therefore, addition reactions are less typical for aromatic hydrocarbons than for unsaturated hydrocarbons. The most typical for arenes are substitution reactions.

I. Substitution reactions

1.Halogenation

2. Nitration

The reaction is carried out with a mixture of and acids (nitrating mixture):

3. Sulfonation

4. Alkylation (replacement of the "H" atom by an alkyl group) - Friedel-Crafts reactions, homologues of benzene are formed:

Instead of haloalkanes, alkenes can be used (in the presence of a catalyst - AlCl 3 or inorganic acid):

II. Addition reactions

1. Hydrogenation

2. Addition of chlorine

III.Oxidation reactions

1. Combustion

2C 6 H 6 + 15O 2 → 12CO 2 + 6H 2 O

2. Incomplete oxidation (KMnO 4 or K 2 Cr 2 O 7 in an acidic environment). The benzene ring is resistant to oxidizing agents. The reaction does not occur.

Getting benzene

In industry:

1) oil and coal processing;

2) dehydrogenation of cyclohexane:

3) dehydrocyclization (aromatization) of hexane:

In the laboratory:

Fusion of salts of benzoic acid with:

Isomerism and nomenclature of benzene homologues

Any benzene homologue has a side chain, i.e. alkyl radicals attached to the benzene ring. The first homologue of benzene is a benzene nucleus linked to a methyl radical:

Toluene has no isomers, since all positions in the benzene ring are equivalent.

For subsequent homologues of benzene, one type of isomerism is possible - side chain isomerism, which can be of two types:

1) isomerism of the number and structure of substituents;

2) isomerism of the position of substituents.

Physical properties of toluene

Toluene- a colorless liquid with a characteristic odor, insoluble in water, soluble in organic solvents. Toluene is less toxic than benzene.

Chemical properties of toluene

I. Substitution reactions

1. Reactions involving the benzene ring

Methylbenzene enters into all substitution reactions in which benzene is involved, and at the same time exhibits a higher reactivity, the reactions proceed at a faster rate.

The methyl radical contained in the toluene molecule is a substituent of the genus, therefore, as a result of substitution reactions in the benzene nucleus, ortho- and para-derivatives of toluene are obtained or, with an excess of the reagent, tri-derivatives of the general formula:

a) halogenation

With further chlorination, dichloromethylbenzene and trichloromethylbenzene can be obtained:

II. Addition reactions

hydrogenation

III.Oxidation reactions

1. Combustion
C 6 H 5 CH 3 + 9O 2 → 7CO 2 + 4H 2 O

2. Incomplete oxidation

Unlike benzene, its homologues are oxidized by some oxidizing agents; in this case, the side chain undergoes oxidation, in the case of toluene, the methyl group. Mild oxidizing agents like MnO 2 oxidize it to an aldehyde group, stronger oxidizing agents (KMnO 4) cause further oxidation to an acid:

Any homologue of benzene with one side chain is oxidized by a strong oxidizing agent such as KMnO4 to benzoic acid, i.e. there is a break in the side chain with the oxidation of its cleaved off part to CO 2; For example:

In the presence of several side chains, each of them is oxidized to a carboxyl group and as a result polybasic acids are formed, for example:

Getting toluene:

In industry:

1) oil and coal processing;

2) dehydrogenation of methylcyclohexane:

3) dehydrocyclization of heptane:

In the laboratory:

1) Friedel-Crafts alkylation;

2) Wurtz-Fittig reaction(reaction of sodium with a mixture of halobenzene and haloalkane).

Arenes (aromatic hydrocarbons) – these are unsaturated (unsaturated) cyclic hydrocarbons whose molecules contain stable cyclic groups of atoms (benzene nuclei) with a closed system of conjugated bonds.

General formula: C n H 2n–6for n ≥ 6.

Chemical properties of arenes

Arenas- unsaturated hydrocarbons, the molecules of which contain three double bonds and a cycle. But due to the conjugation effect, the properties of arenes differ from those of other unsaturated hydrocarbons.

Aromatic hydrocarbons are characterized by reactions:

• accession,
• substitution,
• oxidation (for benzene homologues).

The aromatic system of benzene is resistant to oxidizing agents. However, benzene homologs are oxidized by the action of potassium permanganate and other oxidizing agents.

1. Addition reactions

Benzene adds chlorine in the light and hydrogen when heated in the presence of a catalyst.

1.1. hydrogenation

Benzene adds hydrogen when heated and under pressure in the presence of metal catalysts (Ni, Pt, etc.).

Hydrogenation of benzene produces cyclohexane:

Hydrogenation of homologues gives cycloalkane derivatives. When toluene is heated with hydrogen under pressure and in the presence of a catalyst, methylcyclohexane is formed:

1.2. Chlorination of arenes

The addition of chlorine to benzene proceeds by radical mechanism at high temperature, under the influence of ultraviolet radiation.

Chlorination of benzene in the presence of light produces 1,2,3,4,5,6-hexachlorocyclohexane (hexachloran).

Hexachloran is a pesticide used to control harmful insects. The use of hexachlorane is currently prohibited.

Benzene homologues do not add chlorine. If the benzene homologue reacts with chlorine or bromine exposed to light or high temperature (300°C), then there is a substitution of hydrogen atoms on the side alkyl substituent, not on the aromatic ring.

2. Substitution reactions

2.1. Halogenation

Benzene and its homologues enter into substitution reactions with halogens (chlorine, bromine) in the presence of catalysts (AlCl 3 , FeBr 3) .

When interacting with chlorine on the AlCl 3 catalyst, chlorobenzene is formed:

Aromatic hydrocarbons interact with bromine when heated and in the presence of a catalyst - FeBr 3 . Metallic iron can also be used as a catalyst.

Bromine reacts with iron to form iron(III) bromide, which catalyzes the bromination of benzene:

Meta-chlorotoluene is formed in small amounts.

In the interaction of benzene homologues with halogens in the light or at high temperature(300 o C), hydrogen is replaced not in the benzene ring, but in the side hydrocarbon radical.

For example, when chlorinating ethylbenzene:

2.2. Nitration

Benzene reacts with concentrated nitric acid in the presence of concentrated sulfuric acid (nitrating mixture).

In this case, nitrobenzene is formed:

Toluene reacts with concentrated nitric acid in the presence of concentrated sulfuric acid.

In the reaction products, we indicate either O-nitrotoluene:

or P-nitrotoluene:

The nitration of toluene can also proceed with the substitution of three hydrogen atoms. In this case, 2,4,6-trinitrotoluene (trotyl, tol) is formed:

2.3. Alkylation of aromatic hydrocarbons

• Arenes interact with haloalkanes in the presence of catalysts (AlCl 3, FeBr 3, etc.) to form benzene homologues.

• Aromatic hydrocarbons interact with alkenes in the presence of aluminum chloride, iron (III) bromide, phosphoric acid, etc.

• Alkylation with alcohols proceeds in the presence of concentrated sulfuric acid.

2.4. Sulfonation of aromatic hydrocarbons

Benzene reacts when heated with concentrated sulfuric acid or a solution of SO 3 in sulfuric acid (oleum) to form benzenesulfonic acid:

3. Oxidation of arenes

Benzene is resistant to even strong oxidizing agents. But benzene homologues are oxidized under the action of strong oxidizing agents. Benzene and its homologs burn.

3.1. Complete oxidation - combustion

The combustion of benzene and its homologues produces carbon dioxide and water. The combustion reaction of arenes is accompanied by the release of a large amount of heat.

2C 6 H 6 + 15O 2 → 12CO 2 + 6H 2 O + Q

The general combustion equation for arenes is:

C n H 2n–6 + (3n – 3)/2 O 2 → nCO 2 + (n – 3)H 2 O + Q

When aromatic hydrocarbons burn in a lack of oxygen, carbon monoxide CO or soot C can be formed.

Benzene and its homologues burn in air with a smoky flame. Benzene and its homologues form explosive mixtures with air and oxygen.

3.2. Ooxidation of benzene homologues

Benzene homologues are easily oxidized by permanganate and potassium dichromate in an acidic or neutral medium when heated.

At the same time, it happens oxidation of all bonds at the carbon atom adjacent to the benzene ring, except for the bond of this carbon atom to the benzene ring.

Toluene oxidizes potassium permanganate in sulfuric acid with education benzoic acid:

If toluene is oxidized in a neutral solution when heated, then it is formed salt of benzoic acid - potassium benzoate:

So toluene decolorizes acidified potassium permanganate solution when heated.

Longer radicals are oxidized to benzoic acid and carboxylic acid:

When propylbenzene is oxidized, benzoic and acetic acids are formed:

Isopropylbenzene is oxidized by potassium permanganate in an acidic environment to benzoic acid and carbon dioxide:

4. Orienting action of substituents in the benzene ring

If there are substituents in the benzene ring, not only alkyl, but also containing other atoms (hydroxyl, amino group, nitro group, etc.), then the substitution reactions of hydrogen atoms in the aromatic system proceed in a strictly defined way, in accordance with the nature influence of the substituent on the aromatic π-system.

Types of substituents on the benzene ring

Substituents of the first kind	Substituents of the second kind
ortho- and pair-position	Further substitution occurs mainly in meta-position
Electron donor, increase the electron density in the benzene ring	Electron-withdrawing, reduce the electron density in the conjugated system.
alkyl substituents: CH 3 -, C 2 H 5 - and etc.; hydroxyl, amine: –OH, –NH 2; halogens: –Cl, –Br	nitro group: – NO 2 , – SO 3 Н; carbonyl - CHO; carboxyl: - COOH, nitrile: - C≡ N; – CF3

Arenes are aromatic hydrocarbons containing one or more benzene rings. The benzene ring is made up of 6 carbon atoms, between which double and single bonds alternate.

It is important to note that the double bonds in the benzene molecule are not fixed, but constantly move in a circle.

Arenes are also called aromatic hydrocarbons. The first member of the homologous series is benzene - C 6 H 6 . The general formula for their homologous series is C n H 2n-6.

For a long time, the structural formula of benzene remained a mystery. The formula proposed by Kekule with two triple bonds could not explain the fact that benzene does not enter into addition reactions. As mentioned above, according to modern concepts, double bonds in a molecule are constantly moving, so it is more correct to draw them in the form of a ring.

Double bonds form a conjugation in the benzene molecule. All carbon atoms are in a state of sp 2 hybridization. Valence angle - 120°.

Nomenclature and isomerism of arenes

The names of arenes are formed by adding the names of substituents to the main chain - the benzene ring: benzene, methylbenzene (toluene), ethylbenzene, propylbenzene, etc. Substituents are, as usual, listed in alphabetical order. If there are several substituents in the benzene ring, then the shortest path between them is chosen.

Arenes are characterized by structural isomerism associated with the position of substituents. For example, two substituents on a benzene ring may be in different positions.

The name of the position of the substituents in the benzene ring is formed on the basis of their location relative to each other. It is denoted by the prefixes ortho-, meta- and para. Below you will find mnemonic hints for their successful memorization;)

Getting arenas

Arenas are obtained in several ways:

Chemical properties of arenes

Arenes are aromatic hydrocarbons that contain a benzene ring with conjugated double bonds. This feature makes addition reactions difficult (but still possible!)

Remember that, unlike other unsaturated compounds, benzene and its homologues do not discolor bromine water and potassium permanganate solution.

© Bellevich Yury Sergeevich 2018-2020

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DEFINITION

Benzene(cyclohexatriene - 1,3,5) - an organic substance, the simplest representative of a number of aromatic hydrocarbons.

Formula - C 6 H 6 (structural formula - Fig. 1). Molecular weight - 78, 11.

Rice. 1. Structural and spatial formulas of benzene.

All six carbon atoms in the benzene molecule are in the sp 2 hybrid state. Each carbon atom forms 3σ bonds with two other carbon atoms and one hydrogen atom lying in the same plane. Six carbon atoms form a regular hexagon (σ-skeleton of the benzene molecule). Each carbon atom has one unhybridized p-orbital, which contains one electron. Six p-electrons form a single π-electron cloud (aromatic system), which is depicted as a circle inside a six-membered cycle. The hydrocarbon radical derived from benzene is called C 6 H 5 - - phenyl (Ph-).

Chemical properties of benzene

Benzene is characterized by substitution reactions proceeding according to the electrophilic mechanism:

- halogenation (benzene interacts with chlorine and bromine in the presence of catalysts - anhydrous AlCl 3, FeCl 3, AlBr 3)

C 6 H 6 + Cl 2 \u003d C 6 H 5 -Cl + HCl;

- nitration (benzene easily reacts with a nitrating mixture - a mixture of concentrated nitric and sulfuric acids)

- alkylation with alkenes

C 6 H 6 + CH 2 \u003d CH-CH 3 → C 6 H 5 -CH (CH 3) 2;

Addition reactions to benzene lead to the destruction of the aromatic system and proceed only under harsh conditions:

- hydrogenation (the reaction proceeds when heated, the catalyst is Pt)

- addition of chlorine (occurs under the action of UV radiation with the formation of a solid product - hexachlorocyclohexane (hexachloran) - C 6 H 6 Cl 6)

Like any organic compound, benzene enters into a combustion reaction with the formation of carbon dioxide and water as reaction products (it burns with a smoky flame):

2C 6 H 6 + 15O 2 → 12CO 2 + 6H 2 O.

Physical properties of benzene

Benzene is a colorless liquid, but has a specific pungent odor. Forms an azeotropic mixture with water, mixes well with ethers, gasoline and various organic solvents. Boiling point - 80.1C, melting point - 5.5C. Toxic, carcinogen (i.e. contributes to the development of cancer).

Obtaining and using benzene

The main methods for obtaining benzene:

— dehydrocyclization of hexane (catalysts - Pt, Cr 3 O 2)

CH 3 -(CH 2) 4 -CH 3 → C 6 H 6 + 4H 2;

- dehydrogenation of cyclohexane (the reaction proceeds when heated, the catalyst is Pt)

C 6 H 12 → C 6 H 6 + 4H 2;

– trimerization of acetylene (the reaction proceeds when heated to 600C, the catalyst is activated carbon)

3HC≡CH → C 6 H 6 .

Benzene serves as a raw material for the production of homologues (ethylbenzene, cumene), cyclohexane, nitrobenzene, chlorobenzene, and other substances. Previously, benzene was used as an additive to gasoline to increase its octane number, however, now, due to its high toxicity, the content of benzene in fuel is strictly regulated. Sometimes benzene is used as a solvent.

Examples of problem solving

EXAMPLE 1

Exercise

Write down the equations with which you can carry out the following transformations: CH 4 → C 2 H 2 → C 6 H 6 → C 6 H 5 Cl.

Solution

To obtain acetylene from methane, the following reaction is used: 2CH 4 → C 2 H 2 + 3H 2 (t = 1400C). Obtaining benzene from acetylene is possible by the reaction of trimerization of acetylene, which occurs when heated (t = 600C) and in the presence of activated carbon: 3C 2 H 2 → C 6 H 6 . The chlorination reaction of benzene to obtain chlorobenzene as a product is carried out in the presence of iron (III) chloride: C 6 H 6 + Cl 2 → C 6 H 5 Cl + HCl.

EXAMPLE 2

Exercise	To 39 g of benzene in the presence of iron (III) chloride was added 1 mol of bromine water. What amount of the substance and how many grams of what products did this result in?
Solution	Let us write the equation for the reaction of benzene bromination in the presence of iron (III) chloride: C 6 H 6 + Br 2 → C 6 H 5 Br + HBr. The reaction products are bromobenzene and hydrogen bromide. The molar mass of benzene, calculated using the table of chemical elements of D.I. Mendeleev - 78 g/mol. Find the amount of benzene substance: n(C 6 H 6) = m(C 6 H 6) / M(C 6 H 6); n(C 6 H 6) = 39/78 = 0.5 mol. According to the condition of the problem, benzene reacted with 1 mol of bromine. Consequently, benzene is in short supply and further calculations will be made for benzene. According to the reaction equation n (C 6 H 6): n (C 6 H 5 Br) : n (HBr) \u003d 1: 1: 1, therefore n (C 6 H 6) \u003d n (C 6 H 5 Br) \u003d: n(HBr) = 0.5 mol. Then, the masses of bromobenzene and hydrogen bromide will be equal: m(C 6 H 5 Br) = n(C 6 H 5 Br)×M(C 6 H 5 Br); m(HBr) = n(HBr)×M(HBr). Molar masses of bromobenzene and hydrogen bromide, calculated using the table of chemical elements of D.I. Mendeleev - 157 and 81 g/mol, respectively. m(C 6 H 5 Br) = 0.5×157 = 78.5 g; m(HBr) = 0.5 x 81 = 40.5 g.
Answer	The reaction products are bromobenzene and hydrogen bromide. The masses of bromobenzene and hydrogen bromide are 78.5 and 40.5 g, respectively.

Physical properties

Benzene and its closest homologues are colorless liquids with a specific odor. Aromatic hydrocarbons are lighter than water and do not dissolve in it, but they easily dissolve in organic solvents - alcohol, ether, acetone.

Benzene and its homologues are themselves good solvents for many organic substances. All arenas burn with a smoky flame due to the high carbon content of their molecules.

The physical properties of some arenes are presented in the table.

Table. Physical properties of some arenas

Name	Formula	t°.pl., °C	t°.bp., °C
Benzene	C 6 H 6	5,5	80,1
Toluene (methylbenzene)	C 6 H 5 CH 3	95,0	110,6
Ethylbenzene	C 6 H 5 C 2 H 5	95,0	136,2
Xylene (dimethylbenzene)	C 6 H 4 (CH 3) 2
ortho-		25,18	144,41
meta-		47,87	139,10
pair-		13,26	138,35
Propylbenzene	C 6 H 5 (CH 2) 2 CH 3	99,0	159,20
Cumene (isopropylbenzene)	C 6 H 5 CH(CH 3) 2	96,0	152,39
Styrene (vinylbenzene)	C 6 H 5 CH \u003d CH 2	30,6	145,2

Benzene - low-boiling ( tkip= 80.1°C), colorless liquid, insoluble in water

Attention! Benzene - poison, acts on the kidneys, changes the blood formula (with prolonged exposure), can disrupt the structure of chromosomes.

Most aromatic hydrocarbons are life threatening and toxic.

Obtaining arenes (benzene and its homologues)

In the laboratory

1. Fusion of salts of benzoic acid with solid alkalis

C 6 H 5 -COONa + NaOH t → C 6 H 6 + Na 2 CO 3

sodium benzoate

2. Wurtz-Fitting reaction: (here G is halogen)

From 6H 5 -G+2Na + R-G →C 6 H 5 - R + 2 NaG

WITH 6 H 5 -Cl + 2Na + CH 3 -Cl → C 6 H 5 -CH 3 + 2NaCl

In industry

• isolated from oil and coal by fractional distillation, reforming;
• from coal tar and coke oven gas

1. Dehydrocyclization of alkanes with more than 6 carbon atoms:

C 6 H 14 t , kat→C 6 H 6 + 4H 2

2. Trimerization of acetylene(only for benzene) – R. Zelinsky:

3C 2 H2 600°C, Act. coal→C 6 H 6

3. Dehydrogenation cyclohexane and its homologues:

Soviet Academician Nikolai Dmitrievich Zelinsky established that benzene is formed from cyclohexane (dehydrogenation of cycloalkanes

C 6 H 12 t, cat→C 6 H 6 + 3H 2

C 6 H 11 -CH 3 t , kat→C 6 H 5 -CH 3 + 3H 2

methylcyclohexanetoluene

4. Alkylation of benzene(obtaining homologues of benzene) – r Friedel-Crafts.

C 6 H 6 + C 2 H 5 -Cl t, AlCl3→C 6 H 5 -C 2 H 5 + HCl

chloroethane ethylbenzene

Chemical properties of arenes

I. OXIDATION REACTIONS

1. Combustion (smoky flame):

2C 6 H 6 + 15O 2 t→12CO 2 + 6H 2 O + Q

2. Benzene under normal conditions does not decolorize bromine water and an aqueous solution of potassium permanganate

3. Benzene homologues are oxidized by potassium permanganate (discolor potassium permanganate):

A) in an acidic environment to benzoic acid

Under the action of potassium permanganate and other strong oxidants on the homologues of benzene, the side chains are oxidized. No matter how complex the chain of the substituent is, it is destroyed, with the exception of the a -carbon atom, which is oxidized into a carboxyl group.

Homologues of benzene with one side chain give benzoic acid:

Homologues containing two side chains give dibasic acids:

5C 6 H 5 -C 2 H 5 + 12KMnO 4 + 18H 2 SO 4 → 5C 6 H 5 COOH + 5CO 2 + 6K 2 SO 4 + 12MnSO 4 + 28H 2 O

5C 6 H 5 -CH 3 + 6KMnO 4 + 9H 2 SO 4 → 5C 6 H 5 COOH + 3K 2 SO 4 + 6MnSO 4 + 14H 2 O

Simplified :

C 6 H 5 -CH 3 + 3O KMnO4→C 6 H 5 COOH + H 2 O

B) in neutral and slightly alkaline to salts of benzoic acid

C 6 H 5 -CH 3 + 2KMnO 4 → C 6 H 5 COO K + K OH + 2MnO 2 + H 2 O

II. ADDITION REACTIONS (harder than alkenes)

1. Halogenation

C 6 H 6 + 3Cl 2 h ν → C 6 H 6 Cl 6 (hexachlorocyclohexane - hexachloran)

2. Hydrogenation

C 6 H 6 + 3H 2 t , PtorNi→C 6 H 12 (cyclohexane)

3. Polymerization

III. SUBSTITUTION REACTIONS – ionic mechanism (lighter than alkanes)

1. Halogenation -

a ) benzene

C 6 H 6 + Cl 2 AlCl 3 → C 6 H 5 -Cl + HCl (chlorobenzene)

C 6 H 6 + 6Cl 2 t ,AlCl3→C 6 Cl 6 + 6HCl( hexachlorobenzene)

C 6 H 6 + Br 2 t,FeCl3→ C 6 H 5 -Br + HBr( bromobenzene)

b) benzene homologues upon irradiation or heating

In terms of chemical properties, alkyl radicals are similar to alkanes. Hydrogen atoms in them are replaced by halogens by a free radical mechanism. Therefore, in the absence of a catalyst, heating or UV irradiation leads to a radical substitution reaction in the side chain. The influence of the benzene ring on alkyl substituents leads to the fact that the hydrogen atom is always replaced at the carbon atom directly bonded to the benzene ring (a-carbon atom).

1) C 6 H 5 -CH 3 + Cl 2 h ν → C 6 H 5 -CH 2 -Cl + HCl

c) benzene homologues in the presence of a catalyst

C 6 H 5 -CH 3 + Cl 2 AlCl 3 → (mixture of orta, pair of derivatives) +HCl

2. Nitration (with nitric acid)

C 6 H 6 + HO-NO 2 t, H2SO4→C 6 H 5 -NO 2 + H 2 O

nitrobenzene - smell almond!

C 6 H 5 -CH 3 + 3HO-NO 2 t, H2SO4→ WITH H 3 -C 6 H 2 (NO 2) 3 + 3H 2 O

2,4,6-trinitrotoluene (tol, trotyl)

The use of benzene and its homologues

Benzene C 6 H 6 is a good solvent. Benzene as an additive improves the quality of motor fuel. It serves as a raw material for the production of many aromatic organic compounds - nitrobenzene C 6 H 5 NO 2 (solvent, aniline is obtained from it), chlorobenzene C 6 H 5 Cl, phenol C 6 H 5 OH, styrene, etc.

Toluene C 6 H 5 -CH 3 - a solvent used in the manufacture of dyes, drugs and explosives (trotyl (tol), or 2,4,6-trinitrotoluene TNT).

Xylene C 6 H 4 (CH 3) 2 . Technical xylene is a mixture of three isomers ( ortho-, meta- and pair-xylenes) - is used as a solvent and starting product for the synthesis of many organic compounds.

Isopropylbenzene C 6 H 5 -CH (CH 3) 2 serves to obtain phenol and acetone.

Chlorine derivatives of benzene used for plant protection. Thus, the product of substitution of H atoms in benzene with chlorine atoms is hexachlorobenzene C 6 Cl 6 - a fungicide; it is used for dry seed dressing of wheat and rye against hard smut. The product of the addition of chlorine to benzene is hexachlorocyclohexane (hexachloran) C 6 H 6 Cl 6 - an insecticide; it is used to control harmful insects. These substances refer to pesticides - chemical means of combating microorganisms, plants and animals.

Styrene C 6 H 5 - CH \u003d CH 2 polymerizes very easily, forming polystyrene, and copolymerizing with butadiene - styrene-butadiene rubbers.

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