We present to your attention a video lesson on the topic "Chemical properties of benzene". Using this video, you can get an idea of the chemical properties of benzene, as well as the harsh conditions that are required for benzene to react with other substances.
Topic:aromatic hydrocarbons
Lesson:Chemical properties of benzene
Rice. 1. Benzene molecule
Breaking the p-electron cloud in the benzene molecule is difficult. Therefore, benzene enters into chemical reactions much less actively than unsaturated compounds.
In order for benzene to enter into chemical reactions, rather harsh conditions are necessary: an elevated temperature, and in many cases a catalyst. In most reactions, the stable benzene ring is retained.
1. Bromination.
A catalyst (iron(III) or aluminum bromide) is required and even small amounts of water must not be allowed to enter. The role of the catalyst is that the bromine molecule is attracted by one of the bromine atoms to the iron atom. As a result, it polarizes - a pair of bond electrons passes to the bromine atom associated with iron:
Br+…. Br - FeBr 3 .
Br+ is a strong electrophile. It is attracted to the six-electron cloud of the benzene ring and breaks it, forming a covalent bond with the carbon atom:
The bromine anion could join the resulting cation. But the reduction of the aromatic system of the benzene ring is energetically more favorable than the addition of the bromine anion. Therefore, the molecule goes into a stable state by throwing out a hydrogen ion:
All electrophilic substitution reactions in the benzene ring proceed according to a similar mechanism.
2. Nitration
Benzene and its homologues react with a mixture of concentrated sulfuric and nitric acids (nitrating mixture). In the nitrating mixture, in equilibrium, there is a nitronium ion NO 2 +, which is an electrophile:
3. Sulfonation.
Benzene and other arenes, when heated, react with concentrated sulfuric acid or oleum - a solution of SO 3 in sulfuric acid:
4 . Friedel-Crafts Alkylation
5. Alkylation with alkenes
These reactions are energetically unfavorable, therefore, they proceed only when heated or irradiated.
1. Hydrogenation.
When heated, at elevated pressure, and in the presence of a Ni, Pt, or Pd catalyst, benzene and other arenes add hydrogen to form cyclohexane:
2. Chlorination of benzene.
Under the action of ultraviolet radiation, benzene adds chlorine. If a quartz glass flask with a solution of chlorine in benzene is exposed to sunlight, the solution will quickly discolor, chlorine will combine with benzene to form 1,2,3,4,5,6-hexachlorocyclohexane, which is known as hexachlorane(previously used as an insecticide):
3. burning benzene.
Unlike alkanes, the flame of benzene and other aromatic hydrocarbons is bright and smoky.
Summing up the lesson
In this lesson, you studied the topic "Chemical Properties of Benzene". By using this material, you were able to get an idea of the chemical properties of benzene, as well as the harsh conditions that are required for benzene to react with other substances.
Bibliography
1. Rudzitis G.E. Chemistry. Fundamentals of General Chemistry. Grade 10: textbook for educational institutions: basic level / G. E. Rudzitis, F.G. Feldman. - 14th edition. - M.: Education, 2012.
2. Chemistry. Grade 10. Profile level: textbook. for general education institutions / V.V. Eremin, N.E. Kuzmenko, V.V. Lunin and others - M.: Drofa, 2008. - 463 p.
3. Chemistry. Grade 11. Profile level: textbook. for general education institutions / V.V. Eremin, N.E. Kuzmenko, V.V. Lunin and others - M.: Drofa, 2010. - 462 p.
4. Khomchenko G.P., Khomchenko I.G. Collection of problems in chemistry for those entering the universities. - 4th ed. - M.: RIA "New Wave": Publisher Umerenkov, 2012. - 278 p.
Homework
1. No. 13, 14 (p. 62) Rudzitis G.E., Feldman F.G. Chemistry: Organic Chemistry. Grade 10: textbook for educational institutions: basic level / G. E. Rudzitis, F.G. Feldman. - 14th edition. - M.: Education, 2012.
2. Why do aromatic compounds differ in chemical properties from both saturated and unsaturated hydrocarbons?
3. Write the equations for the combustion reactions of ethylbenzene and xylene.
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).
Later electron diffraction studies 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).
PRTSVSH (F) FGBOU VPO
Department of "Fire Safety"
Test
in the discipline "Theory of combustion and explosions"
Task number 1
Determine the specific theoretical quantities and volume of air required for the complete combustion of benzene vapor. The conditions in which the air is located are characterized by temperature Tv and pressure Pv, and benzene vapor - temperature Tg and pressure Pg. Express the calculation results in the following units: ; ;;;
Initial data (N - group number, n - number according to the list of students:
TV=300+(-1) N *2*N-(-1) n *0.2*n= 277.6 K
Pv \u003d? 10 3 \u003d 95900 Pa;
Тg=300?(?1) N?2?N?(?1) n?0.2?n= 321.6 K;
Pr \u003d? 10 3 \u003d 79400 Pa.
С6Н6+7.5О2+7.5?3.76N2=6CO2+3pO+7.5?3.76N2+Qp (1),
where Qp is the heat of a chemical reaction. From this equation, it is possible to determine the stoichiometric coefficients of benzene and molecular oxygen: Vg = 1, V0 = 7.5
2. Specific theoretical amount of air - the number of kilomoles of air that are necessary for the complete combustion of one kilomol of benzene is calculated by the formula:
where 4.76 is the amount of air that contains a unit of oxygen, \u003d is the ratio of the stoichiometric coefficients of molecular oxygen (Vo) and benzene (Vg)
Substituting in (d) the values of Vo and Vg, we obtain:
3. The volume of air required for the complete combustion of one kilomole of benzene is determined as follows:
where is the volume of one kilomole of air at temperature Tv and pressure Pv. The value is calculated using the formula
where 22.4 is the molar volume of gas under normal conditions, Po = 101325 Pa is normal pressure, To = 273 K is normal temperature.
Substituting Tv, To, Pv, Po in (5), we obtain
The specific theoretical air volume is calculated by the formula (4):
4. The volume of air required for the complete combustion of a unit volume of gaseous fuel is determined as follows:
where is the volume of one kilomole of fuel - benzene vapor at temperature Tg and pressure Pg. Given that
and substituting (8) and (5) into (7), we obtain the following expression for the specific theoretical air volume:
We calculate the value of this parameter of the combustion process:
The volume of air required for the complete combustion of one kilogram of benzene is determined as follows:
where - the molar mass of fuel is the mass of one kilomole of benzene, expressed in kilograms. The molar mass of benzene is numerically equal to its molecular weight is found by the formula:
Ac?nc + An?nn, UiAi?ni (11)
where Ac and An are the atomic weights of carbon and hydrogen, nc and nn are the numbers of carbon atoms in the benzene molecule. Substituting the values Ac = 12, nc = 6, An = 1, nn = 6, we get:
We find the specific theoretical volume of air by substituting the values of n into and into formula (10):
Calculation result:
Task number 2
Determine the specific theoretical quantity, volume and composition of benzene combustion products, if the coefficient of excess air c, temperature Tp and pressure Pp of combustion products, temperature Tg and pressure Pg of benzene vapor are known. Express the calculation results in mole fractions (in percent) and in the following units: ; ;;
Initial data:
c=1.5+(?1) N?0.1?N?(?1) n?0.01?n = 0.2;
Rp \u003d? 10 3 \u003d 68400 Pa;
Tp=1600?(?1) N?20?N?(?1) n?2?n = 1816 K;
Тg=273?(?1) N?2?N+(?1) n?0.2?n = 295.4 K;
Rg \u003d? 10 3 \u003d 111600 Pa;
solution (N=11, n=2).
1. We write the stoichiometric equation for the reaction of benzene combustion in air:
C 6 H 6 +7.5O 2 +7.5? 3.76N 2 \u003d 6CO 2 + 3H 2 O + 7.5? 3.76N 2 + Qp, (1)
where Qp is the heat of a chemical reaction. From this equation, we determine the following stoichiometric coefficients:
V CO2 \u003d 6, V pO \u003d 3, V C6H6 \u003d 1, V O2 \u003d 7.5, V N2 \u003d 7.5? 3.76
2. Determine the estimated amount of combustion products of one kilomole of fuel:
Substituting in (2) the values of the stoichiometric coefficients of combustion products and fuel, we obtain:
3. Specific theoretical amount of air - the number of kilomoles of air necessary for the complete combustion of one kilomol of fuel, we determine using the formula:
Where 4.76 is the amount of air that contains a unit of oxygen,
Ratio of stoichiometric coefficients of molecular oxygen and benzene.
Substituting in (4) the values V O2 =7.5 and V C6H6 =1 , we obtain:
4. The excess amount of air that falls on 1 Kmol of fuel is determined by the expression:
benzene steam combustion air
Substituting in this expression the values
37,7(0,2-1)=30,16(7)
5. The total amount of combustion products per unit amount of fuel substance is determined by the sum:
After substituting the values and we get:
6. Mole fractions of combustion products, expressed as a percentage, are determined as follows:
In formulas (9) for the mole fractions of nitrogen and oxygen in the combustion products, 0.79 and 0.21 are the mole fractions of these substances in the air, the excess of which leads to an increase in the proportion of nitrogen and the appearance of oxygen in the combustion products.
7. To determine the specific volumes and products of combustion, it is necessary to calculate their molar volume - the volume of one kilomole of gas under the conditions in which the products are located:
where 22.4 is the volume of one kilomole of gas under normal conditions, T 0 \u003d 273K - normal temperature, Po \u003d 101325 Pa - normal pressure.
Substituting in (10) the values, Po, To, we get:
The volume of products that are formed during the combustion of one kilogram of fuel, excluding excess air, is calculated as follows:
where - the molar mass of fuel is the mass of one kilomole of benzene, expressed in kilograms. The molar mass of benzene is found by the formula:
where Ac and An are the atomic weights of carbon (12) and hydrogen (1), n c and n n are the numbers of carbon (6) and hydrogen (6) atoms in benzene molecules (C 6 H 6).
Substituting the values, and in (12) we obtain
The excess volume of air per 1 kilogram of fuel is determined as follows:
where is the volume of one kilomole of excess air, which is part of the combustion products. Since the temperature and pressure of excess air correspond to the temperature and pressure of the combustion products, then \u003d \u003d 220.7.
Substituting this value, as well as in (14), we obtain:
To calculate the specific volume of products of complete combustion of fuel, we assume that benzene vapor has a temperature Tg at pressure:
where is the volume of one kilomole of benzene vapor at temperature Tg and pressure Pg. The molar volume of fuel is calculated by the formula:
Substituting the obtained value, and such values in (17), we obtain:
The excess volume of air per cubic meter of benzene vapor is determined as follows:
Substitution in (20) values \u003d 30.16 , \u003d and
gives the following result:
The total specific volume of combustion products, taking into account excess air, is determined by the sum
Calculation result:
X CO2 \u003d%; X H2O \u003d 4.4%; X N2 =%; X O2 \u003d 11.7%
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The first group of reactions is substitution reactions. We said that arenes do not have multiple bonds in the molecular structure, but contain a conjugated system of six electrons, which is very stable and gives additional strength to the benzene ring. Therefore, in chemical reactions, first of all, the substitution of hydrogen atoms occurs, and not the destruction of the benzene ring.
We have already encountered substitution reactions when talking about alkanes, but for them these reactions proceeded according to a radical mechanism, and for arenes the ionic mechanism of substitution reactions is characteristic.
First chemical property halogenation. Substitution of a hydrogen atom for a halogen atom chlorine or bromine.
The reaction proceeds when heated and always with the participation of a catalyst. In the case of chlorine, it can be aluminum chloride or iron chloride three. The catalyst polarizes the halogen molecule, resulting in heterolytic bond breaking and ions are obtained.
The positively charged chloride ion reacts with benzene.
If the reaction occurs with bromine, then iron tribromide or aluminum bromide acts as a catalyst.
It is important to note that the reaction occurs with molecular bromine and not with bromine water. Benzene does not react with bromine water.
The halogenation of benzene homologues has its own characteristics. In the toluene molecule, the methyl group facilitates substitution in the ring, the reactivity increases, and the reaction proceeds under milder conditions, that is, already at room temperature.
It is important to note that the substitution always occurs in the ortho and para positions, so a mixture of isomers is obtained.
Second property nitration of benzene, introduction of a nitro group into the benzene ring.
A heavy yellowish liquid with the smell of bitter almonds nitrobenzene is formed, so the reaction can be qualitative for benzene. For nitration, a nitrating mixture of concentrated nitric and sulfuric acids is used. The reaction is carried out by heating.
Let me remind you that for the nitration of alkanes in the Konovalov reaction, dilute nitric acid was used without the addition of sulfuric acid.
In the nitration of toluene, as well as in the halogenation, a mixture of ortho- and para-isomers is formed.
Third property alkylation of benzene with haloalkanes.
This reaction allows the introduction of a hydrocarbon radical into the benzene ring and can be considered a method for obtaining benzene homologues. Aluminum chloride is used as a catalyst, which promotes the decomposition of the haloalkane molecule into ions. It also needs heating.
Fourth property alkylation of benzene with alkenes.
In this way, for example, cumene or ethylbenzene can be obtained. Catalyst aluminum chloride.
2. Reactions of addition to benzene
The second group of reactions is addition reactions. We said that these reactions are not characteristic, but they are possible under rather harsh conditions with the destruction of the pi-electron cloud and the formation of six sigma bonds.
Fifth property in the general list hydrogenation, addition of hydrogen.
Temperature, pressure, catalyst nickel or platinum. Toluene is able to react in the same way.
sixth property chlorination. Please note that we are talking specifically about the interaction with chlorine, since bromine does not enter into this reaction.
The reaction proceeds under hard ultraviolet irradiation. Hexachlorocyclohexane, another name for hexachlorane, is formed, a solid.
It is important to remember that for benzene not possible addition reactions of hydrogen halides (hydrohalogenation) and addition of water (hydration).
3. Substitution in the side chain of benzene homologues
The third group of reactions concerns only benzene homologues - this is a substitution in the side chain.
seventh property in the general list halogenation at the alpha carbon atom in the side chain.
The reaction occurs when heated or irradiated, and always only at the alpha carbon. As the halogenation continues, the second halogen atom will return to the alpha position.
4. Oxidation of benzene homologues
The fourth group of reactions is oxidation.
The benzene ring is too strong, so benzene does not oxidize potassium permanganate does not discolor its solution. This is very important to remember.
On the other hand, benzene homologues are oxidized with an acidified solution of potassium permanganate when heated. And this is the eighth chemical property.
It turns out benzoic acid. Discoloration of the solution is observed. In this case, no matter how long the carbon chain of the substituent is, it always breaks after the first carbon atom and the alpha atom is oxidized to a carboxyl group with the formation of benzoic acid. The rest of the molecule is oxidized to the corresponding acid or, if it is only one carbon atom, to carbon dioxide.
If the benzene homologue has more than one hydrocarbon substituent on the aromatic ring, then the oxidation occurs according to the same rules - the carbon in the alpha position is oxidized.
In this example, a dibasic aromatic acid is obtained, which is called phthalic acid.
In a special way, I note the oxidation of cumene, isopropylbenzene, with atmospheric oxygen in the presence of sulfuric acid.
This is the so-called cumene method for producing phenol. As a rule, one has to deal with this reaction in matters relating to the production of phenol. This is the industrial way.
ninth property combustion, complete oxidation with oxygen. Benzene and its homologues burn to carbon dioxide and water.
Let us write the equation for the combustion of benzene in a general form.
According to the law of conservation of mass, there should be as many atoms on the left as there are atoms on the right. Because, after all, in chemical reactions, atoms do not go anywhere, but the order of bonds between them simply changes. So there will be as many carbon dioxide molecules as there are carbon atoms in an arene molecule, since the molecule contains one carbon atom. That is n CO 2 molecules. There will be half as many water molecules as hydrogen atoms, that is, (2n-6) / 2, which means n-3.
There are the same number of oxygen atoms on the left and on the right. On the right, there are 2n from carbon dioxide, because there are two oxygen atoms in each molecule, plus n-3 from water, for a total of 3n-3. On the left, there are the same number of oxygen atoms 3n-3, which means that there are two times fewer molecules, because the molecule contains two atoms. That is (3n-3)/2 oxygen molecules.
Thus, we have compiled the equation for the combustion of benzene homologues in a general form.
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 about-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. |
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