Home / Self-development/ Benzene can be converted to cyclohexane by hydrogenation. Cycloalkanes

Benzene can be converted to cyclohexane by hydrogenation. Cycloalkanes

Cycloalkanes (cycloparaffins, naphthenes) are cyclic saturated hydrocarbons, according to chemical structure close to alkanes. They contain only simple single sigma bonds (σ bonds), and do not contain aromatic bonds.

Cycloalkanes have a higher density and higher melting and boiling points than the corresponding alkanes. The general formula of their homologous series is C n H 2n.

Nomenclature and isomerism of cycloalkanes

The names of cycloalkanes are formed by adding the prefix "cyclo-" to the name of the alkane with the corresponding number: cyclopropane, cyclobutane, etc.

Like alkanes, the carbon atoms of cycloalkanes are sp 3 hybridized.

In addition to isomerism of the carbon skeleton, cycloalkanes are characterized by interclass isomerism with alkenes and spatial geometric isomerism in the form of the existence of cis- and trans-isomers.

Preparation of cycloalkanes

In industry, cycloalkanes are obtained in several ways:

IN laboratory conditions Cycloalkanes can be prepared by the dehalogenation reaction of dihaloalkanes.

Chemical properties cycloalkanes

It is important to note that cyclopropane and cyclobutane enter into addition reactions, exhibiting the properties of unsaturated compounds. For cyclopentane and cyclohexane, addition reactions are not typical; they predominantly undergo substitution reactions.

This article was written by Yuri Sergeevich Bellevich and is his intellectual property. Copying, distribution (including by copying to other sites and resources on the Internet) or any other use of information and objects without the prior consent of the copyright holder is punishable by law. To obtain article materials and permission to use them, please contact

Cycloalkanes – these are saturated (saturated) hydrocarbons that contain a closed carbon cycle.

General formula of cycloalkanes CnH2n, Where n≥3.

Structure of cycloalkanes

The carbon atoms in cycloalkane molecules are in a state of sp 3 hybridization and form four σ bonds C–C and C–H. Bond angles change depending on the size of the cycle.

The simplest cycloalkane, cyclopropane, is essentially a flat triangle.

σ-Bonds in cyclopropane are called "banana". They do not lie along the axis connecting the atomic nuclei, but deviate from it, reducing the tension in the cyclopropane molecule.

The properties of “banana” bonds resemble π bonds. They tear easily.

Therefore, cyclopropane very easily enters into addition reactions with rupture of the carbon ring.

The remaining cycloalkanes have a nonplanar structure. The cyclobutane molecule has an inflection along the line connecting the first and third carbon atoms in the ring:

Cyclobutane also reacts accessions, but the angular stress in cyclobutane is less than in cyclopropane, so addition reactions to cyclobutane are more difficult.

Large rings have a more complex, non-planar structure, as a result of which the angular stress in the molecules of large cycloalkanes is almost absent.

Cycloalkanes with a large ring do not undergo addition reactions. They are characterized by substitution reactions.

The structure of cyclopentane is also non-planar; the molecule is a so-called “envelope”.

The cyclohexane molecule is not a flat polygon and takes on different conformations called “chair” and “bathtub”:

"armchair" "bath"

Isomerism of cycloalkanes

Structural isomerism

Cycloalkanes are characterized by structural isomerism, associated with the different number of carbon atoms in the ring, the different number of carbon atoms in the substituents and the position of the substituents in the ring.

Isomers with different numbers of carbon atoms in the ring differ in the size of the carbon cycle.

Ethylcyclopropane	Methylcyclobutane

Isomers with different numbers of carbon atoms in substituents differ in the structure of substituents on the same carbon cycle.

1-Methyl-2-propylcyclopentane	1,2-Diethylcyclopentane

Isomers with different positions identical substituents in the carbon cycle.

For example.

1,1-Dimethylcyclohexane	1,2-Dimethylcyclohexane

Interclass isomerism: Cycloalkanes are isomers of alkenes.

Cyclopropane	Propylene

Geometric (cis-trans) isomerism

For cycloalkanes with two substituents located at adjacent carbon atoms in the ring, cis-trans isomerism is due to various relative position in the space of substituents relative to the plane of the cycle.

cis-1,2-Dimethylcyclopropane	trance-1,2-Dimethylcyclopropane

For 1,1-dimethylcyclopropane cis-trans-isomerism is not typical.

Nomenclature of cycloalkanes

The names of cycloalkanes use the prefix -CYCLO.

Name of cycloalkane	Structural formula
Cyclopropane
Cyclobutane
Cyclopentane
Cyclohexane

The naming of cycloalkanes is based on the following rules:

1. The cycle is taken to be Gmain carbon chain. At the same time, it is believed that hydrocarbon radicals, which are not included in the main chain, are in it deputies.

2. Number the carbon atoms in the ring so that the carbon atoms that are connected to substituents receive minimum possible numbers. Moreover, the numbering should begin with closer to senior group end of the chain.

3. All radicals are named, indicating in front the numbers that indicate their location in the main chain.

For identical substituents, these numbers are indicated separated by commas, while the number of identical substituents is indicated by prefixes di-(two), three-(three), tetra-(four), penta-(five), etc.

For example, 1,1-dimethylcyclopropane or 1,1,3-trimethylcyclopentane.

4. The names of the deputies with all prefixes and numbers are arranged in alphabetical order.

For example: 1,1-dimethyl-3-ethylcyclopentane.

5. It's called the carbon cycle.

Chemical properties of cycloalkanes

Small ring cycloalkanes (cyclopropane, cyclobutane and their substituted homologues) due to the high tension in the ring, they can react accession.

1. Addition reactions to cycloalkanes

1.1. Hydrogenation of cycloalkanes

Small cycles, as well as (under harsh conditions) cyclopentane, can react with hydrogen. This causes ring rupture and the formation of an alkane.

Cyclopropane and cyclobutane Hydrogen is added quite easily when heated in the presence of a catalyst:

Cyclopentane adds hydrogen under harsh conditions:

Bromination occurs more slowly and selectively.

Cyclohexane and cycloalkanes with large number carbon atoms in the cycle do not react with hydrogen.

1.2. Halogenation of cycloalkanes

Cyclopropane and cyclobutane react with halogens, and halogens also join the molecule, accompanied by ring rupture.

1.3. Hydrohalogenation

Cyclopropane and its homologues with alkyl substituents on the three-membered ringenter into ring-breaking addition reactions with hydrogen halides.

2. Substitution reactions

2.1. Halogenation

Halogenation of cyclopentane, cyclohexane and cycloalkanes with a large number of carbon atoms in the cycle proceeds according to the mechanism radical substitution.

When methylcyclopentane is chlorinated, substitution occurs predominantly at the tertiary carbon atom:

2.2. Nitration of cycloalkanes

When cycloalkanes interact with dilute nitric acid When heated, nitrocycloalkanes are formed.

2.3. Dehydrogenation

When cycloalkanes are heated in the presence of catalysts, dehydrogenation – elimination of hydrogen.

Cyclohexane and its derivatives are dehydrogenated by heating and under the action of a catalyst to benzene and its derivatives.

3. Oxidation of cycloalkanes

3.1. Combustion

Like all hydrocarbons, alkanes burn to carbon dioxide and water. The combustion equation for cycloalkanes in general form:

C n H 2n + 3n/2O 2 → nCO 2 + nH 2 O + Q

2C 5 H 10 + 15O 2 → 10CO 2 + 10H 2 O + Q

Laboratory lesson

"Chemical properties of arenes".

Goals : highlight the main chemical properties of arenes;

Tasks : give the concept of defining arenes, determine what kind of reactions arenes can enter into, highlight the main chemical properties of arenes:

Lead time: 1 hour

The order of work.

Write down the topic of the laboratory lesson;

Write down the goals and objectives of the lesson;

Complete the practical part of the lesson;

Answer questions to reinforce the material studied in the laboratory lesson;

Theoretical part.

Arene substitution reactions.

The arene core has a mobileπ - a system that is affected by electrophilic reagents. Arenes are characterized by electrophilic substitution, which can be represented as follows:

An electrophilic particle is attracted toπ -ring system, then a strong bond is formed between the reagentXand one of the carbon atoms, in which case the unity of the ring is disrupted. To restore aromaticity, a proton is emitted and 2 electronsS-Npass into the π-system of the ring.

1. Halogenation occurs in the presence of catalysts - anhydrous and bromides:

2. Nitration of arenes. Benzene reacts very slowly with concentrated with strong heating. But if you add , then the reaction proceeds very easily:

3. Sulfonation occurs under the influence of 100% sulfuric acid – oleum:

4. Alkylation . As a result, chain elongation occurs, the reaction proceeds in the presence of a catalyst - aluminum chloride:

Arene addition reactions.

1. Hydrogenation (with catalysts) of arenes:

2. Radical halogenation due to the interaction of benzene vapor and strong UV radiation. As a result, a solid product is formed -WITH 6 H 6 Cl 6 :

3. air. The reaction occurs at vanadium (V) oxide and 400°C:

Benzene homologues have a number of differences - for their products I am the initial substituent in the ring:

Substitution in the ring is possible only in the presence of a catalyst (iron and aluminum chloride); the substitution occurs in the ortho- and para-positions relative to the alkyl radical:

If strong oxidizing agents act ( ), then the alkyl chain is destroyed and benzoic acid is formed:

Practical part.

Organic substance, the molecular formula of which is C7H8, belongs to the homologous series

1) methane 2) ethylene 3) benzene 4) acetylene

Toluene is a member of the homologous series

1) phenol 2) benzene 3) methanol 4) styrene

A homologue of benzene is a substance whose formula is

1) C8H18 2) C8H10 3) C8H16 4) C8H14

An isomer of benzene is a compound whose formula is

1) C6H5−CH=CH−CH3 2) CH3−CH−C≡C−CH−CH3

3) CH2=CH−CH2−CH2−CH2−CH3 4) CH2=CH−C≡C−CH=CH2

Toluene and ethylbenzene are

1) homologues 2) structural isomers

3) geometric isomers 4) the same substance

A representative of the homologous series of benzene is

1) toluene 2) phenol 3) styrene 4) methanol

A compound in which all carbon atoms are in a state of sp2 hybridization is

1) ethylbenzene 2) benzene 3) methylcyclohexane 4) butene-1

In a chain of transformations

the final product "X3" has the formula

2) 3) 4)

Write the reaction equations that can be used to carry out the following transformations:

Benzene can be converted to cyclohexane by the reaction

1) hydrogenation 2) hydration 3) dehydrogenation 4) dehydration

Benzene is formed as a result of trimerization

1) ethene 2) ethane 3) ethanol 4) ethyne

Benzene can be obtained from acetylene in one step by the reaction

1) dehydrogenation 2) trimerization 3) hydrogenation 4) hydration

1) does not burn in air 2) reacts with KMnO4 solution

3) enters into hydrogenation reactions 4) reacts with bromine in the presence of a catalyst

Benzene is able to interact with each of two substances:

1) H2 and HBr 2) HNO3 and KMnO4 3) C2H5Cl and HNO3 4) CH3OH and C2H6

Benzene undergoes a substitution reaction with

1) bromine and nitric acid 2) oxygen and sulfuric acid

3) chlorine and hydrogen 4) nitric acid and hydrogen

Benzene reacts with each of two substances:

1) C2H5OH and N2 2) HNO3 and HBr 3) H2O and O2 4) CH3Cl and Br2

In the transformation scheme C6H14 → X → C6H5CH3, substance “X” is

1) C6H5OH 2) C6H10 3) C6H13COOH 4) C6H6

To obtain cyclohexane from benzene, use the reaction

1) dehydrogenation 2) halogenation 3) hydrogenation 4) hydration

Chlorobenzene is formed when benzene reacts with

1) chlorine (UV) 2) chlorine (FeCl3) 3) hydrogen chloride 4) chloromethane

Benzene does not interact with

1) nitric acid 2) bromine 3) hydrogen bromide 4) oxygen

Each of two substances interacts with toluene:

1) CH3OH and Ag2O 2) KMnO4 and H2 3) Cl2 and NaOH 4) HNO3 and CH3OCH3

In the transformation scheme C6H6→X1→X2→+ Cl- substances “X1” and “X2” are respectively:

1) C6H5NO2AndC6H5Cl 2) C6H5OHAndC6H5Cl

3) C6H5OHAndC6H5NO2 4) C6H5NO2AndC6H5NH2

Hexachlorocyclohexane is formed as a result of the interaction

1) chlorine and benzene 2) chlorine and cyclohexane

3) hydrogen chloride and benzene 4) chlorine and hexane

Toluene, unlike benzene,

1) undergoes hydrogenation 2) is oxidized by atmospheric oxygen

3) reacts with chlorine (in the presence of AlCl3) 4) is oxidized with a solution of potassium permanganate

The similarity of the chemical properties of benzene and saturated hydrocarbons is manifested in the reaction

1) C6H6 + 3H2 → C6H12 2) C6H6 + C2H4 → C6H5 – C2H5

3) C6H6 + 3Cl2 → C6H6Cl6 4) C6H6 + Br2 → C6H5Br + HBr

When hydrogen reacts with benzene, it forms

1) toluene 2) hexanol-1 3) acetylene 4) cyclohexane

Are the following judgments about properties true? aromatic hydrocarbons?

A. Benzene decolorizes a solution of potassium permanganate.

B. Toluene undergoes a polymerization reaction.

1) only A is true 2) only B is true 3) both judgments are correct 4) both judgments are incorrect

In the scheme methane → X → benzene, compound “X” is

1) chloromethane 2) ethylene 3) hexane 4) ethylene

Toluene can be formed during aromatization (dehydrocyclization)

Benzene can be produced by trimerization reaction

1) cyclohexane 2) ethane 3) ethylene 4) acetylene

Both ethylene and benzene are characterized by:

1) hydrogenation reaction 2) the presence of only π-bonds in molecules

3) sp2 hybridization of carbon atoms in molecules 4) high solubility in water

5) interaction with ammonia solution silver (I) oxide 6) combustion in air

Toluene reacts with

1) hydrogen 2) water 3) zinc

4) nitric acid 5) hydrogen chloride 6) chlorine

Both acetylene and toluene are characterized by:

1) polymerization reaction 2) sp2 hybridization of carbon atoms in the molecule

3) oxidation with potassium permanganate 4) halogenation reaction

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 are easily soluble in organic solvents - alcohol, ether, acetone.

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

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

Table. Physical properties of some arenas

Name	Formula	t°.pl., °C	t°.b.p., °C
Benzene	C6H6	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=CH 2	30,6	145,2

Benzene – low boiling ( tbale= 80.1°C), colorless liquid, insoluble in water

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

Most aromatic hydrocarbons are life-threatening and toxic.

Preparation of arenes (benzene and its homologues)

In the laboratory

1. Fusion of benzoic acid salts with solid alkalis

C6H5-COONa + NaOH t → C 6 H 6 + Na 2 CO 3

sodium benzoate

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

C 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 and reforming;
from coal tar and coke oven gas

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

C6H14 t , kat→C 6 H 6 + 4H 2

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

3С 2 H 2 600°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

C6H12 t, kat→C 6 H 6 + 3H 2

C6H11-CH3 t , kat→C 6 H 5 -CH 3 + 3H 2

methylcyclohexantoluene

4. Alkylation of benzene(preparation of benzene homologues) – 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 (smoking flame):

2C6H6 + 15O2 t→12CO 2 + 6H 2 O + Q

2. Under normal conditions, benzene does not discolor bromine water and aqueous solution potassium permanganate

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

A) in an acidic environment to benzoic acid

When benzene homologues are exposed to potassium permanganate and other strong oxidizing agents, 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 :

C6H5-CH3+3O KMnO4→C 6 H 5 COOH + H 2 O

B) in neutral and slightly alkaline to benzoic acid salts

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 → C6H6Cl6 (hexachlorocyclohexane - hexachlorane)

2. Hydrogenation

C6H6 + 3H2 t , PtorNi→C 6 H 12 (cyclohexane)

3. Polymerization

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

b) benzene homologues upon irradiation or heating

The chemical properties of alkyl radicals are similar to alkanes. The hydrogen atoms in them are replaced by halogen by a free radical mechanism. Therefore, in the absence of a catalyst, upon heating or UV irradiation, a radical substitution reaction occurs in the side chain. The influence of the benzene ring on alkyl substituents leads to the fact that the hydrogen atom is always replaced by the carbon atom directly bonded to 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 orth, 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 almonds!

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, TNT)

Application 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 from which aniline is obtained), chlorobenzene C 6 H 5 Cl, phenol C 6 H 5 OH, styrene, etc.

Toluene C 6 H 5 –CH 3 – solvent, used in the production of dyes, medicinal and explosives (TNT (TNT), or 2,4,6-trinitrotoluene TNT).

Xylenes C6H4(CH3)2. Technical xylene is a mixture of three isomers ( ortho-, meta- And pair-xylenes) – used as a solvent and starting product for the synthesis of many organic compounds.

Isopropylbenzene C 6 H 5 –CH(CH 3) 2 is used to produce phenol and acetone.

Chlorinated derivatives of benzene used for plant protection. Thus, the product of the replacement of H atoms in benzene with chlorine atoms is hexachlorobenzene C 6 Cl 6 - a fungicide; it is used for dry treatment of wheat and rye seeds against smut. The product of the addition of chlorine to benzene is hexachlorocyclohexane (hexachlorane) C 6 H 6 Cl 6 - an insecticide; it is used to control harmful insects. The substances mentioned belong to pesticides - chemical means of combating microorganisms, plants and animals.

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

VIDEO EXPERIENCES