Characteristic chemical properties of hydrocarbons: alkanes, alkenes, dienes, alkynes, aromatic hydrocarbons

Alkanes

Alkanes are hydrocarbons in whose molecules the atoms are linked by single bonds and which correspond to the general formula $C_(n)H_(2n+2)$.

Homologous series of methane

As you already know, homologues are substances that are similar in structure and properties and differ by one or more $CH_2$ groups.

Limit hydrocarbons make up the homologous series of methane.

Isomerism and nomenclature

Alkanes are characterized by the so-called structural isomerism. Structural isomers differ from each other in the structure of the carbon skeleton. As you already know, the simplest alkane, which is characterized by structural isomers, is butane:

Let us consider in more detail for alkanes the basics of the IUPAC nomenclature:

1. Choice of the main circuit.

The formation of the name of a hydrocarbon begins with the definition of the main chain - the longest chain of carbon atoms in the molecule, which is, as it were, its basis.

2.

The atoms of the main chain are assigned numbers. The numbering of atoms of the main chain starts from the end closest to the substituent (structures A, B). If the substituents are at an equal distance from the end of the chain, then the numbering starts from the end at which there are more of them (structure B). If different substituents are at an equal distance from the ends of the chain, then the numbering starts from the end to which the older one is closer (structure D). The seniority of hydrocarbon substituents is determined by the order in which the letter with which their name begins follows in the alphabet: methyl (—$CH_3$), then propyl ($—CH_2—CH_2—CH_3$), ethyl ($—CH_2—CH_3$ ) etc.

Note that the name of the substitute is formed by replacing the suffix -en to suffix -silt in the name of the corresponding alkane.

3. Name formation.

Numbers are indicated at the beginning of the name - the numbers of carbon atoms at which the substituents are located. If there are several substituents at a given atom, then the corresponding number in the name is repeated twice, separated by commas ($2.2-$). After the number, a hyphen indicates the number of substituents ( di- two, three- three, tetra- four, penta- five) and the name of the deputy ( methyl, ethyl, propyl). Then without spaces and hyphens - the name of the main chain. The main chain is called as a hydrocarbon - a member of the homologous series of methane ( methane, ethane, propane, etc.).

Names of substances structural formulas which are given above are as follows:

- structure A: $2$ -methylpropane;

- Structure B: $3$ -ethylhexane;

- Structure B: $2,2,4$ -trimethylpentane;

- structure Г: $2$ -methyl$4$-ethylhexane.

Physical and chemical properties of alkanes

physical properties. The first four representatives of the homologous series of methane are gases. The simplest of them is methane - a colorless, tasteless and odorless gas (the smell of gas, upon smelling which you need to call $104$, is determined by the smell of mercaptans - sulfur-containing compounds specially added to methane used in household and industrial gas appliances in order to make people those near them could smell the leak).

Hydrocarbons of composition from $С_5Н_(12)$ to $С_(15)Н_(32)$ are liquids; heavier hydrocarbons solids.

The boiling and melting points of alkanes gradually increase with increasing carbon chain length. All hydrocarbons are poorly soluble in water; liquid hydrocarbons are common organic solvents.

Chemical properties.

1. substitution reactions. The most characteristic of alkanes are free radical substitution reactions, during which a hydrogen atom is replaced by a halogen atom or some group.

Let us present the equations of the most typical reactions.

Halogenation:

$CH_4+Cl_2→CH_3Cl+HCl$.

In the case of an excess of halogen, chlorination can go further, up to the complete replacement of all hydrogen atoms by chlorine:

$CH_3Cl+Cl_2→HCl+(CH_2Cl_2)↙(\text"dichloromethane(methylene chloride)")$,

$CH_2Cl_2+Cl_2→HCl+(CHСl_3)↙(\text"trichloromethane(chloroform)")$,

$CHCl_3+Cl_2→HCl+(CCl_4)↙(\text"tetrachloromethane(carbon tetrachloride)")$.

The resulting substances are widely used as solvents and starting materials in organic synthesis.

2. Dehydrogenation (elimination of hydrogen). During the passage of alkanes over the catalyst ($Pt, Ni, Al_2O_3, Cr_2O_3$) at a high temperature ($400-600°C$), a hydrogen molecule is split off and an alkene is formed:

$CH_3—CH_3→CH_2=CH_2+H_2$

3. Reactions accompanied by the destruction of the carbon chain. All saturated hydrocarbons are burning with education carbon dioxide and water. Gaseous hydrocarbons mixed with air in certain proportions can explode. The combustion of saturated hydrocarbons is a free radical exothermic reaction that has a very great importance when using alkanes as fuel:

$CH_4+2O_2→CO_2+2H_2O+880 kJ.$

AT general view The combustion reaction of alkanes can be written as follows:

$C_(n)H_(2n+2)+((3n+1)/(2))O_2→nCO_2+(n+1)H_2O$

Thermal breakdown of hydrocarbons:

$C_(n)H_(2n+2)(→)↖(400-500°C)C_(n-k)H_(2(n-k)+2)+C_(k)H_(2k)$

The process proceeds according to the free radical mechanism. An increase in temperature leads to a homolytic rupture of the carbon-carbon bond and the formation of free radicals:

$R—CH_2CH_2:CH_2—R→R—CH_2CH_2+CH_2—R$.

These radicals interact with each other, exchanging a hydrogen atom, with the formation of an alkane molecule and an alkene molecule:

$R—CH_2CH_2+CH_2—R→R—CH=CH_2+CH_3—R$.

Thermal splitting reactions underlie the industrial process - hydrocarbon cracking. This process is the most important stage of oil refining.

When methane is heated to a temperature of $1000°C$, pyrolysis of methane begins - decomposition into simple substances:

$CH_4(→)↖(1000°C)C+2H_2$

When heated to a temperature of $1500°C$, the formation of acetylene is possible:

$2CH_4(→)↖(1500°C)CH=CH+3H_2$

4. Isomerization. When linear hydrocarbons are heated with an isomerization catalyst (aluminum chloride), substances with a branched carbon skeleton are formed:

5. Aromatization. Alkanes with six or more carbon atoms in the chain in the presence of a catalyst are cyclized to form benzene and its derivatives:

What is the reason that alkanes enter into reactions proceeding according to the free radical mechanism? All carbon atoms in alkane molecules are in the $sp^3$ hybridization state. The molecules of these substances are built using covalent nonpolar $C—C$ (carbon—carbon) bonds and weakly polar $C—H$ (carbon—hydrogen) bonds. They do not contain areas with high and low electron density, easily polarizable bonds, i.e. such bonds, the electron density in which can be shifted under the influence of external factors (electrostatic fields of ions). Therefore, alkanes will not react with charged particles, because bonds in alkane molecules are not broken by a heterolytic mechanism.

Alkenes

Unsaturated hydrocarbons include hydrocarbons containing multiple bonds between carbon atoms in molecules. Unlimited are alkenes, alkadienes (polyenes), alkynes. Cyclic hydrocarbons containing a double bond in the cycle (cycloalkenes), as well as cycloalkanes with a small number of carbon atoms in the cycle (three or four atoms) also have an unsaturated character. The property of unsaturation is associated with the ability of these substances to enter into addition reactions, primarily hydrogen, with the formation of saturated, or saturated, hydrocarbons - alkanes.

Alkenes are acyclic hydrocarbons containing in the molecule, in addition to single bonds, one double bond between carbon atoms and corresponding to the general formula $C_(n)H_(2n)$.

Its second name olefins- alkenes were obtained by analogy with unsaturated fatty acids (oleic, linoleic), the remains of which are part of liquid fats - oils (from lat. oleum- oil).

Homologous series of ethene

Unbranched alkenes make up the homologous series of ethene (ethylene):

$C_2H_4$ is ethene, $C_3H_6$ is propene, $C_4H_8$ is butene, $C_5H_(10)$ is pentene, $C_6H_(12)$ is hexene, etc.

Isomerism and nomenclature

For alkenes, as well as for alkanes, structural isomerism is characteristic. Structural isomers differ from each other in the structure of the carbon skeleton. The simplest alkene, which is characterized by structural isomers, is butene:

A special type of structural isomerism is the double bond position isomerism:

$CH_3—(CH_2)↙(butene-1)—CH=CH_2$ $CH_3—(CH=CH)↙(butene-2)—CH_3$

Almost free rotation of carbon atoms is possible around a single carbon-carbon bond, so alkane molecules can take on a wide variety of shapes. Rotation around the double bond is impossible, which leads to the appearance of another type of isomerism in alkenes - geometric, or cis-trans isomerism.

cis- isomers are different from trance- isomers by the spatial arrangement of fragments of the molecule (in this case, methyl groups) relative to the $π$-bond plane, and, consequently, by properties.

Alkenes are isomeric to cycloalkanes (interclass isomerism), for example:

The nomenclature of alkenes developed by IUPAC is similar to the nomenclature of alkanes.

1. Choice of the main circuit.

The formation of the name of a hydrocarbon begins with the definition of the main chain - the longest chain of carbon atoms in a molecule. In the case of alkenes, the main chain must contain a double bond.

2. Atom numbering of the main chain.

The numbering of the atoms of the main chain starts from the end to which the double bond is closest. For example, the correct connection name is:

$5$-methylhexene-$2$, not $2$-methylhexene-$4$, as might be expected.

If the position of the double bond cannot determine the beginning of the numbering of atoms in the chain, then it is determined by the position of the substituents, just as for saturated hydrocarbons.

3. Name formation.

The names of alkenes are formed in the same way as the names of alkanes. At the end of the name indicate the number of the carbon atom at which the double bond begins, and the suffix indicating that the compound belongs to the class of alkenes - -en.

For example:

Physical and chemical properties of alkenes

physical properties. The first three representatives of the homologous series of alkenes are gases; substances of the composition $C_5H_(10)$ - $C_(16)H_(32)$ are liquids; higher alkenes are solids.

The boiling and melting points naturally increase with increasing molecular weight connections.

Chemical properties.

Addition reactions. Recall that hallmark representatives unsaturated hydrocarbons- alkenes is the ability to enter into addition reactions. Most of these reactions proceed by the mechanism

1. hydrogenation of alkenes. Alkenes are able to add hydrogen in the presence of hydrogenation catalysts, metals - platinum, palladium, nickel:

$CH_3—CH_2—CH=CH_2+H_2(→)↖(Pt)CH_3—CH_2—CH_2—CH_3$.

This reaction proceeds at atmospheric and high blood pressure and does not require high temperature, tk. is exothermic. With an increase in temperature on the same catalysts, the reverse reaction, dehydrogenation, can occur.

2. Halogenation (addition of halogens). The interaction of an alkene with bromine water or a solution of bromine in an organic solvent ($CCl_4$) leads to a rapid discoloration of these solutions as a result of the addition of a halogen molecule to the alkene and the formation of dihalogen alkanes:

$CH_2=CH_2+Br_2→CH_2Br—CH_2Br$.

3.

$CH_3-(CH)↙(propene)=CH_2+HBr→CH_3-(CHBr)↙(2-bromopropene)-CH_3$

This reaction is subject to Markovnikov's rule:

When a hydrogen halide is added to an alkene, hydrogen is attached to a more hydrogenated carbon atom, i.e. the atom at which there are more hydrogen atoms, and the halogen - to the less hydrogenated one.

Hydration of alkenes leads to the formation of alcohols. For example, the addition of water to ethene underlies one of the industrial methods for obtaining ethyl alcohol:

$(CH_2)↙(ethene)=CH_2+H_2O(→)↖(t,H_3PO_4)CH_3-(CH_2OH)↙(ethanol)$

Note that a primary alcohol (with a hydroxo group at the primary carbon) is formed only when ethene is hydrated. When propene or other alkenes are hydrated, secondary alcohols are formed.

This reaction also proceeds in accordance with Markovnikov's rule - the hydrogen cation is attached to the more hydrogenated carbon atom, and the hydroxo group to the less hydrogenated one.

5. Polymerization. A special case of addition is the polymerization reaction of alkenes:

$nCH_2(=)↙(ethene)CH_2(→)↖(UV light,R)(...(-CH_2-CH_2-)↙(polyethylene)...)_n$

This addition reaction proceeds by a free radical mechanism.

6. Oxidation reaction.

Like any organic compounds, alkenes burn in oxygen to form $CO_2$ and $H_2O$:

$CH_2=CH_2+3O_2→2CO_2+2H_2O$.

In general:

$C_(n)H_(2n)+(3n)/(2)O_2→nCO_2+nH_2O$

Unlike alkanes, which are resistant to oxidation in solutions, alkenes are easily oxidized by the action of potassium permanganate solutions. In neutral or alkaline solutions, alkenes are oxidized to diols (dihydric alcohols), and hydroxyl groups are attached to those atoms between which a double bond existed before oxidation:

Alkadienes (diene hydrocarbons)

Alkadienes are acyclic hydrocarbons containing in the molecule, in addition to single bonds, two double bonds between carbon atoms and corresponding to the general formula $C_(n)H_(2n-2)$.

Depending on the mutual arrangement of double bonds, there are three types of dienes:

- alkadienes with cumulated arrangement of double bonds:

- alkadienes with conjugated double bonds;

$CH_2=CH—CH=CH_2$;

- alkadienes with isolated double bonds

$CH_2=CH—CH_2—CH=CH_2$.

All three types of alkadienes differ significantly from each other in structure and properties. The central carbon atom (an atom that forms two double bonds) in alkadienes with cumulated bonds is in the $sp$-hybridization state. It forms two $σ$-bonds lying on the same straight line and directed in opposite directions, and two $π$-bonds lying in perpendicular planes. $π$-bonds are formed due to unhybridized p-orbitals of each carbon atom. The properties of alkadienes with isolated double bonds are very specific, because conjugated $π$-bonds significantly affect each other.

p-Orbitals forming conjugated $π$-bonds make up practically a single system (it is called a $π$-system), because p-orbitals of neighboring $π$-bonds partially overlap.

Isomerism and nomenclature

Alkadienes are characterized by both structural isomerism and cis- and trans-isomerism.

Structural isomerism.

— isomerism of the carbon skeleton:

— isomerism of the position of multiple bonds:

$(CH_2=CH—CH=CH_2)↙(butadiene-1,3)$ $(CH_2=C=CH—CH_3)↙(butadiene-1,2)$

cis-, trans- isomerism (spatial and geometric)

For example:

Alkadienes are isomeric compounds of the classes of alkynes and cycloalkenes.

When forming the name of the alkadiene, the numbers of double bonds are indicated. The main chain must necessarily contain two multiple bonds.

For example:

Physical and chemical properties of alkadienes

physical properties.

Under normal conditions, propandien-1,2, butadiene-1,3 are gases, 2-methylbutadiene-1,3 is a volatile liquid. Alkadienes with isolated double bonds (the simplest of them is pentadiene-1,4) are liquids. Higher dienes are solids.

Chemical properties.

The chemical properties of alkadienes with isolated double bonds differ little from those of alkenes. Alkadienes with conjugated bonds have some special features.

1. Addition reactions. Alkadienes are capable of adding hydrogen, halogens, and hydrogen halides.

A feature of addition to alkadienes with conjugated bonds is the ability to attach molecules both in positions 1 and 2, and in positions 1 and 4.

The ratio of the products depends on the conditions and method of carrying out the corresponding reactions.

2.polymerization reaction. The most important property of dienes is the ability to polymerize under the influence of cations or free radicals. The polymerization of these compounds is the basis of synthetic rubbers:

$nCH_2=(CH—CH=CH_2)↙(butadiene-1,3)→((... —CH_2—CH=CH—CH_2— ...)_n)↙(\text"synthetic butadiene rubber")$ .

The polymerization of conjugated dienes proceeds as 1,4-addition.

In this case, the double bond turns out to be central in the link, and the elementary link, in turn, can take both cis-, and trance- configuration.

Alkynes

Alkynes are acyclic hydrocarbons containing in the molecule, in addition to single bonds, one triple bond between carbon atoms and corresponding to the general formula $C_(n)H_(2n-2)$.

Homologous series of ethine

Unbranched alkynes make up the homologous series of ethyne (acetylene):

$C_2H_2$ - ethyne, $C_3H_4$ - propyne, $C_4H_6$ - butyne, $C_5H_8$ - pentine, $C_6H_(10)$ - hexine, etc.

Isomerism and nomenclature

For alkynes, as well as for alkenes, structural isomerism is characteristic: isomerism of the carbon skeleton and isomerism of the position of the multiple bond. The simplest alkyne, which is characterized by structural isomers of the multiple bond position of the alkyne class, is butyne:

$CH_3—(CH_2)↙(butyn-1)—C≡CH$ $CH_3—(C≡C)↙(butyn-2)—CH_3$

The isomerism of the carbon skeleton in alkynes is possible, starting from pentyn:

Since the triple bond assumes a linear structure of the carbon chain, the geometric ( cis-, trans-) isomerism is not possible for alkynes.

The presence of a triple bond in hydrocarbon molecules of this class is reflected by the suffix -in, and its position in the chain - the number of the carbon atom.

For example:

Alkynes are isomeric compounds of some other classes. So, hexine (alkyne), hexadiene (alkadiene) and cyclohexene (cycloalkene) have the chemical formula $С_6Н_(10)$:

Physical and chemical properties of alkynes

physical properties. The boiling and melting points of alkynes, as well as alkenes, naturally increase with an increase in the molecular weight of the compounds.

Alkynes have a specific smell. They are more soluble in water than alkanes and alkenes.

Chemical properties.

Addition reactions. Alkynes are unsaturated compounds and enter into addition reactions. Basically, these are reactions. electrophilic addition.

1. Halogenation (addition of a halogen molecule). Alkyne is able to attach two halogen molecules (chlorine, bromine):

$CH≡CH+Br_2→(CHBr=CHBr)↙(1,2-dibromoethane),$

$CHBr=CHBr+Br_2→(CHBr_2-CHBr_2)↙(1,1,2,2-tetrabromoethane)$

2. Hydrohalogenation (addition of hydrogen halide). The addition reaction of hydrogen halide, proceeding according to the electrophilic mechanism, also proceeds in two stages, and at both stages the Markovnikov rule is fulfilled:

$CH_3-C≡CH+Br→(CH_3-CBr=CH_2)↙(2-bromopropene),$

$CH_3-CBr=CH_2+HBr→(CH_3-CHBr_2-CH_3)↙(2,2-dibromopropane)$

3. Hydration (addition of water). Of great importance for the industrial synthesis of ketones and aldehydes is the water addition reaction (hydration), which is called Kucherov's reaction:

4. hydrogenation of alkynes. Alkynes add hydrogen in the presence of metal catalysts ($Pt, Pd, Ni$):

$R-C≡C-R+H_2(→)↖(Pt)R-CH=CH-R,$

$R-CH=CH-R+H_2(→)↖(Pt)R-CH_2-CH_2-R$

Since the triple bond contains two reactive $π$ bonds, alkanes add hydrogen in steps:

1) trimerization.

When ethyne is passed over activated carbon, a mixture of products is formed, one of which is benzene:

2) dimerization.

In addition to trimerization of acetylene, its dimerization is also possible. Under the action of monovalent copper salts, vinylacetylene is formed:

$2HC≡CH→(HC≡C-CH=CH_2)↙(\text"butene-1-yn-3(vinylacetylene)")$

This substance is used to produce chloroprene:

$HC≡C-CH=CH_2+HCl(→)↖(CaCl)H_2C=(CCl-CH)↙(chloroprene)=CH_2$

polymerization of which produces chloroprene rubber:

$nH_2C=CCl-CH=CH_2→(...-H_2C-CCl=CH-CH_2-...)_n$

Alkyne oxidation.

Ethine (acetylene) burns in oxygen with the release of a very large amount of heat:

$2C_2H_2+5O_2→4CO_2+2H_2O+2600kJ$ The action of an oxy-acetylene torch is based on this reaction, the flame of which has a very high temperature (more than $3000°C$), which makes it possible to use it for cutting and welding metals.

In air, acetylene burns with a smoky flame, because. the carbon content in its molecule is higher than in the molecules of ethane and ethene.

Alkynes, like alkenes, decolorize acidified solutions of potassium permanganate; in this case, the destruction of the multiple bond occurs.

Reactions characterizing the main methods for obtaining oxygen-containing compounds

1. Hydrolysis of haloalkanes. You already know that the formation of halokenalkanes during the interaction of alcohols with hydrogen halides - reversible reaction. Therefore, it is clear that alcohols can be obtained by hydrolysis of haloalkanes- reactions of these compounds with water:

$R-Cl+NaOH(→)↖(H_2O)R-OH+NaCl+H_2O$

Polyhydric alcohols can be obtained by hydrolysis of haloalkanes containing more than one halogen atom in the molecule. For example:

2. Hydration of alkenes- the addition of water to the $π$-bond of the alkene molecule - is already familiar to you, for example:

$(CH_2=CH_2)↙(ethene)+H_2O(→)↖(H^(+))(C_2H_5OH)↙(ethanol)$

Hydration of propene leads, in accordance with Markovnikov's rule, to the formation of a secondary alcohol - propanol-2:

3. Hydrogenation of aldehydes and ketones. You already know that the oxidation of alcohols under mild conditions leads to the formation of aldehydes or ketones. Obviously, alcohols can be obtained by hydrogenation (hydrogen reduction, hydrogen addition) of aldehydes and ketones:

4. Alkene oxidation. Glycols, as already noted, can be obtained by oxidizing alkenes with an aqueous solution of potassium permanganate. For example, ethylene glycol (ethanediol-1,2) is formed during the oxidation of ethylene (ethene):

$CH_2=CH_2+[O]+H_2O(→)↖(KMnO_4)HO-CH_2-CH_2-OH$

5. Specific methods for obtaining alcohols. Some alcohols are obtained in ways characteristic only of them. Thus, methanol is produced in industry by the interaction of hydrogen with carbon monoxide (II) (carbon monoxide) at elevated pressure and high temperature on the surface of the catalyst (zinc oxide):

$CO+2H_2(→)↖(t,p,ZnO)CH_3-OH$

The mixture required for this reaction carbon monoxide and hydrogen, also called synthesis gas ($CO + nH_2O$), is obtained by passing water vapor over hot coal:

$C+H_2O(→)↖(t)CO+H_2-Q$

6. Fermentation of glucose. This method of obtaining ethyl (wine) alcohol has been known to man since ancient times:

$(C_6H_(12)O_6)↙(glucose)(→)↖(yeast)2C_2H_5OH+2CO_2$

Methods for obtaining aldehydes and ketones

Aldehydes and ketones can be obtained oxidation or alcohol dehydrogenation. Once again, we note that aldehydes can be obtained during the oxidation or dehydrogenation of primary alcohols, and ketones can be obtained from secondary alcohols:

Kucherov's reaction. From acetylene, as a result of the hydration reaction, acetaldehyde is obtained, from acetylene homologs - ketones:

When heated calcium or barium salts carboxylic acids a ketone and a metal carbonate are formed:

Methods for obtaining carboxylic acids

Carboxylic acids can be obtained by oxidation of primary alcohols of aldehydes:

Aromatic carboxylic acids are formed during the oxidation of benzene homologues:

Hydrolysis of various carboxylic acid derivatives also results in acids. So, during the hydrolysis of an ester, an alcohol and a carboxylic acid are formed. As mentioned above, acid-catalyzed esterification and hydrolysis reactions are reversible:

The hydrolysis of an ester under the action of an aqueous solution of alkali proceeds irreversibly, in this case, not an acid, but its salt is formed from the ester.

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A17. The main methods for obtaining hydrocarbons (in the laboratory). The main methods for obtaining oxygen-containing compounds (in the laboratory).

"> Obtaining alkanes

Industrial Ways:

1. Allocate from natural sources (natural and associated gases, oil, coal).
2. "> Hydrogenation of alkenes and unsaturated hydrocarbons.

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CO + 3H 2 → CH 4 + H 2 O

CO 2 + 4H 2 → CH 4 + 2H 2 O

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2. ">Hydrolysis of aluminum carbide:" xml:lang="en-US" lang="en-US">Al;vertical-align:sub">4 " xml:lang="en-US" lang="en-US">C;vertical-align:sub">3"> + 12 " xml:lang="en-US" lang="en-US">H;vertical-align:sub">2 " xml:lang="en-US" lang="en-US">O"> → 4 " xml:lang="en-US" lang="en-US">Al">(" xml:lang="en-US" lang="en-US">OH">) ;vertical-align:sub">3 "> + 3 " xml:lang="en-US" lang="en-US">CH;vertical-align:sub">4

;text-decoration:underline">Laboratory methods for obtaining methane homologues:

1. "> Decarboxylation of sodium salts of carboxylic acids (Dumas reaction). The resulting alkane contains one carbon atom less than the original salt.

" xml:lang="en-US" lang="en-US">CH;vertical-align:sub" xml:lang="en-US" lang="en-US">3" xml:lang="en-US" lang="en-US">COONa + NaOH → CH;vertical-align:sub" xml:lang="en-US" lang="en-US">4" xml:lang="en-US" lang="en-US"> + Na;vertical-align:sub" xml:lang="en-US" lang="en-US">2" xml:lang="en-US" lang="en-US">CO;vertical-align:sub" xml:lang="en-US" lang="en-US">3" xml:lang="en-US" lang="en-US">

1. "> Wurtz Synthesis (chain doubling); carried out in order to obtain alkanes with a longer carbon chain.

">2 " xml:lang="en-US" lang="en-US">CH;vertical-align:sub">3 " xml:lang="en-US" lang="en-US">Cl"> + 2 " xml:lang="en-US" lang="en-US">Na"> → " xml:lang="en-US" lang="en-US">C;vertical-align:sub">2 " xml:lang="en-US" lang="en-US">H;vertical-align:sub">6"> + 2 " xml:lang="en-US" lang="en-US">NaCl">

1. Electrolysis of sodium acetate:

electrolysis

2 CH 3 COONa + 2H 2 O → C2 H6 + 2CO2 + H2 + 2 NaOH

Obtaining alkenes

In the laboratory:

1. Dehydrohalogenation of haloalkanes is carried out with an alcohol solution of alkali:

CH 3 - CH 2 Cl + KOH (alcohol) → CH 2 = CH 2 + KCl + H 2 O

CH 3 - CH - CH 2 - CH 3 + KOH (alcohol) → CH 3 - CH \u003d CH - CH 3 + KI + H 2 O

Rule A.M. Zaitsev: "Hydrogen is split off from a less hydrogenated carbon atom."

2. Dehydration of alcohols proceeds in the presence of concentrated sulfuric acid or anhydrous aluminum oxide when heated (t> 150o C) with the formation of alkenes.

CH 3 - CH 2 - CH 2 OH → CH 3 - CH \u003d CH 2 + H 2 O

3. Dehalogenation of dihalogen derivatives is carried out using finely divided zinc or magnesium:

CH 3 - CH - CH 2 + Zn → CH 3 - CH \u003d CH 2 + ZnCl 2

Cl Cl

In industry:

1, The main way to obtain alkenes is the cracking of alkanes, leading to the formation of a mixture of low molecular weight alkenes and alkanes, which can be separated by distillation.

C5 H12 → C2 H4 + C3 H8 (or C3 H6 + C2 H6), etc.

2 Dehydrogenation of alkanes. (catalysts: Pt ; Ni ; AI 2 O 3 ; Cr 2 O 3 )

Ni, 450 – 5000 C

CH3 - CH3 → CH2 = CH2 + H2

550 - 6500 C

2CH 4 → CH 2 = CH2 + 2H2

3. Catalytic hydrogenation of alkynes (catalysts: Pt ; Ni ; Pd )

CH ≡ CH + H2 → CH2 = CH2

Obtaining cycloalkanes

1. action active metal for dihaloalkane:

t, p, Ni

Br - C H2 -C H2 -C H2 -Br + Mg → + Mg Br 2

1,3-dibromopropane

1. Hydrogenation of arenes (t, p, Pt)

C6 H6 + 3 H2 →

Obtaining alkynes

Acetylene:

a) methane method:

2CH4 C2 H2 + 3H2

b) hydrolysis of calcium carbide (laboratory method):

CaC 2 + 2H 2 O C 2 H 2 + Ca (OH) 2

CaO + 3C CaC 2 + CO

Due to the high energy consumption, this method is economically less profitable.

Synthesis of acetylene homologues:

a) catalytic dehydrogenation of alkanes and alkenes:

Сn H 2 n +2 C n H 2 n -2 + 2H 2

Сn H 2 n C n H 2 n -2 + H 2

b) dehydrohalogenation of dihaloalkanes with an alcohol solution of alkali (alkali and alcohol are taken in excess):

Cn H 2 n G2 + 2KOH (sp) C n H 2 n -2 + 2K G + 2H 2 O

Obtaining alkadienes

1. Dehydrogenation of alkanes contained in natural gas and refinery gases by passing them over a heated catalyst
   t, Cr 2 O 3 , Al 2 O 3

CH 3 -CH 2 -CH 2 -CH 3 → CH 2 \u003d CH-CH \u003d CH 2 + 2H 2
t, Cr 2 O 3 , Al 2 O 3

CH 3 -CH-CH 2 -CH 3 → CH 2 \u003d C-CH \u003d CH 2 + 2H 2

CH 3 CH 3

1. Dehydrogenation and dehydration of ethyl alcohol by passing alcohol vapor over heated catalysts (method of academician S.V. Lebedev):
   t, ZnO, Al 2 O 3

2CH 3 CH 2 OH → CH 2 \u003d CH–CH \u003d CH 2 + 2H 2 O + H 2

Getting arenas

Benzene

1. Trimerization of alkynes over activated carbon (Zelinsky):

Act. C, 600 C

3HCCH C6 H 6 (benzene)

1. In the laboratory by fusing salts of benzoic acid with alkalis:

C6 H5 - COOHa + Na OH → C6 H6 + Na 2 CO3

Benzene and homologues

1. During the coking of coal, coal tar is formed, from which benzene, toluene, xylenes, naphthalene and many other organic compounds are isolated.
2. Dehydrocyclization (dehydrogenation and cyclization) of alkanes in the presence of a catalyst:

Cr2O3

CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 C 6 H 6 + 4H 2

Hexane produces benzene, and heptane produces toluene.

1. Dehydrogenation of cycloalkanes

→ C6 H6 + 3 H2

1. Obtaining homologues - alkylation of benzene with haloalkanes or alkenes in the presence of anhydrous aluminum chloride:

AlCl 3

C 6 H 6 + C 2 H 5 Cl C 6 H 5 C 2 H 5 + HCl

chloroethane ethylbenzene

Getting limit monohydric alcohols

General methods

1. Hydration of alkenes (according to Markovnikov's rule):

t, H 2 SO 4

CH3 -CH \u003d CH2 + H-OH → CH3 -CH-CH3

OH (propanol-2)

1. Hydrolysis of haloalkanes under the action of an aqueous solution of alkali:

C 2 H 5 I + Na OH (aq.) → C 2 H 5 -O H + NaI

1. Recovery (hydrogenation) of aldehydes and ketones.

Hydrogenation of aldehydes produces primary alcohols:

t, Ni

CH3 -CH2 -CHO + H2 → CH3 -CH2 - CH2 -OH

propanol-1

When ketones are hydrogenated, secondary alcohols are formed:

t, Ni

CH3 -C-CH3 + H2 → CH3 -CH-CH3

O OH (propanol-2)

Specific methods of obtaining

1. Methanol - from synthesis gas:

t, p, cat

CO + 2H2 → CH3 OH

1. Ethanol - alcoholic fermentation of glucose (enzymatic):

C6 H12 O6 → 2C2 H5 OH + 2CO2

ethylene glycol

1. In the laboratory - the Wagner reaction.

Oxidation of ethylene with potassium permanganate in neutral environment leads to the formation of dihydric alcohol - ethylene glycol.

Simplified:

KMnO 4 , H 2 O

CH 2 \u003d CH 2 + HOH + → CH 2 - CH 2

OH OH

3 CH 2 \u003d CH 2 + 2KMnO 4 + 4H 2 O → 3 CH 2 - CH 2 + 2MnO 2 + 2KOH

OH OH

1. In industry - hydrolysis of 1,2-dichloroethane:

CH2 Cl - CH2 Cl + 2NaOH → CH2 (OH)-CH2 OH + 2NaCl

Glycerol

1. Fat hydrolysis:

1. From propene:

a) CH2 = CH-CH3 + Cl 2 → CH2 = CH-CH2 Cl

3-chloropropene-1

b) CH2 \u003d CH-CH2 Cl + NaOH (aq.) → CH2 \u003d CH-CH2 -OH + N aCl

allyl alcohol

c) CH2 = CH-CH2 -OH + H2 O2 → CH2 -CH-CH2

Obtaining phenols

1. Extraction from coal tar.
2. Hydrolysis of chlorobenzene:

C6 H5 -Cl + H2 O (steam) → C6 H5 -OH + HCl

1. Oxidation of isopropylbenzene (cumene) with atmospheric oxygen:

Getting ethers

1. Intermolecular dehydration of ethanol:

t, H2SO4

2C2 H5 OH → C2 H5 -O-C2 H5 + H2 O

1. The interaction of a metal alcoholate with halogen derivatives of alkanes:

C 2 H 5 I + C 2 H 5 ONa → C 2 H 5 -O-C 2 H 5 + NaI

Obtaining aldehydes

General way

1. Alcohol oxidation. Primary alcohols are oxidized to aldehydes, and secondary alcohols to ketones:

t, Cu

2C 2 H 5 OH + O 2 → 2CH 3 CHO + 2H 2 O

T , Cu

CH3 -CH-CH3 + O 2 → CH3 -C-CH3

OH (propanol-2) O

Specific ways

1. Formaldehyde is produced by the catalytic oxidation of methane:

CH 4 + O 2 → HC HO + H 2 O

1. Acetic aldehyde (acetaldehyde):

a) Kucherov reaction

H+, Hg 2+

HCCH + H2 O CH3 -CHO

b) catalytic oxidation of ethylene

2CH2 \u003d CH2 + O2 → 2CH3 -CHO

Obtaining carboxylic acids

General methods

1. Oxidation of aldehydes under the action of various oxidizing agents:

R-CHO + Ag 2 O (amm.) → R-C OOH + 2Ag ↓

" xml:lang="en-US" lang="en-US"> t

R-CHO + 2Cu(OH) 2 →R-COOH + Cu 2 O↓ + 2H 2 O

1. "> Catalytic oxidation - methane homologues are oxidized with a gap C-C chains and the formation of carboxylic acids:

"> 2 " xml:lang="en-US" lang="en-US">C;vertical-align:sub">4 " xml:lang="en-US" lang="en-US">H;vertical-align:sub">10">+ 5 " xml:lang="en-US" lang="en-US">O;vertical-align:sub">2"> → 4CH ;vertical-align:sub">3 " xml:lang="en-US" lang="en-US">COO">H+ 2 " xml:lang="en-US" lang="en-US">H;vertical-align:sub">2 " xml:lang="en-US" lang="en-US">O">

Specific ways

1. Formic acid is obtained by heating under pressure powdered sodium hydroxide and carbon monoxide, followed by treatment of the resulting sodium formate with a strong acid:

NaOH + CO → HCOONa

H 2 SO 4 + 2HCOONa → HCOO H + Na 2 SO 4

1. Acetic acid:

a) For food purposes, they are obtained by enzymatic fermentation (oxidation) of liquids containing alcohol (wine, beer):

enzymes

C 2 H 5 OH + O2 → CH 3 C OOH + H 2 O

b) In the laboratory from acetates:

2CH3 COONa + H 2 SO 4 → 2CH3 COO H + Na 2 SO 4

Obtaining esters

1. Esterification reaction when an acid and an alcohol are heated in the presence of sulfuric acid or other mineral acids. Isotopic studies have shown that in the esterification reaction, a hydrogen atom is separated from an alcohol molecule, and a hydroxyl group is separated from an acid molecule.

This reaction is reversible and obeys Le Chatelier's rule. To increase output

esters, it is necessary to remove the resulting water from the reaction medium.

CH3 -COOH + HOCH2 CH3 → CH3-CO-O-CH2 CH3 + H2 O

Getting soap

1. "> Alkaline hydrolysis (saponification of fats occurs irreversibly under the action of alkalis):

1. "> Neutralization of carboxylic acids obtained by catalytic oxidation of higher oil paraffins:

">2 C ;vertical-align:sub">32 ">H ;vertical-align:sub">66 "> + 5O ;vertical-align:sub">2 ">→ 4C ;vertical-align:sub" >15 ">H ;vertical-align:sub">31">COOH + 2H ;vertical-align:sub">2">O

"> palmitic acid

"> C ;vertical-align:sub">15 ">H ;vertical-align:sub">31 ">COOH + " xml:lang="en-US" lang="en-US">NaOH"> → C ;vertical-align:sub">15 ">H ;vertical-align:sub">31 ">COO " xml:lang="en-US" lang="en-US">Na">">+ N ;vertical-align:sub">2 " xml:lang="en-US" lang="en-US">O">

"> sodium palmitate (solid soap)

"> C ;vertical-align:sub">15 ">H ;vertical-align:sub">31 ">COOH + K " xml:lang="en-US" lang="en-US">OH"> → C ;vertical-align:sub">15 ">H ;vertical-align:sub">31 ">COO ">K ">+ H ;vertical-align:sub">2 " xml:lang="en-US" lang="en-US">O">

"> potassium palmitate (liquid soap)

Getting carbohydrates

1. Glucose - by hydrolysis of starch or cellulose:

(C6 H10 O5 )n + nH2 O nC6 H12 O6

1. Sucrose - from sugar beet and sugar cane.

Hydrocarbons are a very large class of organic compounds. They include several main groups of substances, among which almost every one is widely used in industry, everyday life, and nature. Of particular importance are halogenated hydrocarbons, which will be discussed in the article. They are not only of high industrial importance, but are also important raw materials for many chemical syntheses, obtaining medicines and other important compounds. We will pay special attention to the structure of their molecules, properties and other features.

Halogenated hydrocarbons: general characteristics

From the point of view of chemical science, this class of compounds includes all those hydrocarbons in which one or more hydrogen atoms are replaced by one or another halogen. This is a very broad category of substances, as they are of great industrial importance. Within a fairly short time, people have learned to synthesize almost all halogen derivatives of hydrocarbons, the use of which is necessary in medicine, the chemical industry, the food industry and everyday life.

The main method for obtaining these compounds is the synthetic route in the laboratory and industry, since practically none of them occurs in nature. Due to the presence of a halogen atom, they have a high reactivity. This largely determines the areas of their application in chemical syntheses as intermediate products.

Since there are many representatives of halogenated hydrocarbons, it is customary to classify them according to different criteria. It is based on both the structure of the chain and the multiplicity of bonds, and the difference in the halogen atoms and their position.

Halogen derivatives of hydrocarbons: classification

The first separation option is based on generally accepted principles that apply to everyone. The classification is based on the difference in the type of carbon chain, its cyclicity. On this basis, distinguish:

• saturated halogenated hydrocarbons;
• unsaturated;
• aromatic;
• aliphatic;
• acyclic.

The following division is based on the type of halogen atom and its quantitative content in the composition of the molecule. So, allocate:

• monoderivatives;
• derivatives;
• three-;
• tetra-;
• penta derivatives and so on.

If we talk about the type of halogen, then the name of the subgroup consists of two words. For example, a monochloro derivative, a triiodo derivative, a tetrabromohaloalkene, and so on.

There is also another classification option, according to which mainly halogen derivatives of saturated hydrocarbons are separated. This is the number of the carbon atom to which the halogen is attached. So, allocate:

• primary derivatives;
• secondary;
• tertiary and so on.

Each individual representative can be ranked according to all characteristics and determined full place in system organic compounds. So, for example, a compound with the composition CH 3 - CH 2 -CH=CH-CCL 3 can be classified as follows. It is an unsaturated aliphatic trichloro derivative of pentene.

The structure of the molecule

The presence of halogen atoms cannot but affect both the physical and chemical properties, and the general features of the structure of the molecule. The general formula for this class of compounds is R-Hal, where R is a free hydrocarbon radical of any structure, and Hal is a halogen atom, one or more. The bond between carbon and halogen is strongly polarized, as a result of which the molecule as a whole is prone to two effects:

• negative inductive;
• mesomeric positive.

In this case, the first of them is expressed much more strongly; therefore, the Hal atom always exhibits the properties of an electron-withdrawing substituent.

Otherwise, all structural features of the molecule are no different from those of ordinary hydrocarbons. The properties are explained by the structure of the chain and its branching, the number of carbon atoms, and the strength of aromatic features.

The nomenclature of halogen derivatives of hydrocarbons deserves special attention. What is the correct name for these connections? To do this, you need to follow a few rules.

1. The chain numbering starts from the edge closest to the halogen atom. If there is any multiple bond, then the counting starts from it, and not from the electron-withdrawing substituent.
2. The name Hal is indicated in the prefix, and the number of the carbon atom from which it departs should also be indicated.
3. The last step is the name of the main chain of atoms (or ring).

An example of a similar name: CH 2 \u003d CH-CHCL 2 - 3-dichloropropene-1.

The name can also be given according to In this case, the name of the radical is pronounced, and then the name of the halogen with the suffix -id. Example: CH 3 -CH 2 -CH 2 Br - propyl bromide.

Like other classes of organic compounds, halogenated hydrocarbons have a special structure. This allows many representatives to be designated by historical names. For example, halothane CF 3 CBrClH. The presence of three halogens at once in the composition of the molecule provides this substance with special properties. It is used in medicine, therefore, it is the historical name that is most often used.

Synthesis methods

Methods for obtaining halogen derivatives of hydrocarbons are quite diverse. There are five main methods for the synthesis of these compounds in the laboratory and industry.

1. Halogenation of conventional normal hydrocarbons. General scheme reactions: R-H + Hal 2 → R-Hal + HHal. The features of the process are as follows: with chlorine and bromine, ultraviolet irradiation is required, with iodine the reaction is almost impossible or very slow. The interaction with fluorine is too active, so this halogen cannot be used in its pure form. In addition, when halogenating aromatic derivatives, it is necessary to use special process catalysts - Lewis acids. For example, iron or aluminum chloride.
2. Obtaining halogen derivatives of hydrocarbons is also carried out by hydrohalogenation. However, for this, the starting compound must necessarily be an unsaturated hydrocarbon. Example: R=R-R + HHal → R-R-RHal. Most often, this is used to obtain chlorethylene or vinyl chloride, since this compound is an important raw material for industrial syntheses.
3. The effect of hydrohalogens on alcohols. The general form of the reaction: R-OH + HHal → R-Hal + H 2 O. A feature is the mandatory presence of a catalyst. Examples of process accelerators that can be used are phosphorus, sulfur, zinc or iron chlorides, sulphuric acid, solution in hydrochloric acid- Lucas reagent.
4. Decarboxylation of acid salts with an oxidizing agent. Another name for the method is the Borodin-Hunsdicker reaction. The bottom line is the removal of a carbon dioxide molecule from silver derivatives when exposed to an oxidizing agent - a halogen. As a result, halogen derivatives of hydrocarbons are formed. Reactions in general look like this: R-COOAg + Hal → R-Hal + CO 2 + AgHal.
5. Synthesis of haloforms. In other words, this is the production of trihalogen derivatives of methane. The easiest way to produce them is to treat acetone with an alkaline solution of halogens. As a result, the formation of haloform molecules occurs. In the same way, halogen derivatives of aromatic hydrocarbons are synthesized in industry.

Particular attention should be paid to the synthesis of unlimited representatives of the class under consideration. The main method is the treatment of alkynes with mercury and copper salts in the presence of halogens, which leads to the formation of a product with a double bond in the chain.

Halogen derivatives of aromatic hydrocarbons are obtained by halogenation reactions of arenes or alkylarenes into a side chain. These are important industrial products as they are used as insecticides in agriculture.

Physical Properties

Halogen derivatives of hydrocarbons directly depend on the structure of the molecule. At the boiling and melting points, state of aggregation influence the number of carbon atoms in the chain and possible branches to the side. The more of them, the higher the scores. In general, the physical parameters can be characterized in several points.

1. Aggregate state: the first lower representatives are gases, the next up to C 12 are liquids, above are solids.
2. Almost all representatives have a sharp unpleasant specific smell.
3. They are very poorly soluble in water, but they themselves are excellent solvents. They dissolve very well in organic compounds.
4. Boiling and melting points increase as the number of carbon atoms in the main chain increases.
5. All compounds, except for fluorine derivatives, are heavier than water.
6. The more branches in the main chain, the lower the boiling point of the substance.

It is difficult to identify many similarities in common, because the representatives differ greatly in composition and structure. Therefore, it is better to give values ​​for each specific compound from this series hydrocarbons.

Chemical properties

One of the most important parameters that must be taken into account in the chemical industry and synthesis reactions is the chemical properties of halogenated hydrocarbons. They are not the same for all representatives, since there are a number of reasons for the difference.

1. The structure of the carbon chain. The simplest substitution reactions (of the nucleophilic type) occur in secondary and tertiary haloalkyls.
2. The type of halogen atom is also important. The bond between carbon and Hal is strongly polarized, which makes it easy to break with the release of free radicals. However, the bond between iodine and carbon breaks most easily, which is explained by a regular change (decrease) in the bond energy in the series: F-Cl-Br-I.
3. The presence of an aromatic radical or multiple bonds.
4. The structure and branching of the radical itself.

In general, halogenated alkyls are best reacted by nucleophilic substitution reactions. After all, a partially positive charge is concentrated on the carbon atom after breaking the bond with the halogen. This allows the radical as a whole to become an acceptor of electronegative particles. For example:

• HE - ;
• SO 4 2- ;
• NO 2 - ;
• CN - and others.

This explains the fact that one can go from halogen derivatives of hydrocarbons to almost any class of organic compounds, it is only necessary to choose the appropriate reagent that will provide the desired functional group.

In general, we can say that the chemical properties of halogen derivatives of hydrocarbons are the ability to enter into the following interactions.

1. With nucleophilic particles of various kinds - substitution reactions. The result can be: alcohols, simple and nitro compounds, amines, nitriles, carboxylic acids.
2. Elimination or dehydrohalogenation reactions. As a result of exposure to an alcoholic solution of alkali, a hydrogen halide molecule is cleaved. This is how an alkene is formed, low molecular weight by-products - salt and water. Reaction example: CH 3 -CH 2 -CH 2 -CH 2 Br + NaOH (alcohol) →CH 3 -CH 2 -CH \u003d CH 2 + NaBr + H 2 O. These processes are one of the main methods for the synthesis of important alkenes. The process is always accompanied by high temperatures.
3. normal structure according to the Wurtz synthesis method. The essence of the reaction is the effect on a halogen-substituted hydrocarbon (two molecules) with metallic sodium. As a strongly electropositive ion, sodium accepts halogen atoms from the compound. As a result, the liberated hydrocarbon radicals are interconnected by a bond, forming an alkane of a new structure. Example: CH 3 -CH 2 Cl + CH 3 -CH 2 Cl + 2Na → CH 3 -CH 2 -CH 2 -CH 3 + 2NaCl.
4. Synthesis of homologues of aromatic hydrocarbons by the method of Friedel-Crafts. The essence of the process is the action of haloalkyl on benzene in the presence of aluminum chloride. As a result of the substitution reaction, the formation of toluene and hydrogen chloride occurs. In this case, the presence of a catalyst is necessary. In addition to benzene itself, its homologues can also be oxidized in this way.
5. Preparation of Greignard's liquid. This reagent is a halogen-substituted hydrocarbon with a magnesium ion in the composition. Initially, metallic magnesium in ether acts on the haloalkyl derivative. As a result, a complex compound with the general formula RMgHal is formed, called the Greignard reagent.
6. Reduction reactions to an alkane (alkene, arene). Carried out when exposed to hydrogen. As a result, a hydrocarbon and a by-product, hydrogen halide, are formed. General example: R-Hal + H 2 → R-H + HHal.

These are the main interactions that halogen derivatives of hydrocarbons of various structures can easily enter into. Of course, there are specific reactions that should be considered for each individual representative.

Isomerism of molecules

The isomerism of halogen derivatives of hydrocarbons is a completely natural phenomenon. After all, it is known that the more carbon atoms in the chain, the higher the number of isomeric forms. In addition, unsaturated representatives have multiple bonds, which also causes the appearance of isomers.

Two main varieties of this phenomenon can be distinguished for this class of compounds.

1. Isomerism of the carbon skeleton of the radical and the main chain. This also includes the position of the multiple bond, if it exists in the molecule. As with simple hydrocarbons, starting from the third representative, formulas of compounds that have identical molecular but different structural formula expressions can be written. Moreover, for halogen-substituted hydrocarbons, the number of isomeric forms is an order of magnitude higher than for their corresponding alkanes (alkenes, alkynes, arenes, and so on).
2. The position of the halogen in the molecule. Its place in the name is indicated by a number, and even if it changes by only one, then the properties of such isomers will already be completely different.

We are not talking about spatial isomerism here, since halogen atoms make this impossible. Like all other organic compounds, haloalkyl isomers differ not only in structure, but also in physical and chemical characteristics.

Derivatives of unsaturated hydrocarbons

There are, of course, many such connections. However, we are interested in halogen derivatives of unsaturated hydrocarbons. They can also be divided into three main groups.

1. Vinyl - when the Hal atom is located directly at the carbon atom of the multiple bond. Molecule example: CH 2 =CCL 2.
2. With isolated position. The halogen atom and the multiple bond are located in opposite parts of the molecule. Example: CH 2 =CH-CH 2 -CH 2 -Cl.
3. Allyl derivatives - the halogen atom is located to the double bond through one carbon atom, that is, it is in the alpha position. Example: CH 2 =CH-CH 2 -CL.

Of particular importance is a compound such as vinyl chloride CH 2 =CHCL. It is capable of forming important products such as insulating materials, waterproof fabrics, and so on.

Another representative of unsaturated halogen derivatives is chloroprene. Its formula is CH₂=CCL-CH=CH₂. This compound is a feedstock for the synthesis of valuable types of rubber, which are distinguished by fire resistance, long service life, and poor gas permeability.

Tetrafluoroethylene (or Teflon) is a polymer that has high-quality technical parameters. It is used for the manufacture of a valuable coating of technical parts, utensils, various appliances. Formula - CF 2 \u003d CF 2.

Aromatic hydrocarbons and their derivatives

Aromatic compounds are those compounds that contain a benzene ring. Among them there is also a whole group of halogen derivatives. Two main types can be distinguished according to their structure.

1. If the Hal atom is bonded directly to the nucleus, that is, the aromatic ring, then the compounds are called haloarenes.
2. The halogen atom is not connected to the ring, but to the side chain of atoms, that is, the radical that goes to the side branch. Such compounds are called arylalkyl halides.

Among the substances under consideration, several representatives of the greatest practical importance can be named.

1. Hexachlorobenzene - C 6 Cl 6. Since the beginning of the 20th century, it has been used as a strong fungicide, as well as an insecticide. It has a good disinfecting effect, so it was used for dressing seeds before sowing. It has an unpleasant odor, the liquid is quite caustic, transparent, and can cause lacrimation.
2. Benzyl bromide C 6 H 5 CH 2 Br. It is used as an important reagent in the synthesis of organometallic compounds.
3. Chlorobenzene C 6 H 5 CL. Liquid colorless substance with a specific odor. It is used in the production of dyes, pesticides. It is one of the best organic solvents.

Industrial use

Halogen derivatives of hydrocarbons are widely used in industry and chemical syntheses. We have already spoken about unsaturated and aromatic representatives. Now let us designate in general the areas of use of all compounds of this series.

1. In construction.
2. as solvents.
3. By production of fabrics, rubber, rubbers, dyes, polymeric materials.
4. For the synthesis of many organic compounds.
5. Fluorine derivatives (freons) are refrigerants in refrigeration units.
6. Used as pesticides, insecticides, fungicides, oils, drying oils, resins, lubricants.
7. They go to the manufacture of insulating materials, etc.

Physical Properties. Under normal conditions, the first four members of the homologous series of alkanes (C 1 - C 4) are gases. Normal alkanes from pentane to heptadecane ( C5 - C17 ) - liquids, starting from C 18 and above - solids. As the number of carbon atoms in the chain increases, i.e. with an increase in the relative molecular weight, the boiling and melting points of alkanes increase. For the same number of carbon atoms in a molecule, branched alkanes have lower boiling points than normal alkanes.

Alkanespractically insoluble in water, since their molecules are low-polar and do not interact with water molecules, they dissolve well in non-polar organic solvents such as benzene, carbon tetrachloride, etc. Liquid alkanes mix easily with each other.

The main natural sources of alkanes are oil and natural gas. Various oil fractions contain alkanes from C 5 H 12 up to C 30 H 62. Natural gas consists of methane (95%) with an admixture of ethane and propane.

From synthetic methods for obtaining alkanes the following can be distinguished:

one . Obtaining from unsaturated hydrocarbons. The interaction of alkenes or alkynes with hydrogen ("hydrogenation") occurs in the presence of metal catalysts (/>Ni, Pd ) at
heating:

CH s - C ≡CH+ 2H 2 → CH 3 -CH 2 -CH 3.

2. Getting from halogen-conducting. When monohalogenated alkanes are heated with sodium metal, alkanes with twice the number of carbon atoms are obtained (Wurtz reaction): />

C 2 H 5 Br + 2 Na + Br - C 2 H 5 → C 2 H 5 - C 2 H 5 + 2 NaBr.

A similar reaction is not carried out with two different halogenated alkanes, since this produces a mixture of three different alkanes

3 . Obtaining from salts of carboxylic acids. When anhydrous salts of carboxylic acids are fused with alkalis, alkanes are obtained containing one less carbon atom compared to the carbon chain of the original carboxylic acids: />

4. Obtaining methane. In an electric arc burning in a hydrogen atmosphere, a significant amount of methane is formed: />

C + 2H 2 → CH 4 .

The same reaction occurs when carbon is heated in a hydrogen atmosphere to 400–500°C at elevated pressure in the presence of a catalyst.

In laboratory conditions, methane is often obtained from aluminum carbide:

A l 4 C 3 + 12H 2 O \u003d ZSN 4 + 4A l (OH) 3 .

Chemical properties. Under normal conditions, alkanes are chemically inert. They are resistant to the action of many reagents: they do not interact with concentrated sulfuric and nitric acids, with concentrated and molten alkalis, they are not oxidized by strong oxidizing agents - potassium permanganateKMn About 4 etc.

The chemical stability of alkanes is due to the high strengths-C-C connections and C-H, as well as their non-polarity. Nonpolar C-C and C-H bonds in alkanes are not prone to ionic cleavage, but are capable of cleaving homolytically under the action of active free radicals. Therefore, alkanes are characterized by radical reactions, as a result of which compounds are obtained where hydrogen atoms are replaced by other atoms or groups of atoms. Therefore, alkanes enter into reactions proceeding according to the mechanism of radical substitution, denoted by the symbol S R ( from English, substitution radicalic). According to this mechanism, hydrogen atoms are most easily replaced at tertiary, then at secondary and primary carbon atoms.

1. Halogenation. When alkanes react with halogens (chlorine and bromine) under the action of UV radiation or high temperature, a mixture of products from mono- to polyhalogenated alkanes. The general scheme of this reaction is shown using methane as an example: />

b) Chain growth. The chlorine radical takes away a hydrogen atom from the alkane molecule:

Cl+ CH 4 →HC/>l + CH 3

In this case, an alkyl radical is formed, which takes away the chlorine atom from the chlorine molecule:

CH 3 + C l 2 → CH 3 C l + C l·

These reactions are repeated until chain termination occurs in one of the following reactions:

Cl· + Cl→ C l /> 2, CH 3 + CH 3 → C 2 H 6, CH 3 + Cl· → CH 3 С l ·

Overall reaction equation:

	hv
CH 4 + Cl 2	→	CH 3 Cl + Hcl.

The resulting chloromethane can be subjected to further chlorination, giving a mixture of products CH 2 Cl 2, CHCl 3, SS l 4 according to the scheme (*).

The development of the theory of chain free radical reactions is closely connected with the name of an outstanding Russian scientist, laureate Nobel Prize N.I. Semenov (1896-1986).

2. Nitration (Konovalov reaction). Under the action of diluted nitric acid on alkanes at 140 ° C and low pressure, a radical reaction proceeds: />

In radical reactions (halogenation, nitration), first of all, hydrogen atoms are mixed at the tertiary, then at the secondary and primary carbon atoms.This is explained by the fact that the bond of the tertiary carbon atom with hydrogen is most easily broken homolytically (bond energy 376 kJ / mol), then the secondary one (390 kJ / mol) and only then the primary one (415 kJ / mol).

3. Isomerization. Under certain conditions, normal alkanes can be converted into branched-chain alkanes: />

4. Cracking is a hemolytic rupture of C-C bonds, which occurs when heated and under the action of catalysts.
When higher alkanes are cracked, alkenes and lower alkanes are formed; when methane and ethane are cracked, acetylene is formed: />

C/> 8 H 18 → C 4 H 10 + C 4 H 8,/>

2CH 4 → C 2 H 2 + ZH 2,

C 2 H 6 → C 2 H 2 + 2H 2.

These reactions are of great industrial importance. In this way, high-boiling oil fractions (fuel oil) are converted into gasoline, kerosene and other valuable products.

5. Oxidation. With the mild oxidation of methane with atmospheric oxygen in the presence of various catalysts, methyl alcohol, formaldehyde, and formic acid can be obtained:

Soft catalytic oxidation of butane with atmospheric oxygen is one of the industrial methods for producing acetic acid:

t°
2 C 4/> H/> 10 + 5 O/> 2 → 4 CH/> 3 COOH/> + 2H 2 O .
cat

In air, alkanes burn to CO 2 and H 2 O: />

C n H 2 n +2 + (Z n+ 1) / 2O 2 \u003d n CO 2 + (n + 1) H 2 O.