Halogenated hydrocarbons: preparation, chemical properties, application. Methods for obtaining organic substances Laboratory methods for obtaining hydrocarbons

The production of organic compounds belonging to various classes is the main task of organic synthesis, both basic and fine. Many production methods are based on named reactions, the conditions for which must be remembered, since in organic chemistry it is the conditions that determine the resulting reaction product. In general, all reactions underlying the production of organic substances can be divided into the following types:

1. Reactions aimed at chain extension (constructive reactions), for example, alkylation, polymerization, (poly)condensation

2. Reactions aimed at shortening the carbon chain (cleavage reactions)

3. Reactions of introduction, removal or interconversion of functional groups

4. Reactions of formation of multiple bonds

5. Cyclization and aromatization reactions

Below, as reference material, we present basic methods obtaining hydrocarbons and their main derivatives - alcohols, aldehydes, ketones, carboxylic acids, amines, nitro- and halogen derivatives. Preparation methods will be discussed in detail by class of compounds in separate topics.

Methods for obtaining alkanes

1. Synthesis of symmetrical saturated hydrocarbons (extension of the hydrocarbon chain) by the action of metallic sodium on alkyl halides ( Wurtz reaction)

C 2 H 5 Br + CH 3 Br + 2 Na → C 3 H 8 +2 NaBr

2. Reduction of unsaturated hydrocarbons (hydrogenation of a double bond):

H 3 C − CH = CH 2 + H 2 → H 3 C − CH 2 − CH 3

3. Production of methane by fusion of salts of carboxylic acids with solid alkali:

t 0

CH 3 COONa + NaOH → Na 2 CO 3 + CH 4

4. Production of methane - hydrolysis of aluminum carbide (by the interaction of aluminum carbide with water):

Al 4 C 3 +12 H 2 O→ 4 Al (OH) 3 +3 CH 4

5. Rectification (direct distillation) of oil is discussed in detail in the topic “Principles of processing and use of fossil fuels”

Methods for preparing alkenes

1. Dehydrohalogenation (the effect of alcohol solutions of alkalis on monohalogen derivatives of hydrocarbons)

Alcohol NaOH

H 3 C − CH 2 − CH 2 Br→ H 3 C − CH = CH 2 + NaBr + H 2 O

2. Dehydration of alcohols (action of water-removing agents on alcohols):

3. Dehalogenation (the effect of metallic Zn or Mg on dihalogen derivatives with two halogen atoms at neighboring atoms):

4. Hydrogenation of acetylene hydrocarbons over catalysts with reduced activity (Fe)

3-methylbutyne-1 3-methylbutene-1

5. Pyrolysis (dehydrogenation) of alkanes (ethane) (see paragraph 2 "Methods for obtaining alkynes")

Methods for producing alkynes

Acetylene production:

1. Methane pyrolysis - intermolecular dehydrogenation (industrial method):

1500 ∘ C

H − CH 3 + H 3 C − H→ H − C ≡ C − H + 2 H 2

2. Pyrolysis (dehydrogenation) of ethane or ethylene (industrial method)

T0 C t 0 C

H 3 C − CH 3 → H 2 C = CH 2 + H 2 → H − C ≡ C − H + H 2

3. Hydrolysis of calcium carbide (reaction of calcium carbide with water):

CaC 2 + 2 H 2 O → HC ≡ CH + Ca (OH) 2

Preparation of acetylene homologues

1. Dehydrohalogenation (the effect of an alcohol solution of alkali on dihaloalkanes (alkali and alcohol are taken in excess):

2. Chain extension (alkylation of acetylenides) when acetylenides are treated with alkyl halides:

Methods for obtaining alkadienes

General methods for preparing dienes are similar to methods for producing alkenes.

1. Catalytic two-stage dehydrogenation of alkanes (through the stage of formation of alkenes). In this way, divinyl is produced industrially from butane contained in oil refining gases and associated gases:

In industry, isoprene is obtained by catalytic dehydrogenation of isopentane (2-methylbutane):

2. Synthesis of butadiene (divinyl) from ethyl alcohol (Lebedev reaction):

3. Dehydration of glycols (dihydric alcohols, or alkanediols):

4. Dehydrohalogenation of vicinal dihalogen derivatives in the presence of an alcoholic alkali solution:

Methods for obtaining benzene and its homologues (aromatic hydrocarbons)

The main methods for producing aromatic hydrocarbons are based either on cyclization processes followed by dehydrogenation; if there are more than six carbon atoms in the hydrocarbon chain, besol homologues with a side chain are formed. The process of trimerization of acetylene is used in the synthesis of benzene and thereby confirms its structure.

1. Dehydrogenation of cyclohexane (production of benzene)

2. Trimerization of acetylene (production of benzene) Zelinsky's reaction

3. Reforming (oil aromatization)

4. Coking of coal - heating without air access to 1000°C. A mixture of volatile substances, coal tar and a solid residue - coke - is formed. Resin is a liquid mixture of organic substances, from which many organic compounds are isolated, including arenes.

Methods for producing alcohols:

saturated monohydric, glycols, phenols

1. Alkaline hydrolysis of monohalogen derivatives of alkanes (nucleophilic substitution)

bromoethane ethanol

2. Hydration of ethylene and unsymmetrical alkenes (electrophilic addition) by Markovnikov's rule

3. Reduction (hydrogenation) of aldehydes (primary alcohols) and ketones (secondary alcohols)

ethanal

isopropyl dimethyl ketone

(acetone) alcohol

4. Alcoholic fermentation of plant materials containing carbohydrates:

C 6 H 12 O 6 → 2 C 2 H 5 OH + 2 CO 2 + 23.5 ⋅ 10 4 J

Preparation of glycols (dihydric saturated alcohols)

1. Oxidation of a double bond (mild oxidation only!) Wagner reaction:

Please note that when exposed to harsh oxidizing agents (an acidified solution of potassium peramangate or ozone), carbonyl compounds (carboxylic acids and aldehydes) are formed, since the reaction proceeds with discontinuity andσ - π -bonds.

Preparation of phenol (aromatic alcohol)

1. Cumene method (main industrial method)

2. Alkaline hydrolysis of chlorobenzene

3. Isolation from coal tar - a product of coking coal.

Methods for obtaining aldehydes and ketones

In the class of oxygen-containing hydrocarbons, aldehydes occupy an intermediate position in the genetic chain: alcohols - aldehydes - acids. Therefore, the main methods of production are based on the reduction of acids or the oxidation of alcohols.

1. Reduction (dehydrogenation) of alcohols: primary - to aldehydes, secondary - to ketones

ethanol ethanal

propanol-2 propanone-2 (acetone)

2. Oxidation of alcohols (conditional oxidizing agent - CuO, KMnO4 , air oxygen in the presence of a catalyst - Pt, Cu): primary - to aldehydes, secondary - to ketones

ethanol acetaldehyde

primary alcohol

isopropanol dimethyl ketone

secondary alcohol

3. Selective reduction of carboxylic acids

4. Reduction (hydrogenation) of acid chlorides according to Rosenmund(catalyst - platinum black, palladium)

5. Dry distillation of calcium and barium salts of monobasic acids: for all acids - ketones; for formic acid - aldehyde.

IN industry aldehydes are obtained in the following ways:

a) catalytic oxidation of alkanes (methane):

b) catalytic oxidation of ethylene with atmospheric oxygen ( Wacker process):

c) hydration of acetylene in the presence of mercury salts ( Kucherov's reaction):

Methods for obtaining carboxylic acids

Carboxylic acids are the last link in the oxidative chain “alcohols - aldehydes - acids”, therefore the methods for their preparation are based on oxidation reactions.

IN industry carboxylic acids are obtained by mild catalytic oxidation of alkanes, alcohols and aldehydes with atmospheric oxygen. Platinum, palladium, tin salts, etc. are used as catalysts; reactions are carried out at normal pressure and 200 0 C . Oxidation of aldehydes occurs most easily without additional heating.

1. Oxidation of alkanes:

2. Oxidation of alcohols:

3. Oxidation of aldehydes:

By specific methods synthesis of the simplest carboxylic acids (formic and acetic acids) are:

1. Synthesis of acetic acid by catalytic formylation of methanol (tungsten oxide catalyst, temperature 400 ∘ C pressure

2. Synthesis of formic acid from carbon monoxide and sodium hydroxide by heating, followed by an exchange reaction with sulfuric acid:

3. Synthesis of formic acid from carbon monoxide and water vapor (copper salt catalyst, sulfuric or phosphoric acid):

P, t 0 C , kat

CO + H 2 O → HCOOH

Isolation of hydrocarbons from natural raw materials

Sources of saturated hydrocarbons are oil And natural gas.

The main component of natural gas is the simplest hydrocarbon, methane, which is used directly or processed. Oil extracted from the depths of the earth is also subjected to processing, rectification, and cracking.

Most hydrocarbons are obtained from the processing of oil and other natural resources. But a significant amount of valuable hydrocarbons are obtained artificially, using synthetic methods.

Availability isomerization catalysts accelerates the formation of hydrocarbons with a branched skeleton from linear hydrocarbons:

The addition of catalysts allows one to slightly reduce the temperature at which the reaction occurs.

Hydrogenation (addition of hydrogen) of alkenes

As a result cracking a large number of unsaturated hydrocarbons with a double bond - alkenes - are formed. You can reduce their number by adding to the system hydrogen And hydrogenation catalysts- metals (platinum, palladium, nickel):

Cracking in the presence of hydrogenation catalysts with the addition of hydrogen is called reduction cracking. Its main products are saturated hydrocarbons.

Thus, increase in pressure during cracking(high-pressure cracking) allows you to reduce the amount of gaseous (CH 4 - C 4 H 10) hydrocarbons and increase the content of liquid hydrocarbons with a chain length of 6-10 carbon atoms, which form the basis of gasoline.

These were industrial methods for producing alkanes, which are the basis for the industrial processing of the main hydrocarbon raw material - oil.

Now let's look at several laboratory methods for producing alkanes.

Heating the sodium salt of acetic acid (sodium acetate) with an excess of alkali causes elimination of the carboxyl group and methane formation:

If instead of sodium acetate you take sodium propionate, then ethane is formed, from sodium butanoate - propane, etc.

At interaction of haloalkanes with the alkali metal sodium Saturated hydrocarbons and alkali metal halide are formed, for example:

Effect of an alkali metal on a mixture of halocarbons(e.g. bromoethane and bromomethane) will result in the formation of a mixture of alkanes (ethane, propane and butane).

The reaction on which the Wurtz synthesis is based proceeds well only with halogen alkanes, in the molecules of which a halogen atom is attached to a primary carbon atom.

When processing certain carbides containing carbon in the oxidation state -4 (for example, aluminum carbide), methane is formed by water:

Main methods for producing oxygen-containing compounds

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

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

Addition of water via the π bond of an alkene molecule, for example:

Leads, in accordance with Markovnikov’s rule, to the formation of a secondary alcohol - propanol-2:

Hydrogenation of aldehydes and ketones

Oxidation of alcohols under mild conditions leads to the formation of aldehydes or ketones. It is obvious that alcohols can be obtained by hydrogenation (reduction with hydrogen, addition of hydrogen) of aldehydes and ketones:

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

Specific methods for producing alcohols

1. Some alcohols are obtained using methods that are characteristic only of them. Thus, methanol is produced in industry reaction of hydrogen with carbon monoxide (II)(carbon monoxide) at elevated pressure and high temperature on the surface of the catalyst (zinc oxide):

The mixture of carbon monoxide and hydrogen required for this reaction, also called “synthesis gas,” is obtained by passing water vapor over hot coal:

2. Glucose fermentation. This method of producing ethyl (wine) alcohol has been known to man since ancient times:

Methods for producing aldehydes and ketones

1. Aldehydes and ketones can be obtained by oxidation or dehydrogenation of alcohols. At oxidation or dehydrogenation of primary alcohols aldehydes can be obtained, and secondary alcohols- ketones:

2. . As a result of the reaction, acetylene produces acetaldehyde, and ketones are obtained from acetylene homologues:

3. When heating calcium or barium salts of carboxylic acids ketone and metal carbonate are formed:

Methods for producing carboxylic acids

1. Carboxylic acids can be obtained oxidation of primary alcohols or aldehydes:

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

3. Hydrolysis of various carboxylic acid derivatives also leads to the production of acids. Thus, the hydrolysis of an ester produces an alcohol and a carboxylic acid. Acid-catalyzed esterification and hydrolysis reactions are reversible:

4. Hydrolysis of ester by aqueous alkali solution proceeds irreversibly, in this case, not an acid, but its salt is formed from the ester:

Reference material for taking the test:

Mendeleev table

Solubility table

Hydrocarbons whose carbon atoms are linked by single bonds are called saturated or saturated hydrocarbons.

general description

Saturated hydrocarbons include acyclic (alkanes) and carbocyclic (cycloalkanes) compounds. They differ in spatial structure and number of atoms.

A series of substances that are similar in structure and chemical properties, but differ in the number of atoms, is called homologous. Substances that are part of a homologous series are called homologues.

Alkanes are a homologous series of methane CH4.

Cycloalkanes or naphthenes are a homologous series of cyclopropane. A general description of saturated hydrocarbons is presented in the table.

Sign	Alkanes	Cycloalkanes
General formula
Molecule shape	Linear, branched	Cyclic in the form of a triangle, square, pentagon, hexagon
Examples of homologues	CH 4 - methane	C 3 H 6 - cyclopropane
	C 2 H 6 - ethane	C 4 H 8 - cyclobutane
	C 3 H 8 - propane	C 5 H 10 - cyclopentane
	C 4 H 10 - butane	C 6 H 12 - cyclohexane
	C 5 H 12 - pentane	C 7 H 14 - cycloheptane
	C 6 H 14 - hexane	C 8 H 16 - cyclooctane
	C 7 H 16 - heptane	C 9 H 18 - cyclononane
		C 10 H 20 - cyclodecane
	C 9 H 20 - nonane	C 11 H 22 - cycloundecane
		C 12 H 24 - cyclododecane

Compounds that have the same number of atoms but different structures are called isomers. All alkanes, starting with butane, have isomers. The prefix iso- (isobutane, isopentane, isohexane) is added to the name. The formula remains the same.

Rice. 1. Structural formula of butane and isobutane.

Cycloalkanes are characterized by three types of isomerism:

• spatial- location relative to the plane of the cycle;
• carbon- accession of additional groups to the CH 2 group;
• interclass- formation of isomers with alkenes.

The name of the substance changes depending on the group being added. For example, methylcyclopropane has a cyclic structure in the form of a triangle with a methyl (CH 3) attached. The name "1,2-dimethylcyclopentane" indicates a cyclic structure with two methyl molecules attached. The numbers indicate which corners of the pentagon the methyl is attached to.

In the corners of the figure of cycloalkanes there is always a CH 2 group, so it is often not written down, but simply drawn. The number of angles indicates the number of carbon atoms. Additional groups are added to the corners through a stroke.

Rice. 2. Examples of graphic formulas of cycloalkanes.

Receipt

There are industrial and laboratory methods for producing alkanes. In industry:

• separation from oil, gas, coal;
• gasification of solid fuel: C + 2H 2 → CH 4.

In the laboratory:

• hydrolysis of aluminum carbide:

  Al 4 C 3 + 12H 2 O → 4Al(OH) 3 + 3CH 4;

• substitution reaction:

  2CH 3 Cl + 2Na → CH 3 -CH 3 + 2NaCl;

• exchange reaction:

  CH 3 COONa + NaOH → Na 2 CO 3 + CH 4.

Cycloalkanes are obtained by isolation from natural sources - oil, gas, as well as by dehydrogenation of alkanes and hydrogenation of arenes:

• C 6 H 14 ↔ C 6 H 12 + H 2;
• C 6 H 6 + 3H 2 → C 6 H 12.

Properties

Alkanes and cycloalkanes have similar chemical properties. These are low-active substances that react only under additional conditions - heat, pressure. Reactions of saturated hydrocarbons:

• combustion:

  CH 4 + 2O 2 → CO 2 + 2H 2 O + Q;

• substitution (e.g. halogenation):

  CH 4 + Cl 2 → CH 3 Cl + HCl;

• accession:

  C6H12 + H2 → C6H14;

• decomposition:

  C 6 H 12 → C 6 H 6 + 3H 2 .

Rice. 3. Combustion of methane.

With an increase in the molecular weight of saturated hydrocarbons and, accordingly, the number of carbon atoms in homologous series, the boiling point of the substances increases. Cycloalkanes boil and melt at higher temperatures than alkanes. Methane, ethane, propane, butane are gases. Substances containing 5-15 carbon atoms (from C 5 H 12 to C 15 H 32) are liquids. Substances containing more than 15 carbon atoms are in a solid state.

What have we learned?

Substances with similar properties - alkanes and cycloalkanes - belong to saturated hydrocarbons. Alkanes are compounds with a linear molecular structure, cycloalkanes are cyclic hydrocarbons that form triangular, quadrangular, pentagonal structures. Saturated hydrocarbons are obtained from minerals, as well as industrially or in the laboratory. These are low-active substances that enter into substitution, addition, combustion, and decomposition reactions only under additional conditions.

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Hydrocarbons are the simplest organic compounds. They are made up of carbon and hydrogen. Compounds of these two elements are called saturated hydrocarbons or alkanes. Their composition is expressed by the formula CnH2n+2, common to alkanes, where n is the number of carbon atoms.

In contact with

Classmates

Alkanes - the international name for these compounds. These compounds are also called paraffins and saturated hydrocarbons. The bonds in alkanes molecules are simple (or single). The remaining valences are saturated with hydrogen atoms. All alkanes are saturated with hydrogen to the limit, its atoms are in a state of sp3 hybridization.

Homologous series of saturated hydrocarbons

The first in the homologous series of saturated hydrocarbons is methane. Its formula is CH4. The ending -an in the name of saturated hydrocarbons is a distinctive feature. Further, in accordance with the given formula, ethane - C2H6, propane - C3H8, butane - C4H10 are located in the homological series.

From the fifth alkane in the homologous series, the names of compounds are formed as follows: a Greek number indicating the number of hydrocarbon atoms in the molecule + the ending -an. So, in Greek the number 5 is pende, so after butane comes pentane - C5H12. Next is hexane C6H14. heptane - C7H16, octane - C8H18, nonane - C9H20, decane - C10H22, etc.

The physical properties of alkanes change noticeably in the homologous series: the melting and boiling points increase, and the density increases. Methane, ethane, propane, butane under normal conditions, i.e. at a temperature of approximately 22 degrees Celsius, are gases, pentane to hexadecane inclusive are liquids, and heptadecane are solids. Starting with butane, alkanes have isomers.

There are tables showing changes in the homologous series of alkanes, which clearly reflect their physical properties.

Nomenclature of saturated hydrocarbons, their derivatives

If a hydrogen atom is abstracted from a hydrocarbon molecule, monovalent particles are formed, which are called radicals (R). The name of the radical is given by the hydrocarbon from which this radical is produced, and the ending -an changes to the ending -yl. For example, from methane, when a hydrogen atom is removed, a methyl radical is formed, from ethane - ethyl, from propane - propyl, etc.

Radicals are also formed by inorganic compounds. For example, by removing the hydroxyl group OH from nitric acid, you can obtain a monovalent radical -NO2, which is called a nitro group.

When separated from a molecule alkane of two hydrogen atoms, divalent radicals are formed, the names of which are also formed from the names of the corresponding hydrocarbons, but the ending changes to:

• ylen, if the hydrogen atoms are removed from one carbon atom,
• ylene, in the case where two hydrogen atoms are torn from two adjacent carbon atoms.

Alkanes: chemical properties

Let's consider reactions characteristic of alkanes. All alkanes share common chemical properties. These substances are inactive.

All known reactions involving hydrocarbons are divided into two types:

• cleavage of the C-H bond (an example is a substitution reaction);
• rupture of the C-C bond (cracking, formation of separate parts).

Radicals are very active at the time of formation. By themselves they exist for a fraction of a second. Radicals easily react with each other. Their unpaired electrons form a new covalent bond. Example: CH3 + CH3 → C2H6

Radicals react easily with molecules of organic substances. They either attach to them or remove an atom with an unpaired electron from them, as a result of which new radicals appear, which, in turn, can react with other molecules. With such a chain reaction, macromolecules are obtained that stop growing only when the chain breaks (example: the combination of two radicals)

Free radical reactions explain many important chemical processes, such as:

• Explosions;
• Oxidation;
• Petroleum cracking;
• Polymerization of unsaturated compounds.

Details chemical properties can be considered saturated hydrocarbons using methane as an example. Above we have already considered the structure of an alkane molecule. The carbon atoms in the methane molecule are in a state of sp3 hybridization, and a fairly strong bond is formed. Methane is a gas with odor and color. It is lighter than air. Slightly soluble in water.

Alkanes can burn. Methane burns with a bluish pale flame. In this case, the result of the reaction will be carbon monoxide and water. When mixed with air, as well as in a mixture with oxygen, especially if the volume ratio is 1:2, these hydrocarbons form explosive mixtures, which makes it extremely dangerous for use in everyday life and in mines. If methane does not burn completely, soot is formed. In industry, this is how it is obtained.

Formaldehyde and methyl alcohol are obtained from methane by its oxidation in the presence of catalysts. If methane is heated strongly, it decomposes according to the formula CH4 → C + 2H2

Methane decay can be carried out to an intermediate product in specially equipped ovens. The intermediate product will be acetylene. The reaction formula is 2CH4 → C2H2 + 3H2. The separation of acetylene from methane reduces production costs by almost half.

Hydrogen is also produced from methane by converting methane with water vapor. Substitution reactions are characteristic of methane. Thus, at ordinary temperatures, in the light, halogens (Cl, Br) displace hydrogen from the methane molecule in stages. In this way, substances called halogen derivatives are formed. Chlorine atoms By replacing hydrogen atoms in a hydrocarbon molecule, they form a mixture of different compounds.

This mixture contains chloromethane (CH3 Cl or methyl chloride), dichloromethane (CH2Cl2 or methylene chloride), trichloromethane (CHCl3 or chloroform), carbon tetrachloride (CCl4 or carbon tetrachloride).

Any of these compounds can be isolated from the mixture. In production, chloroform and carbon tetrachloride are of great importance, due to the fact that they are solvents of organic compounds (fats, resins, rubber). Methane halogen derivatives are formed by a chain free radical mechanism.

Light affects chlorine molecules as a result they fall apart into inorganic radicals that abstract a hydrogen atom with one electron from the methane molecule. This produces HCl and methyl. Methyl reacts with a chlorine molecule, resulting in a halogen derivative and a chlorine radical. The chlorine radical then continues the chain reaction.

At ordinary temperatures, methane is sufficiently resistant to alkalis, acids, and many oxidizing agents. The exception is nitric acid. In reaction with it, nitromethane and water are formed.

Addition reactions are not typical for methane, since all valences in its molecule are saturated.

Reactions in which hydrocarbons participate can occur not only with the cleavage of the C-H bond, but also with the cleavage of the C-C bond. Such transformations occur in the presence of high temperatures and catalysts. These reactions include dehydrogenation and cracking.

From saturated hydrocarbons, acids are obtained by oxidation - acetic acid (from butane), fatty acids (from paraffin).

Methane production

Methane in nature distributed quite widely. It is the main component of most flammable natural and artificial gases. It is released from coal seams in mines, from the bottom of swamps. Natural gases (which is very noticeable in associated gases from oil fields) contain not only methane, but also other alkanes. The uses of these substances are varied. They are used as fuel in various industries, medicine and technology.

In laboratory conditions, this gas is released by heating a mixture of sodium acetate + sodium hydroxide, as well as by the reaction of aluminum carbide and water. Methane is also obtained from simple substances. For this, prerequisites are heating and catalyst. The production of methane by synthesis based on water vapor is of industrial importance.

Methane and its homologues can be obtained by calcination of salts of the corresponding organic acids with alkalis. Another method for producing alkanes is the Wurtz reaction, in which monohalogen derivatives are heated with sodium metal.