Alkanes: chemical properties

The limiting hydrocarbons, or paraffins, are those biocompounds in which the carbon atoms are connected by a simple (single) bond, and all other units of valence are saturated with hydrogen atoms.

Alkanes: physical properties

The first representatives of the homologous series of methane are gases, from C5H12 to C15H32 - liquids, starting with C16H34 - solids. With the increase in the number of carbon atoms in the alkane molecule, the points of their melting and boiling naturally increase.

The boiling point of branched hydrocarbons is much lower than the boiling point of their isomers. Methane and ethane are odorless, volatile liquid hydrocarbons have the smell of gasoline (pentane and hexane) and kerosene, the higher homologues of methane do not. The limiting hydrocarbons are lighter than water and practically do not dissolve in it. Saturated hydrocarbons are highly soluble in organic solvents, and liquid alkanes themselves are excellent solvents.

Alkanes: chemical properties

These bio-compounds are characterized by a low reactivity. They are inert, what is displayed in their name - paraffins. This is explained by the fact that in the structure of their molecules the atoms C and H are linked together by sigma bonds. The chemical inertness of these substances is due to the structural features of their molecules. In order to break the sigma-connection, it is necessary to spend a lot of energy. Basic chemical. Properties of alkanes, that is, the reactions to which they enter, are reactions of nitration, halogenation, sulfonation, sulfochlorination, cracking. Radical reactions of alkanes initiate radicals, UV or gamma radiation, peroxides, heating. In this regard, they are characterized by two types of reactions: the replacement of hydrogen with a break in the "carbon-hydrogen" bond and the cleavage of the molecule with the disruption of the C-C or С-Н bonds.

Alkanes: chemical properties. The radical halogenation reaction

This reaction is sometimes called metaleptic. It can be initiated by sunlight. In the dark at 250-400 ° C or in the presence of catalysts (copper chloride, tin chloride ), halogen atoms consistently replace hydrogen atoms in alkane molecules.

Alkanes: chemical properties. Reaction of nitration

The nitro group easily replaces hydrogen in the tertiary, heavier in the secondary and very hard in the primary carbon atoms. Now, on an industrial scale, nitriding of alkanes is carried out in the gas phase at 150-490 ° C with nitric oxide or nitrate acid vapor.

Alkanes: chemical properties. Sulfochlorination reaction

The limiting hydrocarbons are affected by a mixture of sulfur dioxide and chlorine. Catalysts are most often peroxides or UV radiation. This reaction is used to prepare synthetic detergents (detergents). Alkylsulfochlorides act on alkalis, which leads to the formation of alkaline salts of sulfonic acids, structural components of detergents (pastes, powders).

Saturated hydrocarbons are raw materials for the synthesis of a variety of organic substances. A prerequisite for the synthesis of many of them is the production of alkenes or unsaturated hydrocarbons from alkanes .

Cleavage of hydrogen from an alkane molecule, or dehydrogenation, in the presence of catalysts and with heating (up to 460 ° C) makes it possible to obtain the necessary alkenes. Methods for the oxidation of alkanes at low temperatures in the presence of catalysts (magnesium salts) have been developed. This makes it possible to influence the course of the reaction in a direct way and to obtain the necessary oxidation products in the course of chemical synthesis. For example, the oxidation of higher alkanes produces a variety of higher alcohols or higher fatty acids.

The cleavage of alkanes also occurs in other conditions (combustion, cracking). Saturated hydrocarbons burn with a blue flame with the release of a huge amount of heat. These properties make it possible to use them as a high-calorie fuel both in everyday life and in industry.