Ultimate hydrocarbons, or paraffins, are those bio compounds in the molecules of which the carbon atoms are connected by a simple (single) bond, and all other units of valency are saturated with hydrogen atoms.
Alkanes: physical properties
The first representatives of the homological series of methane are gases, from 512 to 1532 - liquids, starting from 1634 - solids. With an increase in the number of carbon atoms in the alkane molecule, their melting and boiling points naturally increase.
The boiling point of branched chain 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, and higher methane homologues do not. Limit hydrocarbons are lighter than water and practically insoluble 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 low reactivity. They are inert, which is displayed in their name - paraffins. This is due to the fact that in the structure of their molecules, C and H atoms are interconnected 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, you need to spend a lot of energy. Basic chem. the properties of alkanes, that is, the reactions they enter, are nitration, halogenation, sulfonation, sulfochlorination, cracking reactions. Radical reactions of alkanes initiate radicals, UV or gamma radiation, peroxides, heating. In this regard, they are characterized by two types of reactions: hydrogen substitution with a carbon-hydrogen bond cleavage and a molecule cleavage with a C — C or C — H bond cleavage.
Alkanes: chemical properties. Radical halogenation reaction
This reaction is sometimes called metalepsia. 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 successively replace hydrogen atoms in alkane molecules.
Alkanes: chemical properties. Nitration reaction
The nitro group easily replaces hydrogen in the tertiary, heavier in the secondary and very heavy in the primary carbon atoms. Now, on an industrial scale, alkane nitration is carried out in the gas phase at 150-490 ° C with nitric oxide or nitric acid fumes.
Alkanes: chemical properties. Sulfochlorination Reaction
Marginal hydrocarbons are exposed to a mixture of sulfur dioxide and chlorine. Catalysts are most often peroxides or UV radiation. This reaction is used to produce synthetic detergents (detergents). Alkyl sulfochlorides act with 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 alkanes from alkanes, or unsaturated hydrocarbons.
The elimination of hydrogen from an alkane molecule, or dehydrogenation, in the presence of catalysts and upon heating (up to 460 ° C) allows one to obtain the necessary alkenes. Methods have been developed for the oxidation of alkanes at low temperatures in the presence of catalysts (magnesium salts). This allows you to directionally influence the course of the reaction and to obtain the necessary oxidation products in the process of chemical synthesis. For example, the oxidation of higher alkanes produces a variety of higher alcohols or higher fatty acids.
Alkane cleavage 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 high-calorie fuel both in everyday life and in industry.