The simplest compounds studied in organic chemistry courses are saturated hydrocarbons or paraffins, also called alkanes. Their qualitative composition is represented by atoms of only two elements: carbon and hydrogen. Molecules of compounds contain only one type of chemical bond - single, or simple. In our article, we will study the structure, as well as methods for obtaining and properties of alkanes.
Representatives of the series and their names
The first compound of the paraffin class is methane. Its molecular formula is CH4, it corresponds to the general formula of substances, which is as follows: C H2 +2. The first four alkanes have individual names, such as methane, ethane. Starting from the fifth compound, the nomenclature is built using Greek numerals. For example, a substance with five carbon atoms in the molecule C5H12 is called pentane (from the Greek word "penta" - five). According to the rational nomenclature, alkanes,the chemical properties and production of which we are studying can be represented in the form of substances - derivatives of methane. In its molecule, one or more hydrogen atoms are replaced by hydrocarbon radicals. According to the systematic nomenclature, you should choose the longest chain of carbon atoms, which are numbered from the end to which the radicals are closer. Then the number of the carbon atom linked by a sigma bond to the radical particle is determined, and the radical is refined by adding the name of the alkane itself to it, for example, 3-methylbutane.
Production of alkanes
The main and most common source of paraffin production are minerals: natural gas and oil. Traces of methane along with hydrogen and nitrogen can be found in swamp gas. Solid alkanes containing a large number of carbon atoms in the molecule are present in ozocerite. This is a mountain wax with a whole range of unique properties, the deposits of which are being developed, for example, in Western Ukraine. There are also a number of synthetic methods for the extraction of saturated hydrocarbons, in particular, by the reduction reaction. In industry, several methods can be distinguished for the production of alkanes using redox reactions, for example, between haloalkyls and hydrogen iodide or sodium amalgam. More simple is the reduction of alkenes, alkynes or alkadienes with hydrogen in the presence of a nickel catalyst. The reaction product will be the corresponding paraffin. The process can be expressed by the following equationreactions:
CH2 =CH2 + H2=H 3C-CH3 (ethane)
Alkaline melting of s alts of carboxylic acids
If you heat sodium s alt CH3COONa or other substances of this class, which include active metal atoms, with sodium hydroxide or soda lime, you can get saturated hydrocarbons. The first type of reaction is more often used in the laboratory, the second is used to accurately analyze the structure of the carboxylic acid that is part of the s alt. This method of obtaining alkanes allows you to observe the splitting of the carbon chain of the reagent and the decrease in the number of carbon atoms in it.
Wurtz reaction
Substances that are derivatives of paraffins, in which hydrogen atoms have been replaced by particles of chlorine, bromine or iodine, can interact with finely dispersed metallic sodium. The general reaction equation will be:
2RHal + 2Na → R-R + 2NaHal, This process was discovered in 1870 by the French chemist F. Wurz. Later, P. P. Sharygin clarified its mechanism leading to the production of an alkane. It turned out that the halogen atom is first replaced by a metal. Then the resulting organosodium substance interacts with another haloalkane molecule. This reaction has found application in the technology of synthesis of higher paraffins.
Properties of saturated hydrocarbons
The physical characteristic of each class of organic compounds is determinedproperties that change naturally and depend on the structure of the molecules of substances. So, the first four homologues of alkanes, the reactions of which we considered earlier, are gases. Paraffins containing in their composition from 5 to 14 carbon atoms exist in the liquid phase, while the remaining alkanes are solid compounds. Gaseous and solid substances are odorless, liquid paraffins smell like kerosene or gasoline. The most important chemical properties of substances include, for example, hard oxidation - combustion, as a result of which a large amount of heat is released:
CH4 + 2O2=CO2 + 2H 2O
Recall that methane is the main component of the main fuel - natural gas.
Substitution reactions
Halogenation, which takes place according to the free radical mechanism, is another feature of alkanes. It refers to substitution reactions and leads to the formation of compounds - halogen derivatives of paraffins:
C5H12+Cl2=HCl + C5 H11Cl (chloropentane).
Nitration is the interaction of alkanes with dilute nitrate acid in the presence of a catalyst and under pressure, discovered in 1889 by N. M. Konovalov. Paraffin nitro compounds have a wide range of applications as raw materials for the production of rocket fuel, explosives, and for the extraction of carboxylic acids and amines.
Oxidation of higher members of the homologous series of alkanes in the presence of a catalyst leads to the production of alcohols and carboxylicacids used to synthesize plasticizers used in the manufacture of plastics and detergents.
In our article, we examined the properties of saturated hydrocarbons and studied how to obtain them.
