Question

Explain Kolbe’s electrolysis method.

Answer 1

Hint: Kolbe’s electrolysis method is a general method of preparation of substituted hydrocarbons from the substituted carboxylic acids by the use of the electric discharge method where carbon dioxide gas is released. It is one of the most widely used methods for the preparation of alkanes and substituted hydrocarbons.

Complete step by step answer:
The Kolbe’s electrolysis is an organic reaction that is named after the renowned scientist H. Kolbe. The Kolbe reaction is formally a decarboxylative dimerisation of two carboxylic acids or simply carboxylate ions. The term decarboxylative dimerisation means there is a loss of molecules of carbon dioxide and the alkyl groups join together directly. The reaction takes place in the presence of an electric discharge where the electrons play a key role. The overall reaction can be explained as:
$2RCO{O^ - }N{a^ + }\xrightarrow{{2{e^ - }}}R - R + 2C{O_2}$
As we can observe from the reaction mechanism, we find that the carboxylate compound loses carbon dioxide from it in the presence of electrons in the solution. The alphabet $R$ can be any alkyl, aryl or acyl group. The overall reaction takes place in two step radical process which includes:
(i) Electrochemical decarboxylation that gives a radical intermediate which is unstable and highly reactive in nature.
$R - COOH \to RCO{O^ - } \to R \bullet + C{O_2}$
(ii) Radical recombination: The radicals being chemically active recombine with each other with the help of a covalent bond to form a $R - R$ compound.
$R \bullet + \bullet R \to R - R$

Note:
Kolbe’s electrolysis is used in the mass production of symmetric alkanes in the chemical laboratories and industries. The electrochemical oxidative decarboxylation of carboxylic acid salts that leads to radicals, which dimerize. It is best applied to the synthesis of symmetrical dimers, but in some cases can be used with a mixture of two carboxylic acids to furnish unsymmetrical dimers.