Kolbe electrolysis

The Kolbe electrolysis or Kolbe reaction is an organic reaction named after Hermann Kolbe. The Kolbe reaction is formally a decarboxylative dimerisation of two carboxylic acids (or carboxylate ions). The overall reaction is:

File:Electrólisis de Kolbe.png

If a mixture of two different carboxylates are used, all combinations of them are generally seen as the organic product structures:

3 R₁COO⁻ + 3 R₂COO⁻ → R₁−R₁ + R₁−R₂ + R₂−R₂ + 6 CO₂ + 6 e⁻

The reaction mechanism involves a two-stage radical process: electrochemical decarboxylation gives a radical intermediate, which combine to form a covalent bond. As an example, electrolysis of acetic acid yields ethane and carbon dioxide:

CH₃COOH → CH₃COO⁻ → CH₃COO· → CH₃· + CO₂

2CH₃· → CH₃CH₃

Another example is the synthesis of 2,7-dimethyl-2,7-dinitrooctane from 4-methyl-4-nitrovaleric acid:

Kolbe electrolysis, synthesis of 2,7-Dimethyl-2,7-dinitrooctane

The Kolbe reaction has also been occasionally used in cross-coupling reactions.

In 2022, it was discovered that the Kolbe electrolysis is enhanced if an alternating square wave current is used instead of a direct current.

Applications

Kolbe electrolysis has a few industrial applications. In one example, sebacic acid has been produced commercially by Kolbe electrolysis of adipic acid.

Kolbe electrolysis has been examined for converting biomass into biodiesel and for grafting of carbon electrodes.

See also

• Electrosynthesis
• Wurtz reaction