Kolbe electrolysis

"Kolbe reaction" redirects here. For the carboxylation of phenols, see Kolbe–Schmitt reaction.

The Kolbe electrolysis or Kolbe reaction is an organic reaction named after Hermann Kolbe.^[1] The Kolbe reaction is formally a decarboxylative dimerisation of two carboxylic acids (or carboxylate ions). The overall reaction is:

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.^[2] 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:^[3]

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.^[4][5]

Applications

Kolbe electrolysis has a few industrial applications.^[6] In one example, sebacic acid has been produced commercially by Kolbe electrolysis of adipic acid.^[7]

Kolbe electrolysis has been examined for converting biomass into biodiesel^[8][9] and for grafting of carbon electrodes.^[10][11]

See also

• Electrosynthesis
• Wurtz reaction