Kolbe electrolysis

The Kolbe electrolysis is a chemical reaction, werden.Benannt when coupled by electrolysis of carboxylic acids or their salts, carboxylates, two radicals together was the Kolbe electrolysis after its discoverer Hermann Kolbe (1818-1884), of this reaction for the first time in 1849 published. He set up this way, for example ethane from acetic acid is:

Reaction mechanism

The salt of the carboxylic acid ( carboxyl anion ) is oxidized at the anode to the carboxylate radical. This radical reacts further with the elimination of carbon dioxide. In each case two radicals combine ( dimerized ) then to the alkane:

At the cathode, hydrogen is formed at the same time:

When DC voltage is applied, hiking the positively charged metal cations to the cathode ( the negative pole) and the negatively charged carboxylates to the anode where they react. As counter-ions for carboxylate alkali metal or alkylammonium cations are mostly used, as they have no influence on the reaction. Other metal ions such as Fe2 , Mn2 and Co2 reduce the yield.

Yield

For symmetrical n-alkanes, a yield of up to 90% can be achieved, depending on parameters such as current density, solvents, salt concentration and temperature. If different carboxylates used (mixed Kolbe electrolysis ), also products having an odd number of carbon atoms are accessible. The yields decrease, however, as is mostly the product mixtures are formed. The anode material is platinum has proven.

The yields of the reaction depend on various factors such as the substrate, the specific conditions of electrolysis, the current density and on the solvents used. The reaction is usually carried out at moderate temperatures.