Ketonic decarboxylation

In organic chemistry, ketonic decarboxylation (also known as decarboxylative ketonization) is a type of organic reaction and a decarboxylation converting two equivalents of a carboxylic acid (R−C(=O)OH) to a symmetric ketone (R₂C=O) by the application of heat. It can be thought of as a decarboxylative Claisen condensation of two identical molecules. Water and carbon dioxide are byproducts:

2 RCO₂H → R₂CO + CO₂ + H₂O

Bases promote this reaction. The reaction mechanism likely involves nucleophilic attack of the alpha-carbon of one acid group on the other acid group's carbonyl (C=O), possibly as a concerted reaction with the decarboxylation. The initial formation of an intermediate carbanion via decarboxylation of one of the acid groups prior to the nucleophilic attack has been proposed, but is unlikely since the byproduct resulting from the carbanion's protonation by the acid has never been reported.^[1] This reaction is different from oxidative decarboxylation, which proceeds through a radical mechanism and is characterised by a different product distribution in isotopic labeling experiments with two different carboxylic acids. With two different carboxylic acids, the reaction behaves poorly because of poor selectivity except when one of the acids (for example, a small, volatile one) is used in large excess.