Ketonic decarboxylation (also known as ketonization) is a type of organic reaction and a decarboxylation converting two equivalents of a carboxylic acid to a symmetric ketone by the application of heat with expulsion of one equivalent of water and one equivalent of carbon dioxide. Bases promote this reaction. The reaction mechanism likely involves formation of an intermediate carbanion with decarboxylation from one acid group followed by nucleophilic attack on the other acid group as a concerted reaction. This reaction is different from oxidative decarboxylation with 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 (small, volatile) is used in large excess. An example of intramolecular ketonization is the conversion of adipic acid to cyclopentanone with barium hydroxide. Of commercial importance is the production of 3-pentanone from propionic acid with catalysts cerium(IV) oxide and manganese dioxide on alumina.
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