The aniline catalysed decarboxylation of oxaloacetic acid

Abstract

Aniline catalysis of the decarboxylation of oxaloacetic acid, HO₂CCOCH₂CO₂H + CH₃COCO₂H + CO₂, has been studied in water and ethanol as solvent at 25°. In aqueous solution a maximum occurs in the pH-rate profile at pH 3.9, indicating the participation of a single proton in the transition state. Experiments with the half ester HO₂CCOCH₂CO₂Et, which does not decarboxylate in the presence of amines, suggest that in aqueous solution the intermediate in the reaction is a carbinolamine formed between the amine and the keto group of the acid, and not a Schiff's base as has been previously suggested. In ethanol solution the intermediate is a Schiff's base, and formation of the Schiff's base is the rate-determining step, the actual decarboxylation being a fast process.