Direct Synthesis of Nitriles from Carboxylic Acids Using Indium-Catalyzed Transnitrilation: Mechanistic and Kinetic Study

Aliphatic and aromatic carboxylic acids can be quantitatively converted to the corresponding nitriles in the presence of catalysts using acetonitrile both as a solvent and reactant at 200 degrees C. This transformation is based on the acid-nitrile exchange (i.e., transnitrilation) and uses a nontoxic and water resistant catalyst, indium trichloride (InCl3). The mechanism of the transnitrilation was investigated both experimentally and computationally and compared to the previously proposed mechanism. In contrast to the usually assumed formation of amide as an intermediate, transnitrilation is an equilibrium reaction and proceeds via an equilibrated Mumm reaction with the formation of an imide as an intermediate. A simple and reversible mechanism was proposed for this reaction, which was validated by kinetics measurement and by density calculations of the functional theory reaction intermediates and reaction mechanisms.