General acid catalysis in benzoic acid-Crystal Violet carbinol base reactions in toluene

Abstract

Kinetics of benzoic acid-dye carbinol base reactions in an apolar aprotic solvent exhibit a complex dependence on the concentration of the acid, indicating the occurrence of general acid catalysis, the acid playing the dual role of the substrate and the catalyst. The complex kinetic behavior observed for 23 ortho- and meta-substituted benzoic acids has been traced to overlapping participations of the monomer acid, hyperacidic open chain homoconjugated complex (dimeric and trimeric) acids, and nonreactive cyclic dimer and trimer acids. It has been found that although the degree of proton transfer in the transition state is 50-60% when the acid acts exclusively in the monomeric form, it gets enhanced to as high as more than 90% when the role of homoconjugated complex acids is taken into consideration. © 2012 Wiley Periodicals, Inc.