Reaction pathways for Zn(II)-catalyzed carboxylic acid esters hydrolysis

Reaction pathways have been investigated by quantum-mechanical procedures on gas phase models for the hydrolysis of methyl acetate catalyzed by a monohydroxo-Zn(II) complex formed by a phenanthroline-containing polyamine macrocycle. Based on consideration of energy barrier heights, the hydrolysis process is predicted to be bimolecular, consistently with kinetic data obtained for the hydrolysis of p-nitrophenyl acetate promoted by the modelled catalyst. Differences with respect to results of theoretical studies on the more extensively investigated hydrolysis processes catalyzed by the OH− anion are discussed and appear to be mostly due to the presence of the metal centre close to the OH function in the system now investigated. The pervasive presence and path-controlling role of hydrogen bonds are also discussed.