A systematic study of the ancillary effect of different molecules on the acetonitrile hydrolysis

Transition states for the acetonitrile hydrolysis reaction (including hydration and isomerization steps) catalyzed by different proton donors have been studied by different quantum chemical methods (RHF, DFT and MP2), using different cluster models. HCl(H2O), HCl(H2O)(2), (H2O)(3), HCl(H2O)(3) and H3O+(H2O)(2) clusters were used for the hydration transition state and H2O, HCl, HCl(H2O) and H3O+ for the tautomerism (intramolecular proton migration) transition state. All ab initio methods showed complete qualitative agreement in the hydration transition stare geometry. In the tautomerization case, inclusion of electron correlation was required to obtain the correct transition stats geometry. The calculated activation barrier energies changed considerably for the different clusters. An ancillary effect of water and HCl was observed. In complementary studies, the effect of polar environment on HCl dissociation was analyzed via embedding calculations and by using HCl(H2O)(5) cluster. Although HCl dissociates in H2O, it was found not to protonate acetonitrile. (C) 2000 Elsevier Science B.V. All rights reserved.