Study of the hydrolysis of acetonitrile using different Bronsted acid models: Zeolite-type and HCl(H2O)(x) clusters

The hydrolysis of acetonitrile has been studied theoretically by different ab initio methods (RHF, DFT, and MP2). Two Bronsted acid catalysts have bee n compared: zeolite and HCl(H2O) = (2,t) clusters. Some interesting analogi es have been found for the reaction path catalyzed by these different acids , especially in the hydration transition state. The size and the configurat ion of a zeolite cluster model have an important influence on predicting th e reaction mechanism. The van der Waals interactions also play an important role in this reaction. Due to these interactions, oxygen atoms of the zeol ite cavity can stabilize charged species as N- and O-protonated acetamide c onfigurations. For the zeolite catalyst, the rate-limiting step of the over all reaction is the hydration of acetonitrile. On the other hand, in the hy drochloric acid catalysis, the rate-limiting step is either the hydration o r the isomerization step. Acetamide appears to be the most stable species a dsorbed on zeolite and it is responsible for poisoning the reaction. (C) 20 00 Academic Press.