ONE-POT SELECTIVE SYNTHESIS OF ETHYL-ESTERS FROM AROMATIC NITRILES USING ACID FAUJASITES AS CATALYSTS

In order to determine the potential of acidic zeolites as catalysts in the preparation of carboxylic esters from nitriles, faujasites, beta, and mordenite have been studied in a liquid ethanolic medium. From the results obtained, it can be concluded that the optimum zeolite for this reaction is the less acidic faujasite (Si/Al = 2.5). Competitive dehydration of ethanol takes place and, consequently, the two nucleophiles ethanol and water react with the nitrites. Zeolites with the strongest acid sites (beta, mordenite) show higher activity in a first step of the process, particularly towards amide formation. A linear relationship between activity and acidity is established in this step for a competitive attack of the nucleophiles. After the strong acid sites have been poisoned by the product, the reaction is performed over the remaining less acidic free sites. A consecutive reaction takes place leading to the ester with good selectivities (80%) over faujasites. The probable operating mechanism involves as the first step a fast protonation of the nitrile, the rate-determining step being, as in homogeneous conditions, the nucleophilic attack. © 1993 Academic Press, Inc.