Formation and hydrolysis of acetals catalysed by acid Faujasites

Dimethyl and cyclic ethylene acetals can be obtained in the presence of HY zeolites by treatment of the corresponding carbonyl compound with trimethyl orthoformate at room temperature or with ethylene glycol using a Dean-Stark system, respectively. The relationship between the percentage of Na+ exchange of the zeolite and the initial reaction rates shows that only strong acid sites are active in the dimethyl acetal formation. Similarly, regeneration of the parent carbonyl compound was accomplished by simply heating suspensions of the appropriate acetal in carbon tetrachloride with HY catalysts. Evidence supporting the implication in the hydrolysis of the adsorbed water remaining on the zeolite after thermal activation was drawn from the results obtained using a dried solvent and a highly dealuminated zeolite. The possibility of using hydrolytic cleavage of acetals as a chemical activation procedure for zeolites was tested.