Catalytic isosafrol oxidation mediated by impregnated and encapsulated vanadyl-Y-zeolite under microwave irradiation

The paper reports the characterization of vanadyl-Y-zeolites produced via impregnation and encapsulation methods. Their catalytic activities for isosafrol oxidation, promoted via microwave irradiation, were evaluated in contrast of well-known catalysts, as V 2O 5/Y-zeolite composites and non-exchanged zeolite. ▪ Piperonal is an important intermediate in the synthesis of drugs like l-DOPA. Vanadyl-Y-zeolites have been tested as potential catalysts for this process. The use of encapsulated vanadyl compounds in Y-zeolite pores led to excellent rates of isosafrol oxidation under microwave irradiation. Native Y-zeolite better allowed the diffusion of the oxidant agent (hydrogen peroxide) through the catalyst pores compared to the VO-exchanged catalysts. This led to piperonal, which was also obtained due to the presence of V 5+ supported on one of the catalysts. These factors aided the extension of the oxidation process of isosafrol. On the other hand, vanadyl-zeolites, containing V 4+ species, promoted the reaction to intermediate (epoxide) with high selectivity under microwave radiation. Finally the impregnation of VO(Salen) on Y-zeolite showed better selectivity for epoxide formation than did the incorporated VO(Salen)-zeolite. Catalyst's surface area and availability of the vanadyl group were the main factors which allowed this superior performance.