Oxovanadium(IV) Schiff base complexes encapsulated in zeolite-Y as catalysts for the liquid-phase hydroxylation of phenol

Liquid-phase hydroxylation of phenol with H2O2 to a mixture of catechol and hydroquinone in acetonitrile has been reported using oxovanadium(IV) Schiff base complexes encapsulated in zeolite-Y as catalysts. Reaction conditions have been optimized by considering the concentration of substrate and oxidant, amount of catalyst, volume of solvent and temperature. Under the optimized reaction conditions, [VO(sal-1,3-pn)]-Y (H(2)sal-1,3-pn = N,N'-bis(salicylidene)propane-1,3-diamine) has shown the highest conversion of 34.3% after 6 h, [VO(salen)]-Y (H(2)salen = N,N'-bis(salicylidene)ethane-1,2-diamine) and [VO(saldien)]-Y (H(2)saldien = N,N'-bis( salicylidene)- diethylenetriamine) have comparable catalytic activity (similar to33% conversion) while [VO(sal-1,2-pn)]-Y (H(2)sal-1,2-pn = N,N'-bis(salicylidene)propane-1,2-diamine) has the poorest performance (10.6% conversion). All these catalysts are more selective (90%) toward catechol formation except [VO(sal-1,3-pn)]-Y, which only gives similar to68% selectivity.