Effect of zirconium addition on vanadium-catalyzed toluene oxidation by H2O2 in CH3COOH

The effect of zirconium addition on vanadium-catalyzed toluene oxidation by hydrogen peroxide in acetic acid was studied. V-51 NMR, ESI-MS and DFT calculation were used to characterize the intermediate metal species formed in the reaction. Over high vanadium amount, the addition of Zr is beneficial for benzaldehyde generation and toluene conversion, and the ratio of (benzaldehyde + benzoic acid)/(benzyl alcohol + benzyl acetate) was enhanced. Dimer of vanadium may directly coordinate to zirconium to form soluble mixed zirconium-vanadium polymeric species, which inhibited the further aggregation of vanadium. The structures of these species were determined by ESI-MS and DFT calculation. The trinuclear complex (OH)(OAc)Zr(mu-O)(2)V(OH)(mu-O)(2)V(OH)(OAc) showed compatible activity to the best catalyst VO(OH)(2)(OAc) for benzyl peroxide dehydration. The rate-determining step of benzyl peroxide dehydration catalyzed by metal species was the abstraction of alpha-H of PhCH2OO ligand. (C) 2012 Published by Elsevier B.V.