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. 51V 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(μ-O)2V(OH)(μ-O)2V(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 α-H of PhCH2OO ligand.

Vanadium–zirconium mixed soluble trimeric species could form after the addition of Zr in vanadium-catalyzed toluene oxidation system. The formed trimeric species (OH)(OAc)Zr(μ-O)2V(OH)(μ-O)2V(OH)(OAc) could effectively catalyze the dehydration of benzyl peroxide to form benzaldehyde.Figure optionsDownload high-quality image (104 K)Download as PowerPoint slideHighlights
► The formation of mixed soluble zirconium–vanadium species was reported.
► The formation of benzaldehyde was favored over that of benzyl alcohol by Zr addition.
► The structure of soluble Zr species was determined.
► Trinuclear Zr–V–V complex exhibits high activity on the dehydration of benzyl peroxide.