Solvent-free selective oxidation of CH bonds of toluene and substituted toluene to aldehydes by vanadium-substituted polyoxometalate catalyst

A novel homogeneous vanadium-substituted polyoxometalate catalyst of [n-Bu4N]3H3[PW9V3O40] showed good catalytic activity for the activation of CH bonds of toluene and substituted toluene with TBHP (70% aq) under solvent-free conditions. Under the optimal conditions, a 65% yield of benzaldehyde and a TON of 5221 were obtained over this catalyst at 343 K. This catalyst also showed good conversion and selectivity for the oxidation of a series of substituted toluene. The vanadium-substituted Keggin-POM was not decomposed to some species upon the treatment of 530-fold of TBHP by IR characterization. A free radical mechanism was proposed based on the experimental results and the literature supports.

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► A homogeneous vanadium-substituted polyoxometalate catalyst was prepared.
► This catalyst showed good activity for oxidation of toluene and substituted toluene.
► A free radical mechanism was proposed based on the experimental results.