Selective Oxidation of Alkylarenes with H2O2 Catalyzed by γ-Keggin Divanadium-substituted Polyoxometalate
The possibility of application of [γ-PW10V2O40] 5- polyoxometalate as catalyst for the selective oxidation of pseudocumene (PC) and 2-methylnaphthalene (2-MN) with H2O2 in MeCN/tBuOH solvent (1:1 v/v) in the presence of mineral acid was explored .The reaction mechanism was studied by experimental and theoretical methods. Unusually high chemo- and regioselectivity towards 2,3,5-trimethylphenol (TMP) was found in PC oxidation. Atypical regioselectivity was found in the oxidation of 2-MN where 6-methyl-1,4-naphthoquinone predominates over 2-methyl-1,4-naphthoquinone. DFT studies revealed that the formation of 2,3,5-TMP in PC oxidation is, most likely, due to peroxo complex [γ-PW10O38V2(O2)]3- (I), which may arise from dehydration of hydroperoxo complex [γ-PW10O38V2(OH)(OOH)]3- formed upon interaction of the H2[γ-PW10V2O40] 3- with Н2О2. The kinetic regularities and estimated rate constants acquired from the kinetic study on PC oxidation with H2O2 are in good agreement with the theoretically predicted reaction mechanism where I is the main active species responsible for the aromatic ring hydroxylation.