Sodium metavanadate catalyzed direct hydroxylation of benzene to phenol with hydrogen peroxide in acetonitrile medium

The homogenous liquid-phase direct catalytic oxidation of benzene to phenol was performed at room temperature in acetonitrile solvent using sodium metavanadate as the catalyst and hydrogen peroxide as the oxidant. The effects of various reaction parameters, such as acidity of the system, reaction temperature, reaction time and the amount of hydrogen peroxide used, were studied. Under the optimized conditions, a phenol yield of 13.5% with a selectivity of 94% was obtained. The variation of vanadium species during the reaction was studied by in situ 51V-NMR method. It was found that vanadium species existed as VO2+ before the reaction. In the presence of hydrogen peroxide, VO2+ species might be transferred to peroxovanadate species, such as HVO(O2)2, VO(O2)+, which oxidized benzene to phenol exerting the catalytic performance. A catalytic cycle involving the above mechanism was proposed.

Graphical abstractSodium metavanadate catalyzed direct hydroxylation of benzene to phenol with hydrogen peroxide in acetonitrile medium was studied. A satisfactory yield of 13.5% with a selectivity of 94% was obtained. A free radical mechanism involving the state variation of vanadium species was proposed based on in situ 51V-NMR. Figure optionsDownload full-size imageDownload as PowerPoint slide