Imidazole-based Vanadium Complexes as Haloperoxidase Models for Oxidation Reactions

Abstract

Four imidazole-bound oxovanadium(IV) haloperoxidase model complexes were prepared. Two heterogeneous catalysts were prepared by first linking imidazole-4-carboxylic acid or 1-methylimidazole-2-carboxylic acid to chloromethylated polystyrene and subsequently reacting these polymer anchored ligands with vanadyl sulphate. Two homogeneous catalysts were prepared by reaction vanadyl sulphate with the free ligands. The activity of the catalysts was evaluated for the hydrogen peroxide facilitated oxidation of styrene and ethylbenzene and thioanisole. A maximum conversion of 99.9 % for styrene and 10.6 % for ethylbenzene was achieved. Excellent conversions of thioanisole (100 %) were obtained under mild room temperature conditions. The heterogeneous catalysts also proved to be recyclable for this reaction, with no appreciable loss in activity even after three catalytic cycles. The haloperoxidase activity was evaluated spectrophotometrically by following the bromination of phenol red to bromophenol blue. All four catalysts proved effective in catalysing this process.

Keywords: Oxovanadium, Imidazole, Catalysis, Oxidation