Short time biomimetic oxidation of styrene with aqueous hydrogen peroxide: Crucial roles played by acetic acid

Very low catalytic activity and high degrees of oxidative degradation of manganese porphyrins can be overcome by conducting the oxidation of olefins in the presence of acetic acid. [Display omitted] Short time oxidation of styrene with aqueous hydrogen peroxide catalyzed by a series of manganese porphyrins, MnT(aryl)PP(OAc), (aryl = phenyl, 2-chlorophenyl, 2-methylphenyl, 4-chlorophenyl or 4-methoxyphenyl) was studied under different conditions. In contrast to most previous catalytic systems containing manganese porphyrins and terminal oxidants other than hydrogen peroxide, no oxidation products were observed in the presence of the manganese porphyrins and various amounts of a nitrogen donor co-catalyst. Also, the addition of small and large alcohols to the reaction mixture had no positive effect on the efficiency of the catalyst, although the oxidative stability of the catalyst increased in the case of methanol. The oxidative stability and catalytic activity of the catalysts were remarkably increased in the presence of acetic acid. Furthermore, conducting the oxidation reaction in the presence of acetic acid and an optimized amount of imidazole decreased the reaction time from 120 to 20 min. However, the addition of bicarbonate had no effect on the catalytic performance of the catalysts. A mechanism was proposed to explain the crucial roles played by acetic acid in this catalytic system, using competitive epoxidation of cis-and trans-stilbene to elucidate the active oxidant species involved in the catalytic cycle of the oxidation reaction.