No abstract

A mild process for the selective oxidation of sulfides is in great demand. Therefore, probing the mechanism underlying the biological oxidation of sulfides under ambient conditions may provide valuable insights for the development of such a reaction. Based on porphyrin models of P450 enzymes, evidence of two key intermediates, Int0 and Int1, in this reaction is provided. Spectroscopic studies indicated the formation of a hydroperoxide-iron(III) species (Int0) upon addition of H(2)O(2). This intermediate proved to be highly selective for sulfoxide production. By contrast, a defined porphyrin oxoiron(IV) cation radical (Int1) directly reacted with sulfoxides, leading selectively to the corresponding sulfones. Interestingly, the available sulfoxides reversibly act as a new axial ligand for Int0 forming a more active species Int0(SO). The amount of Int0 increased in the presence of alkyl, aryl, or aromatic sulfides, while Int1 formed in the absence of these sulfides. Thus, sulfoxides and sulfones would selectively form under conditions that favor the corresponding intermediates, which elucidate the biological oxidation pathway.

The catalytic oxidative desulfurization (ODS) of dibenzothiophene (DBT) in decahydronaphthalene (decalin) was performed using the oil-soluble oxidant cyclohexanone peroxide (CYHPO) with a molybdenum oxide (MoO3) catalyst supported on macroporous polyacrylic cationic exchange resin D113 of weak acid series. The influence of the reaction temperature, reaction time, the molar ratio of CYHPO/DBT, and catalyst reuse was investigated in detail. In the presence of the catalyst MoO3/D113, the conversion of DBT to DBT sulfone was up to 100% at 100 °C in 40 min. The ODS was performed using other oil-soluble alkyl peroxides, i.e., tert-butyl hydroperoxide (TBHP) and tert-amyl hydroperoxide (TAHP), in comparison with the oxidative activity of CYHPO. The results showed that the activity of alkyl peroxides decreases in the order CYHPO > TAHP > TBHP, reversing the order of the peroxy oxygen electronic density. The oxidation mechanism is then discussed.