OXIDATION OF SULFIDES WITH ELECTROCATALYTIC P-450 MODEL SYSTEM

Controlled potential electrolysis (CPE) of meso-tetraphenylporphyrinat omanganese (III) chloride (1mM, 1a) at -0.4V (vs. saturated calomel el ectrode (SCE)) in acetonitrile containing diphenyl sulfide (100mM, 2), 1-methylimidazole (5 mM), and tetrabutylammonium perchlorate (0.1 M) as supporting electrolyte with a reticulated vitreous carbon (RVC) cat hode and bubbling O-2 gas, gave diphenylsulfoxide (12.6%-16.4%, 3) and diphenylsulfone (0.5%-1.5%, 4) in the presence of acetic acid/or tetr amethylammonium hydroxide (5). In the absence of acetic acid or 5, com pound 2 was not oxidized. The results of cyclic voltammetry and CPE at -0.4 V (vs. SCE) showed that the oxidant of 2 was an ore-manganese (V ) species which was generated from la and dissolved dioxygen by two-el ectron transfer and that the presence of H+ was essential not only to cleave the O-O bond in the peroxo-manganese species, but also to trans fer the second electron. This catalytic cycle is similar to that of P- 450. The current efficiency was 79.1%. CPE of dissolved O-2 was carrie d out at - 1.0 V in acetonitrile and superoxide ion was detected by us e of an electron spin resonance spectrometer in the frozen electrolyze d solution. Addition of potassium superoxide to acetonitrile containin g 1a, 1-methylimidazole and 2 gave 3 (15.6%-26.7%) and 4 (0%-2.7%) in the presence of acetic acid or 5. A similar procedure in the absence o f the acid or 5 did not give 3 or 4. When the applied potential was - 1.0 V, superoxide ion generated by cathodic reduction of dissolved oxy gen in the electrolytic solution containing acetic acid was converted into hydrogen peroxide by the reaction with protons. The reaction of m anganese (III) porphyrin with hydrogen peroxide produced an ore-mangan ese (V) species, which is a strong oxidant and oxidized 2 and 3. This mechanism is similar to the shunt mechanism in the cytochrome P-450 ca talytic cycle.