Manganeseporphyrin-catalysed heterogeneous and unusually chemioselective oxidations of sulfides by monopersulfate in supercritical CO2

The oxidation of sulfides by Oxone((R)) in the presence of catalytic amount of various manganese porphyrins in supercritical CO2 (scCO(2)) has been st udied. The reactions have been carried out in an anhydrous two phase-system (solid Oxone((R))) solid catalyst/scCO(2)). In the experimental conditions employed (40 degreesC, 20 MPa), only the new synthesised 5,10,15,20-tetrak is (heptafluoropropyl)porphyrinate manganese(III) chloride showed a slight solubility in scCO(2). In the absence of manganese porphyrin and/or of an a romatic nitrogen base a slow stoichiometric sulfide oxidation leading mainl y to sulfoxide is observed ((R)) in scCO(2). Conversely, in the presence of 4-tert-butylpyridine and catalytic in spite of the extremely low solubilit y of Oxone amount of manganese porphyrins (0.6% with respect to sulfide) en hanced reaction rates are observed. Furthermore, the selectivity of sulfide oxidation reverses and sulfone is formed in larger or comparable amount th an sulfoxide even when an excess of sulfide over oxidant is employed. The r esults collected suggest that the local concentration of the intermediate s ulfoxide around the catalyst is higher than that of the bulk supercritical phase thus determining unusual high reaction rates for sulfone formation. ( C) 2000 Elsevier Science B.V. All rights reserved.