Fluorous Biphasic Catalytic Oxidation of Sulfides by Molecular Oxygen/2,2-Dimethylpropanal

The use of perfluoroalkyl-substituted cobalt complexes as catalysts for the oxidation of alkyl aryl sulfides with molecular oxygen/2,2-dimethypropanal has been studied in a fluorous organic biphasic system. The addition of very small amounts of a CoII−tetraarylporphyrin (Co-4) led to increased substrate conversions (67−100%). Sulfoxide was generally obtained as the main product, together with variable quantities of sulfone (0−100%), depending on the nature of the substrate. A perfluoroalkyl-substituted CoII−phthalocyanine (Co-6) proved to be less efficient with regard to substrate conversion (40−78%), but afforded sulfoxides selectively. Although the mechanism has not been investigated in detail, the reaction probably proceeds through a free-radical oxidative process, initiated by the CoII complexes. The attempts at recycling the catalysts through phase separation were partly ineffectual owing to their instability under the reaction conditions, which is more pronounced in the case of Co-6.