Oxidation of Sulfur-Containing Compounds with HOF-CH₃CN

The HOF-CH₃CN complex, easily prepared by passing F₂ through aqueous acetonitrile, is an exceptionally efficient oxygen transfer agent. All types of sulfides have been oxidized to sulfones in excellent yields, in a few minutes at room temperature. The reaction proceeds through the formation of sulfoxides which at low temperatures of around -75°C could be isolated in good yields. It was demonstrated through a reaction with thianthrene 5-oxide (20) that HOF·CH₃CN is strongly electrophilic in nature. Sulfides with an electron-depleted sulfur atom such as perfluoroalkyl or aryl sulfides, which could not be well oxidized by any other method, were also efficiently converted to the corresponding sulfones in minutes. Thiophenes are generally hard to oxidize to the corresponding S-dioxides since the conditions required by the orthodox oxidants encourage consecutive typical ene and diene reactions. HOF·CH₃CN requires short reaction times and low temperatures, thus enabling the isolation of thiophene dioxides, some of which could not be made by any other way. It seems that apart from unprotected amines, other functional groups such as aromatic rings, ketones, hydroxyls, and ethers do not interfere, since the sulfur atom reacts considerably faster.