Oxygenation of Organic Sulfides Catalyzed by Simple Fe(III) Salts

Interest in the oxidation of organic sulfides originates from the need to remove sulfur compounds from fossil fuels and for the detoxification of V type agents and muster gas. Moreover, sulfoxides are important intermediates in the synthesis of natural products and biologically significant molecules. Additionally, sulfoxide functional group is often the key component in common medicines. For instance, omeprazole, one of the world’s highest selling drugs (marketed as Losec / Prilosec by AstraZeneca), contains a central S=O group that is key to the inhibition of the gastric acid production. Key to the synthesis of the above-mentioned compounds is the chemical selectivity in converting an organic sulfide to the corresponding sulfoxide without the formation of over-oxidized byproduct sulfone. Organic sulfide oxygenation by hydrogen peroxide (H₂O₂) was effectively accomplished at room temperature in the presence of catalytic amounts of simple iron(III) salts. The effect of different solvents on the rate of conversion was also examined and the system showed good reactivity toward sulfide oxidation in all solvents studied.  The iron salts used in this study were able to convert the sulfides to the sulfoxide in acetonitrile with yields between 46-91%.  Using acetone, ethanol, and methanol yields between 26-92% of the sulfoxide were obtained. The reaction can also take place under organic-aqueous biphasic conditions affording 100% of the sulfoxide.  In summary, our method is very efficient, safe, inexpensive and high yielding but more importantly a catalytic process was developed were a 100% chemical selectivity for sulfoxide was achieved.