Tetrabutylammonium Chlorite as an Efficient Oxidant for Controlled Oxidation of Sulfides to Sulfoxides

Considering the demand for organosulfur materials and the challenges associated with currently used oxidation processes, in this study, we evaluated the counter-cation of sodium chlorite (Na⁺ClO₂ ^-) with tetrabutylammonium chloride (Bu₄N⁺Cl^-) to synthesise tetrabutylammonium chlorite (Bu₄N⁺ClO₂ ^-). Bu₄N⁺ClO₂ ^- exhibited good solubility in organic solvents like chloroform (5.2 mol L^-1) and ethyl acetate (2.8 mol L^-1). The oxygenation reaction of organosulfides with Bu₄N⁺ClO₂ ^- was examined in an HCl-acidic ethyl acetate solution under ambient conditions, selectively forming the corresponding sulfoxides as mono-oxygenated products. The reaction was initiated by the formation of chlorine dioxide (ClO₂⋅) as an oxidant and an active species generated from Bu₄N⁺ClO₂ ^- with HCl. This oxygenation method also enables the surface oxidation of sulfide polymers like polyphenylene sulfide (PPS) resins to increase their surface hydrophilicity. Therefore, the use of Bu₄N⁺ClO₂ ^- for applications in organic solvents is an efficient, and highly selective approach for selective oxidation.