Reaction of organic sulfur compounds with superoxide anion—III : Oxidation of organic sulfur compounds to sulf1nic and sulfonic acids

Organic sulfur compounds such as disulfide, thiolsulfinate, thiolsulfonate, thiol, sodium thiolate, and sodium sultinale were readily oxidized to both sulfinic and sulfonic acids with superoxide anion generated from potassium superoxide and 18-crown-6-ether under mild conditions. However, both sulfide and sulfoxide did not react with superoxide anion, O₂^-. Although thiol was easily oxidized to disulfide with O₂^? at room temperature, it was oxidized further with O₂^? at 60° to the corresponding sulfinic and sulfonic acids. Symmetrical disulfide was obtained in the reaction of unsymmetrical thiolsulfinate or thiolsulfonate along with both sulfinic and sulfonic acids. Most reactive was thiolsulfinate which reacted at lower temperature ranging between ?40 and 0° to afford the products within 30 min. Relative reactivities fall in the following order: thiolsulfinate > thiolsulfonate > disulfide ? sodium thiolate ? sodium sulfinate. Polar solvents such as pyridine and acetonitrile were more effective than such a less polar solvent as benzene in the oxidation of the substrate, and increased amount of the crown ether shortened the reaction time. Nucleophilic attack of O₂^? and electron transfer processes are believed to be involved in these oxidations.