Disulfide Oxidation in Water: Thiosulfinate Intermediates Dictate Redox Fate.

Disulfides (RSSR) are ubiquitous sulfur-containing compounds released from industrial additives, tire wear particles, and biological systems, yet their environmental transformation in aquatic matrices remains poorly understood. Once released into aquatic systems, RSSR contribute to odor episodes, impose high oxidant demand, and generate sulfur-related byproducts during treatment. Here, we elucidate the oxidative transformation network of RSSR through the formation and controlled reactivity of thiosulfinates (RS(O)SR) as key intermediates. Kinetic and computational analyses identify RS(O)SR as a pivotal branching point that undergoes competing oxidation, hydrolysis, and reduction reactions. Direct stepwise sulfur oxidation is kinetically unfavorable, whereas hydrolysis of RS(O)SR circumvents these barriers and is further promoted by OH or intramolecular -NH-assisted cyclization, enabling either regeneration of reduced sulfur species or complete oxidation to terminal sulfonic acids with diminished toxicity and odor potential. The resulting structure-reactivity framework quantitatively links electronic properties to oxidant specificity across diverse water-treatment oxidants. Overall, this study provides mechanistic insight into sulfur-centered redox cycling and offers guidance for controlling sulfurous pollutants, minimizing odor formation, and reducing problematic sulfur byproducts.