Reactive oxygen species in aerobic decomposition of thiourea dioxides

Thiourea dioxides decompose in air-saturated alkaline solutions to give dit hionite, S2O42-. Kinetics of decomposition of aminoiminomethanesulfinic aci d (AIMSA), methylaminoiminomethanesulfinic acid (MAIMSA) and dimethylaminoi minomethanesulfinic acid (DMAIMSA) were studied in alkaline solutions under aerobic and anaerobic conditions. No dithionite was formed in strictly ana erobic conditions. Dithionite, however, was formed in the presence of KO2 a nd H2O2 under anaerobic conditions. The rate of decomposition was fastest f or DMAIMSA and slowest for MAIMSA. The proposed mechanism involves the init ial formation of the dioxosulfate(2-) ion, SO22-, through the heterolytic c leavage of the C-S bond. The dioxosulfate(2-) ion then reacts with dioxygen to give a series of reactive oxygen species: superoxide, peroxide and the hydroxyl radical. The expected dismutation of superoxide is important only in weakly alkaline solutions of pH less than 10. It is suggested, for the r st time, that the reactive oxygen species and the sulfur leaving groups may be responsible for the toxicity observed in most thioureas.