Reactive oxygen species in the aerobic decomposition of sodium hydroxymethanesulfinate

Sodium hydroxymethanesulfinate, (HOCH2SO2Na, HMS) is relatively stable in aqueous alkaline environments, but rapidly decomposes in acidic medium to give a variety of products that include sulfur dioxide. A detailed kinetic and mechanistic study of the decomposition of HMS in slightly acidic medium has shown a process that produces dithionite, S2O2-4, which is preceded by an induction period which persists for as long as molecular oxygen is present in the reaction solution. The complete consumption of molecular oxygen is a prerequisite for the formation of S2O2-4. Among some of the intermediates detected in the decomposition of HMS is the sulfite radical, SO-3. Comparisons are made between the decomposition mechanisms of thiourea dioxide (aminoiminomethanesulfinic acid) and HMS.