Mechanism of decomposition of sodium dithionite in aqueous solution

Abstract

The thermal decomposition of sodium dithionite in aqueous solution has been followed by means of e.p.r. signal intensity measurements. Two different reactions have been identified. The first one, catalyzed by bisulphite ion, proceeds according to the usual second-order autocatalytic reaction mechanism. The second one, much faster than the first one, appears after an induction period and ends as soon as a sufficient amount of decomposition product has been formed. Using previously reported values for the equilibrium constant for dithionite ion dissociation, values for the rate constant of the autocatalytic reaction are reported, and a mechanism for the decomposition is proposed.