NONLINEAR DYNAMICS IN CHEMISTRY DERIVED FROM SULFUR CHEMISTRY .4. OXYHALOGEN-SULFUR CHEMISTRY - THE BROMATE-(AMINOIMINO)METHANESULFINIC ACID REACTION IN ACIDIC MEDIUM

The reaction between (aminoimino)methanesulfinic acid, HO2SC(NH)NH2 (A IMSA), and bromate has been studied in acidic medium. In excess AIMSA the stoichiometry of the reaction is 2BrO(3)- + 3AIMSA + 3H(2)O --> SO 42- + 3CO(NH2)2 + 2Br(-) + 6H(+), and in excess bromate the stoichiome try is 4BrO(3)- + 5AIMSA + 3H(2)O --> 5SO(4)(2-) + 5CO(NH2)(2) + 2Br(2 ) + 6H(+). Br-2 is produced only when BrO3- is in stoichiometric exces s over AIMSA. It is produced from the reaction of the product, Br-, wi th excess BrO3- after all the AIMSA has been consumed. The reaction ha s an initial induction period followed by formation of bromine. Althou gh AIMSA is oxidized to SO42-, no SO42- formation is observed until Br z production commences. The reaction is autocatalyzed by bromide. The reactive oxidizing species in solution are HOBr and Br-2. Bromide enha nces their formation from bromate. A simple eight-reaction mechanism i s used to describe the reaction. The reaction commences through a dire ct reaction between BrO3- and AIMSA: BrO3- + HO2SC(NH)NH2 + H+ --> HBr O2 + HO3SC(NH)NH2 with k = 2.5 x 10(-2) M(-2) s(-1). The rate-determin ing step is the standard BrO3- Br- reaction which forms the reactive s pecies HOBr: BrO3- + Br- + 2H(+) --> HBrO2 + HOBr. A computer simulati on analysis of the proposed mechanism gave good fit to the data.