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 (AIMSA), and bromate has been studied in acidic medium. In excess AIMSA the stoichiometry of the reaction is 2BrO(3)- + 3AIMSA + 3H(2)O --> SO42- + 3CO(NH2)2 + 2Br(-) + 6H(+), and in excess bromate the stoichiometry 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 excess over AIMSA. It is produced from the reaction of the product, Br-, with excess BrO3- after all the AIMSA has been consumed. The reaction has an initial induction period followed by formation of bromine. Although AIMSA is oxidized to SO42-, no SO42- formation is observed until Brz production commences. The reaction is autocatalyzed by bromide. The reactive oxidizing species in solution are HOBr and Br-2. Bromide enhances their formation from bromate. A simple eight-reaction mechanism is used to describe the reaction. The reaction commences through a direct reaction between BrO3- and AIMSA: BrO3- + HO2SC(NH)NH2 + H+ --> HBrO2 + HO3SC(NH)NH2 with k = 2.5 x 10(-2) M(-2) s(-1). The rate-determining step is the standard BrO3- Br- reaction which forms the reactive species HOBr: BrO3- + Br- + 2H(+) --> HBrO2 + HOBr. A computer simulation analysis of the proposed mechanism gave good fit to the data.