Oxyhalogen-Sulfur Chemistry: The Bromate-(Amininoimino)methanesulfinic Acid Reaction in Acidic Medium

Article abstract of DOI:10.1021/j100053a032

The reaction between (amnoimino)methanesulfinic acid, HO2SC(NH)NH2(AIMSA), and bromate has been studied in acidic medium.In excess AIMSA the stoichiometry of the reaction is 2BrO3^- + 3AIMSA + 3H2O -> 3SO4^2- + 3CO(NH2)2 + 2Br^- + 6H⁺, and in excess bromate the stoichiometry is 4BrO3^- + 5AIMSA + 3H2O -> 5SO4^2- + 5CO(NH2)2 + 2Br2 + 6H⁺.Br2 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 SO4^2-, no SO4^2- formation is observed until Br2 production commences.The reaction is autocatalyzed by bromide.The reactive oxidizing species in solution are HOBr and Br2.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 = 2.5E-2M^-2s^-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.