OXYHALOGEN-SULFUR CHEMISTRY - OXIDATION OF HYDROXYMETHANESULFINIC ACID BY BROMATE IN AN ACIDIC MEDIUM

The reaction between hydroxymethanesulfinic acid, HOCH2SO2H (HMSA), an d bromate ion has been studied in the pH range 0.3-2.0. The stoichiome try of the reaction in excess HMSA was determined as BrO3- + HOCH2SO2H --> Br + SO42- + HCOOH + 2H(+). In excess bromate the stoichiometry i s 6BrO(3)(-) + 5HOCH(2)SO(2)H --> 3Br(2) + 5SO(4)(2-) + 5HCOOH + 4H(+) + 3H(2)O. In excess bromate, the reaction exhibits clock reaction beh avior. An initial induction period in which there is no redox potentia l or absorbance (lambda = 390 nm) activity is followed by a sudden and rapid production of B-r2. This is explained via the coupling of three reactions: oxidation of HMSA, production of Bra, and consumption of B -r2. The consumption of B-r2 is so fast that the end of the induction period is an indicator that all the HMSA has been consumed. The rapid B-r2-HMSA reaction also precludes oligooscillatory behavior, which see ms to de a usual feature of reactions between sulfur compounds and oxy halogen ions.