Oxyhalogen−Sulfur Chemistry:  Nonlinear Oxidation Kinetics of Hydroxymethanesulfinic Acid by Acidic Iodate

The oxidation of hydroxymethanesulfinic acid, HMSA, by acidic iodate has been studied by spectrophotometric techniques. The reaction presents clock reaction characteristics in which in excess iodate conditions there is an initial quiescent period that is followed by a rapid production of iodine. The induction period before formation of iodine is inversely proportional to the iodate concentrations and the concentrations of acid to the second order. Iodide ions have a strong catalytic effect on the rate of the reaction by reducing the duration of the induction period. The stoichiometry of the reaction is dependent on the ratio of oxidant to reductant. In excess HMSA conditions the stoichiometry was deduced to be 3HOCH2SO2H + 2IO3- → 3HCHO + 3SO42- + 2I- + 6H+ whereas in excess iodate and after prolonged standing the stoichiometry is 6IO3- + 5HOCH2SO2H → 5SO42- + 5HCOOH + 3I2 + 4H+ + 3H2O. The mechanism is dominated by the standard oxyiodine kinetics that involve the initial formation of the reactive oxyiodi...