Kinetics of the molybdate and tungstate catalyzed oxidation of iodide by hydrogen peroxide

Abstract

Several studies of the Mo(VI) and W(VI) catalyzed reaction of H 2O 2 with various substrates have been documented previously. The experiments described herein attempt to settle some apparent contradictions in these reports. Specifically, the oxidation of I − with H 2O 2 in the presence of molybdate or tungstate ion in an acid solution was studied. The rate law for this system was found to be rate i= k cat[MoO 4 2−][I −]+ k uncat[H 2O 2][I −] with values of k cat=3.87 M −1 s −1 and k uncat of 9.5×10 −3 M −1 s −1 (at 22.8°C). The values of Δ H ≠ for the molybdate catalyzed and uncatalyzed reactions were found to be 39.4 and 56.8 kJ mol −1, respectively. Similarly, the value of k cat was found to be 32.7 M −1 s −1 and Δ H ≠ was found to be 41.1 kJ mol −1 (at 21.8°C) for the same system catalyzed with tungstate rather than molybdate.