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

Several studies of the Mo(VI) and W(VI) catalyzed reaction of H2O2 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 H2O2 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, = k(cat)[MoO42-][I-] + K-uncat[H2O2][I-]with values of k(cat) = 3.87 M-1 s(-1) and k(uncat) of 9.5 x 10(-3) M-1 s(-1) (at 27.8 degrees C). The values of Delta H-not equal 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 Delta H-not equal was found to be 41.1 kJ mol(-1) (at 21.8 degrees C) for the same system catalyzed with tungstate rather than molybdate. (C) 1999 Elsevier Science S.A. All rights reserved.