| Abstract
| - The kinetics and mechanisms of the oxidation of I− and Br− by trans-[RuVI(N2O2)(O)2]2+ have been investigated in aqueous solutions. The reactions have the following stoichiometry: trans-[RuVI(N2O2)(O)2]2+ + 3X− + 2H+ → trans-[RuIV(N2O2)(O)(OH2)]2+ + X3− (X = Br, I). In the oxidation of I− the I3−is produced in two distinct phases. The first phase produces 45% of I3− with the rate law d[I3−]/dt = (ka + kb[H+])[RuVI][I−]. The remaining I3− is produced in the second phase which is much slower, and it follows first-order kinetics but the rate constant is independent of [I−], [H+], and ionic strength. In the proposed mechanism the first phase involves formation of a charge-transfer complex between RuVI and I−, which then undergoes a parallel acid-catalyzed oxygen atom transfer to produce [RuIV(N2O2)(O)(OHI)]2+, and a one electron transfer to give [RuV(N2O2)(O)(OH)]2+ and I•. [RuV(N2O2)(O)(OH)]2+ is a stronger oxidant than [RuVI(N2O2)(O)2]2+ and will rapidly oxidize another I− to I•. In the second phase the [RuIV(N2O2)(O)(OHI)]2+ undergoes rate-limiting aquation to produce HOI which reacts rapidly with I− to produce I2. In the oxidation of Br− the rate law is −d[RuVI]/dt = {(ka2 + kb2[H+]) + (ka3 + kb3[H+]) [Br−]}[RuVI][Br−]. At 298.0 K and I = 0.1 M, ka2 = (2.03 ± 0.03) × 10−2 M−1 s−1, kb2 = (1.50 ± 0.07) × 10−1 M−2 s−1, ka3 = (7.22 ± 2.19) × 10−1 M−2 s−1 and kb3 = (4.85 ± 0.04) × 102 M−3 s−1. The proposed mechanism involves initial oxygen atom transfer from trans-[RuVI(N2O2)(O)2]2+ to Br− to give trans-[RuIV(N2O2)(O)(OBr)]+, which then undergoes parallel aquation and oxidation of Br−, and both reactions are acid-catalyzed.
- The kinetics and mechanisms of the oxidation of I− and Br− by trans-[RuVI(N2O2)(O)2]2+ have been investigated in aqueous solutions. In the oxidation of I−, parallel pathways involving both electron transfer and oxygen atom transfer are proposed. On the other hand, in the oxidation of Br−, oxygen atom transfer appears to be the only pathway.
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