Kinetics and mechanisms of the oxidation of iodide and bromide in aqueous solutions by a trans-dioxoruthenium(VI) complex

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Author(s)

  • William W. Y. Lam
  • Wai-Lun Man
  • Yi-Ning Wang
  • Tai-Chu Lau

Detail(s)

Original languageEnglish
Pages (from-to)6771-6778
Journal / PublicationInorganic Chemistry
Volume47
Issue number15
Publication statusPublished - 4 Aug 2008

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(N 2O2)(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 + k b[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 Ru VI and I-, which then undergoes a parallel acid-catalyzed oxygen atom transfer to produce [RuIV(N2O 2)(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(N2O 2)(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 = {(k a2 + kb2[H+]) + (ka3 + A b3[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, k a3 = (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(N 2O2)(O)(OBr)]+, which then undergoes parallel aquation and oxidation of Br-, and both reactions are acid-catalyzed. © 2008 American Chemical Society.

Citation Format(s)

Kinetics and mechanisms of the oxidation of iodide and bromide in aqueous solutions by a trans-dioxoruthenium(VI) complex. / Lam, William W. Y.; Man, Wai-Lun; Wang, Yi-Ning; Lau, Tai-Chu.

In: Inorganic Chemistry, Vol. 47, No. 15, 04.08.2008, p. 6771-6778.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review