Reduction Potentials of SO3-, SO5.-, And S4O6.3- Radicals in Aqueous Solution

Published

November 1, 1999

Author(s)

T N. Das, Robert E. Huie, Pedatsur Neta

Abstract

Reduction potentials of the SO-₃ -, SO₅ -, and S₄O₆^3- radicals in aqueous solutions are measured by pulse radiolysis at 294 K. These radicals are produced by reaction of OH or N₃ radicals with sulfite, peroxymonosulfate, and thiosulfate anions, respectively. The potentials for the couples SO₃ -/SO₃^2- and SO₅ - /SO₅^2- are determined from equilibrium constants with three reference couples of the phenoxyl/phenoxide type, i.e. those derived from phenol, 3-cresol, and tyrosine. The potential for PhO /PhO - was redetermined against ClO₂ /ClO₂- and confirms the published value. The potentials for the other two phenols are determined against PhO /PhO-. The potential for the SO₃ - /SO₃^2- couple is found to be (0.73 0.01) V vs NHE. The potential for -SO₅ - /SO₃^5- is found to be (0.81 0.02) V. The reduction potential of the radical formed from the one-electron oxidation of thiosulfate, which exhibits a λ _max at 375 nm, is also determined. This radical was identified as either the monomeric S₂O₃ - or the dimeric S₄O₆ 3 . Equilibrium measurements for this species using N₃ and the 4-cyanophenoxyl radical as references support the dimeric assignment and yield a value of (1.07 0.03) V for the reduction potential for the couple S₄O₆³ - /2S₂O₃²-.

Citation

Journal of Physical Chemistry A

Volume

103

Pub Type

Journals

Keywords

aqueous solutions, kinetics, reduction potential, sulfur oxides

Citation

Das, T. , Huie, R. and Neta, P. (1999), Reduction Potentials of SO₃-, SO₅.-, And S₄O₆.^3- Radicals in Aqueous Solution, Journal of Physical Chemistry A (Accessed May 11, 2024)