Reduction Potentials of SO3-, SO5.-, And S4O6.3- Radicals in Aqueous Solution
T N. Das, Robert E. Huie, Pedatsur Neta
Reduction potentials of the SO-3 -, SO5 -, and S4O63- 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 -/SO32- and SO5 - /SO52- 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 - /SO32- couple is found to be (0.73 0.01) V vs NHE. The potential for -SO5 - /SO35- 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-.
, Huie, R.
and Neta, P.
Reduction Potentials of SO<sub>3</sub>-, SO<sub>5</sub>.-, And S<sub>4</sub>O<sub>6</sub>.<sup>3-</sup> Radicals in Aqueous Solution, Journal of Physical Chemistry A
(Accessed December 3, 2023)