Electron transfer reaction rates and equilibria of the carbonate and sulfate radical anions

Abstract

Electron transfer reactions of the carbonate radical anion with azide, bromide, and hypochlorite ions have been studied by pulse radiolysis. From the equilibrium Br .- 2 + CO 2- 3 ⇆ 2Br - + CO .- 3 and the known redox potential for Br .- 2/2Br - = 1.62V vs NHE we derive E = 1.59V for CO .- 3/CO 2- 3. From this value and the equilibrium CO .- 3 + ClO - ⇆ CO 2- 3 + ClO . we derive E = 1.41V for ClO ./ClO -. The equilibrium reaction SO .- 4 + Cl - ⇆ SO 2- 4 + Cl . was studied by laser photolysis, by using 248 nm excitation of S 2O 2- 8 to produce SO .- 4 and examining the rate of reaction of this radical with Cl - in the presence of varying concentrations of SO 2- 4. By modeling the reactions taking place in this system, we derive the rate constant for the reaction of Cl . with SO 2- 4 (2.5 × 10 8dm 3mol -1s -1 at 0.1 mol dm -3 ionic strength), and from the known rate constant for reaction of SO .- 4 with Cl - (4.7 × 10 8dm 3mol -1s -1 at the same ionic strength) we derive the equilibrium constant. From the known redox potential for Clf .- 2/Cl - = 2.41V we derive E = 2.43V for SO .- 4/SO 2- 4.