One-Electron Redox Potentials of Phenols in Aqueous Solution

The oxidation peak potentials ( E p ) of 31 phenolate, chlorophenolate, and other para-substituted phenolate ions were measured as a function of scan rate, substrate concentration, and pH by cyclic voltammetry in aqueous solution. The one-electron reduction potentials ( E red o ) of the phenoxyl radical/phenolate ion couples were evaluated from E p and the rate constants for dimerization of the phenoxyl radicals. The dependence of E red o on pH was established, and the relationships that connect E red o with the Brown σ + constant, the p K a values of the phenols and the protonated phenoxyl radical cations, and the reduction potentials of the protonated radicals were explored.