Oxidation of Benzoatopentaamminecobalt(III) by Hydroxyl Radicals

The reaction of hydroxyl radicals with benzoatopentaamminecobalt(III) yields a radical formed by the addition of the OH to the aromatic ring. The spectrum of the radical formed is very similar to that formed by the reaction of OH radicals with free benzoate ions. The specific rates of formation and disappearance of the radical were measured. The disappearance follows a second-order mechanism. The yield of Co²⁺ depends on the steady-state concentration of the radicals formed and is always considerably less than one, based on the concentration of OH radicals introduced. It is concluded that the overlap between the orbitals on the central Co(III) atom and the conjugated double bond system of the radical is small. Furthermore, if an inner-electron transfer from the radical to the central Co(III) atom takes place, the specific rate of this reaction is less than 10² sec^-1.