A cyclic voltammetric study of some 4-substituted Benzene-1,2-diols

A voltammetric study of several 4-substituted benzene-1,2-diols in aqueous solutions as a function of pH has been carried out. From slow linear sweep voltammetry at a rotating disc electrode, diffusion coefficients were obtained which could be correlated, in the main, with molecular size. From cyclic voltammetry at a stationary electrode, it was established that the rate of the redox reaction decreases with increasing pH. The cyclic voltammetric measurements were also used to estimate E1/2 as a function of pH. All systems studied showed regions in which plots of E1/2 against pH were linear with a slope of close to -59 mV per pH unit. Such plots were used to estimate values of E1/2 at pH 0, which were then correlated with the Hammett function. The cyclic voltammetry also showed that the reactivity of the quinone formed by oxidation of the benzene-1,2 diols increased with pH. With the most reactive quinones (e.g. that formed from 3,4-dihydroxyacetophenone), a second pair of cyclic voltammetric peaks could be observed, which were ascribed to the oxidation and reduction of a dimer formed by quinone coupling.