Electrochemical and ESR study on the transformation processes of α-hydroxy-quinones

The electrochemical analysis by cyclic voltammetry and double potential step chronoamperometry of two α-hydroxyquinones (2-hydroxy-1,4-naphthoquinone and perezone) in acetonitrile, reveals that in the first electron transfer process, self-protonation reactions are present. One of the products of this reduction is the deprotonated original quinone. This last intermediate is reduced by a monoelectronic process in the second reduction step, generating a radical dianion. The radical dianions formed can be detected by EC-ESR coupled experiments and the spectra characteristics were explained in terms of the electron delocalization properties of the analyzed compounds. Upon the addition of a base (tetrabutylammonium hydroxide), the ESR signal increases in intensity and hyperfine coupling analysis is better resolved, proving the radical nature of such species. The oxidation properties of the deprotonated quinone of 2-hydroxy-1,4-naphthoquinone were also studied under these basic conditions. The results provide insights into the proposal of a dimerization process occurring in this oxidation process.