Self-protonation mechanism in the electrochemical reduction of Jatropholone

Abstract

Abstract The electrochemical reduction mechanism of jatropholone (JOH) and derivatives (JOAc) was investigated by cyclic voltammetry, polarography, coulometry and controlled potential electrolysis. It involves at the first wave potential, a self-protonation mechanism, whereby the two-electron reduction product (JOHH − ), an aromatic ketone, is formed together with the conjugate base of the former compound, JO − . The unusual stoichiometry of the cathodic process at the first wave, 1 mol electron mol −1 , indicates that JOHH − is not further protonated. The decreased basicity of the anion is due to resonance stabilisation. The second wave is related to the reduction of JO − and further reduction of JOHH − , that has a reminiscent electroactive group. In the latter case, the background electrolyte is liable to be the proton donor, through Hoffman elimination. The complete reduction involves 4 e − and 4 protons. Electrolysis performed near the first wave potential led to the almost exclusive reduction of the exocyclic double bond, without dimerization.