Control of the electrochemical reduction of horminone by pH imposition in acetonitrile

An electrochemical study using transient techniques of a quinone-type natural product, horminone, has been performed in acetonitrile in the presence of two buffer solutions of pH = 17.2 and pH = 15.5. Using linear sweep voltammetry, it was found that at both pH values the reduction mechanism of horminone involves a monoelectronic charge-transfer step, followed by a protonation step and homogeneous charge-transfer step due to disproportionation of the protonated intermediate. At pH = 15.5 the mechanism for the homogeneous charge-transfer step was found to be of the DISPl type (first order disproportionation) from the results of double step chronoamperometry experiments. At pH = 17.2 the latter mechanism was found to be of the DISP2 type (second order disproportionation) since at this pH value the protonation step is minimized, thus causing the disproportionation reaction to be the controlling step of the mechanism.