The Electrochemical Oxidation of Sesamol in Acetonitrile Containing Variable Amounts of Water

The oxidation of sesamol in acetonitrile was examined in detail via a combination of electrochemical techniques (cyclic voltammetry (CV) and controlled potential electrolysis (CPE)) and chemical oxidation (using NOSbF₆). At a platinum electrode, sesamol undergoes electrochemical oxidation at ca. 0.70 vs. (Fc/Fc⁺)/V and displays a corresponding reduction process at ca. 0.35 vs. (Fc/Fc⁺)/V when the scan direction is reversed after first oxidizing the compound. Results from variable scan rates CV experiments revealed that the reduction process at 0.35 vs. (Fc/Fc⁺)/V increased in current magnitude relative to the oxidation process at 0.70 vs. (Fc/Fc⁺)/V with increasing scan rates. The process at 0.35 vs. (Fc/Fc⁺)/V was assigned to the reduction of a dimeric intermediate species (7) produced by the initial -2e^-/-2H⁺ oxidation of the starting material. Following the addition of iodomethane after the bulk oxidation of sesamol, a neutral dimeric product (8) was isolated and positively identified by X-ray crystallography. A mechanism for the formation of 8 on synthetic timescales (>seconds) was proposed based on the transfer of five electrons per two molecules of sesamol to initially produce a tetrameric radical cation. Both CPE and chemical oxidation measurements support that the anodic process involves the transfer of multiple electrons, with the number of electrons varying depending on the exact concentration of sesamol. The electrochemical oxidation of sesamol was also observed to be influenced by hydrogen-bonding interactions with trace amounts of water in the sample solution.