Studies on the electrochemical reduction and coupled homogeneous reactions of cinnamaldehyde in acetonitrile

An in-depth investigation on the redox reactions of cinnamaldehyde in acetonitrile was carried out using cyclic, linear sweep, and rotating disk electrode voltammetry in conjunction with controlled potential electrolysis and digital simulations. Overall, it was found that cinnamaldehyde displays a similar reduction behavior to retinal (an aldehyde form of vitamin A), and can be reduced by two consecutive one-electron processes to initially form its radical anion (E_p^red ≈ − 1.95 vs. (Fc/Fc⁺)/V, where E_p^red refers to the cathodic peak potential and Fc = ferrocene), and then its dianion (E_p^red ≈ − 2.50 vs. (Fc/Fc⁺)/V). Both reduction processes had limited chemically reversibility even when examined at relatively fast scan rates and low temperatures. Notably, voltammetry and electrolysis experiments revealed that the electrochemical reduction critically depends on the amount of cinnamaldehyde used. At high concentrations, the radical anions have a propensity to undergo a heterodimerization reaction with the starting material to form a radical anionic dimer which could be voltammetrically detected at fast scan rates. Nevertheless, the experimental data also indicated a number of other homogeneous reactions involving the reduced species (radical anion and dianion) which were modeled by digital simulations to determine the electrochemical and kinetic parameters affiliated with all of the heterogeneous electron transfer and homogeneous reaction steps.