Rotating Ring-Disk Electrode Studies of the Electrochemistry of Aromatic Carbonyl Compounds in the Solvent Sulfolane

The method of rotating ring-disk voltammetry has been applied to the study of the reduction of benzaldehyde and para-substituted benzaldehydes in sulfolane. Benzaldehyde undergoes an EC reduction mechanism with an anion dimerization as the following reaction. Digital simulation techniques give values of the second order rate coefficients of k2 = 2.4 x 103 liters/mole-sec. Para-cyanobenzaldehyde undergoes a mixed reduction mechanism. At low disk currents the reduction intermediate is proposed to be a parent-anion complex. At higher fluxes, dimerization becomes the significant following process; k2 = 45 liters/mole-sec. A single electroactive intermediate is observed for the first one-electron reduction of p-nitrobenzaldehyde. The single, chemically, reversible redox mechanism for this compound in sulfolane agrees with our spectroelectrochemical results.