Voltammetry in Sulfolane: The Electrochemical Behavior of Benzaldehyde and Substituted Benzaldehydes

The electrochemical reduction of a series of para-substituted benzaldehydes in the aprotic solvent sulfolane has been explored by linear sweep and cyclic voltammetry. A single one-electron process is seen for the carbonyl reduction. The potential for the benzaldehyde reduction is shifted cathodically from previously reported potentials in other solvents and the chemical reaction following reduction is slow enough so that the reoxidation of the benzaldehyde intermediate is detectable at a sweep rate of 83.3 mV/sec. Benzaldehydes with an inductive substituent show an enhanced stability of the reduction intermediate. Rate coefficients for the disappearance of the intermediate are presented (e.g., K₂ for the dimerization following reduction of benzaldehyde = 2.4 × 10³ l./m.sec). The contribution of the dielectric constant, and low Bronsted acidity of sulfolane to this reduction behavior is discussed.