This note reports on the electrochemical oxidation in acetonitrile of bis-(phenylthio)-methane, a biphenyl mercaptal. In the presence of either sodium or tetraethylammonium perchlorate this compound is cleanly oxidized to diphenyldisulfide and formaldehyde at a platinum electrode. This result is unique*. In nonaqueous solvents sulfides have been found to form sulfonium ions 1-3 or to undergo oxidative fragmentation reactions 4,s upon anodic electrolysis. In the presence of water or in acidic solutions, sulfoxides, sulfones, and sulfonic acids are usually formed 6,7 .
Cyclic voltammograms of bis-(phenylthio)-methane (1) exhibit two closely, spaced irreversible oxidation waves at 1.46 V and 1.57 V vs. SCE at slow sweep rates (0.048 V s -1 ). In addition a drawn-out current hump is usually present on the tail of the second peak. The current function, ip/Ac ~rv, of the first wave is ca~ 2.5 A 1 sY2 cm -2 mol-~ V -'A. Both the peak potentials and the current function are dependent on sweep rate and the waves merge at sweep rates greater than ca~ 0.3 V s-~. Due to the proximity 'of the two waves careful electrolysis is required to obtain a coulometric n-value for the first wave. The linear sweep voltammograms in Fig. 1 show the progress of an electrolysis in which the applied potential was maintained at the foot of the first wave. The measured electrode potential (1.38 V vs. SCE) at a platinum electrode in a three compartment cell is shown by the arrow. At the completion of the electrolysis (curve 6) the first wave has disappeared. In this manner a coulometric n-value of 2.1 was obtained for the process which corresponds to the first wave.
The major electrode products were isolated and identified. Diphenyldisulfide was obtained in a 66% yield in dry acetonitrile and identified by comparison of its melting point, n.m.r., infrared and mass spectra with the literature and standard spectra. No attempt was made to maximize the yield. Suspected formaldehyde was precipitated as its dimedone adduct s by the following procedure. Water was added to a concentrated *When this paper was in preparation, we learned that Simonet and co-workers have obtained similar results 14.