Since the original report by Mairanovskii and Neimanl,. several groups have investigated the electrochemistry of sulfones; however, most of the work has been in protic solvents. In such media the mechanism for the reduction of diphenyl sulfone is generally reported to be a two electron transfer with a coupled cleavage of a C-S bond to produce benzene and benzenesulfinic acid 2-4.
Manousek et al. 5 studied a series of substituted methylphenyl sulfones. They demonstrated that the C-S bond preferentially cleaves to produce the alkylsulfinic acid when electron-attracting substituents are placed on the phenyl ring. In a related study performed in dimethylformamide (DMF), Simonet and Jeminet found that when the substituent is an electron donor, the bond preferentially cleaves to produce the substituted arylsulfinate ion 6.
The latter also noted that the substituted arylsulfinic acids produced undergo a further one electron reduction at a potential more positive than the sulfone precursor. Likewise, benezenesulfinic acid was reduced at a potential 30 mV positive of the reduction ofmethylphenyl sulfone. When phenol or acetic acid was added to the DMF, no reduction was observed prior to the breakdown of the supporting electrolyte.
Recently Gerdil 7 reported that the polarographic reduction of diphenyl sulfone in anhydrous DMF proceeds in two steps: a one electron reduction to form a radical anion followed by formation of the dianion at a more negative potential. Previously Gerdil and Lucken s had shown that the product of the one electron reduction at -70Β°C is a radical anion by e.s.r, using controlled potential electrolysis to generate the species in the spectrometer cavity. Kaiser et al. 9 generated the radical anion of diphenyl sulfone by reduction with potassium at -70Β°C in dimethoxyethane. They found that at higher temperatures the radical anion was too unstable for their e.s.r, study.
The present study was initiated to determine the detailed mechanism for the electrochemical reduction of diphenyl sulfone in aprotic solvent under conditions where the radical anion is unstable. Polarography and cyclic voltammetry were used to establish the mechanism, and the kinetics of the coupled chemical reactions were investigated by potential step chronoamperometry.
EXPERIMENTAL
The electrochemical experiments were performed with a three electrode solid