Substituent effect on polarographic reduction of aryl diphenylmethyl sulphides in NN-dimethylformamide

Abstract

Aryl diphenylmethyl sulphides, XC₆H₄(X′C₆H₄)CH–S·C₆H₄Y, are reduced polarographically in NN-dimethylformamide in an irreversible two-electron process with fission of the C–S bond. The interpretation of the polarogram is complicated by a reaction of the reduced species with the unreduced depolarizer (autoprotonation effect). The extent of this effect varies with the substituents and can be eliminated by addition of phenol. The polar effects of substituents X and Y as measured by Hammett σ constants are correlated with the half-wave potentials, giving two distinct correlations with different ρ values. Analysis of this substituent effect has allowed us to show how the C–S bond is modified in its charge character at the transition state thereby defining the actual reaction site. The suggested mechanism for the reduction is supported by controlled-potential electrolysis and e.s.r. experiments.