Electron transfer to sulfides: Heterogeneous kinetics, C-S bond cleavage, and self-protonation

摘要

The problem of characterizing the steps associated with the dissociative reduction of sulfides has been addressed. The electrochemical reduction of diphenylmethyl para-methoxyphenyl sulfide in Af,Af-dimethylformamide, on both glassy carbon and mercury electrodes, Vv chosen as a test system. The electrode process involves the slow heterogeneous outer-sphere electron transfer to the sulfide, the fast cleava of the C-S bond, the reduction of the ensuing carbon radical, and the self-protonatipn triggered by the generation of the strong base Ph{sub}2CH{sup}- The latter reaction is rather slow, in agreement with the large intrinsic barriers characterizing proton transfers between CH-acids and carb bases. The dissociative reduction was studied in the presence of an exogenous acid. The results, obtained by convolution analysis, point a stepwise DET mechanism in which the ET step is accompanied by rather large reorganization energy. Similar results were obtained both electrode materials. Analysis of the heterogeneous electron transfer and associated C-S bond cleavage indicate that the reduction of tl and other sulfides lies between the stepwise dissociative electron transfers leadihg to the formation of stiff TV* radical anions and those goi: through the intermediacy of loose σ radical anions.