POLYSULFIDES IN DIMETHYLFORMAMIDE - ONLY THE REDOX COUPLES S-N(-) S-N(2-) INVOLVED/

The redox mechanism of polysulfides in nonaqueous solvents is examined , For that purpose, Li2S6 + DMF solutions have been investigated by us ing cyclic voltammetry and time-resolved spectroelectrochemical experi ments coupling spectrophotometry and cyclic voltammetry. It is shown t hat the only redox couples involved in these solutions are S-n(-)/S-n( 2-) with n = 3,4,6,8 and S-8c/S-8c(-) (c for cyclic). The experimental results are interpreted by the following mechanism: [GRAPHICS] This m echanism has been simulated and adjusted to the experimental voltammog rams in broad temperature (233 to 313 K) and scan rate (50 to 2000 mV/ s) ranges, recorded for an initial scan in the positive direction and in the negative direction. We have obtained a complete description of the redox properties of sulfur and polysulfides in this solvent. We ha ve shown that only the radical anions S-n(-) are reducible and that on ly the dianions S-n(2-) are oxidizable. It is also shown that this mec hanism describes the two steps of the reduction mechanism of sulfur in DMF. (C) 1997 Elsevier Science S.A.