On the understanding of the reduction of sulfur (S-8) in dimethylformamide (DMF)

We have re-examined, using cyclic voltammetry, the electrochemical reduction of sulfur in DMF. The main purpose of this work is the determination of the electrochemical mechanism of this reduction and the identification of the opening step of the ring S-8. We propose the following electrochemical mechanism which neglects the weak disproportionation of S-8(2-): S-8c + e(-) reversible arrow S-8(c-) (E-c) S-8c(-) reversible arrow S-81(-) (K-1) S-81(-) + e(-) reversible arrow S-81(2-) (E-1) and E-1 > E-c S-8c(-) + S-81(-) reversible arrow S-8c + S-81(2-) (K-2 = exp[(F/RT)(E-1-E-c)]) This mechanism (ECE) takes into account the ring character (c) of sulfur in the solution and the linear character (1) of the S-8(2-) polysulfide. It has been simulated and adjusted to the experimental data in a wide range of temperatures (233 to 313 K) and scan rates (50 to 2000mVs(-1)). We shall discuss the choice of this mechanism and the results.