ON THE UNDERSTANDING OF THE REDUCTION OF SULFUR (S-8) IN DIMETHYLFORMAMIDE (DMF)

We have re-examined, using cyclic voltammetry, the electrochemical red uction of sulfur in DMF. The main purpose of this work is the determin ation of the electrochemical mechanism of this reduction and the ident ification of the opening step of the ring S-8. We propose the followin g electrochemical mechanism which neglects the weak disproportionation of S-8(2-): S-8c + e(-) reversible arrow S-8(c-) (E-c) S-8c(-) revers ible 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) a nd scan rates (50 to 2000mVs(-1)). We shall discuss the choice of this mechanism and the results.