F. Gaillard et E. Levillain, VISIBLE TIME-RESOLVED SPECTROELECTROCHEMISTRY - APPLICATION TO STUDY OF THE REDUCTION OF SULFUR (S-8) IN DIMETHYLFORMAMIDE, Journal of electroanalytical chemistry [1992], 398(1-2), 1995, pp. 77-87
We have studied the reduction of sulfur in dimethylformamide (DMF) by
time-resolved spectroelectrochemistry coupling electrochemical techniq
ues (cyclic voltammetry and chronoamperometry) with intensified multic
hannel detection spectrophotometry. The measurement system allows up t
o 2000 spectra to be recorded in real time during the electrochemical
perturbation and the derivative of absorbance to be calculated at all
wavelengths of the visible range in order to compare electrochemical a
nd spectroscopic measurements. The comparison between experimental dat
a obtained under semi-infinite linear diffusion conditions and under t
hin layer conditions, between -40 and +60 degrees C, shows that S-8 is
reduced to S-8(2-) and that the disproportionation of S-8(2-) is weak
but leads rapidly to the formation of a low concentration of S-3(-).
We show that the reduction prewave, observed at a potential just lower
than that of the reduction of S-8 and assigned by various authors to
acidic impurities, is well resolved under thin layer conditions and gi
ves a high concentration of S-3(-) near the working electrode. This re
duction prewave is interpreted as the reduction of S-8(2-) and/or of i
ts monomer S-4(-).