ELECTROCHEMISTRY AND ELECTROANALYTICAL CHEMISTRY OF THE POLYSULFIDES AND THE POLYTHIONATES

The electrochemistry of the polysulfides and polythionates was investigated at mercury and glassy carbon indicator electrodes. A single composite polarographic current-voltage wave was observed in mixtures of polysulfides at the dropping mercury electrode. The cathodic portion of the wave was accounted for by the electro-; reduction of the polysulfidic sulfur component of the polysulfides via the reaction: (UNFORMATTED TABLE FOLLOWS); S(,x)('2-) + 2(x-1)e + xH('+) = xHS('-) (1)(TABLE ENDS); The annodic portion of the wave was due to the anodic depolariza- tion of mercury, viz., (UNFORMATTED TABLE FOLLOWS); S(,x)('2-) + xHg = xHgS + 2e (2)(TABLE ENDS); The first comprehensive investigation of the polarography of hexathionate is reported. Two cathodic current-voltage waves were; observed at the dropping mercury electrode in aqueous solution, corresponding to the electroreduction processes: (UNFORMATTED TABLE FOLLOWS); S(,6)O(,6)('2-) (.) aq + 2e + 2Hg = 2S(,2)O(,3)('2-) (.) aq + 2HgS (.) ads (3); S(,6)O(,6)('2-) (.) aq + 6e + 4H('+) = 2S(,2)O(,3)('2-) (.) aq + 2H(,2)S (4)(TABLE ENDS); This compared with the following electroreduction reactions of trithionate, tetrathionate, and pentathionate. (UNFORMATTED TABLE FOLLOWS); S(,3)O(,6)('2-) + 2e = S(,2)O(,3)('2-) + SO(,3)('2-) (5); S(,4)O(,6)('2-) + 2e = 2S(,2)O(,3)('2-) (6); S(,5)O(,6)('2-) + 2e + Hg = 2S(,2)O(,3)('2-) + HgS (7); S(,5)O(,6)('2-) + 4e + 2H('+) = 2S(,2)O(,3)('2-) + H(,2)S (8)(TABLE ENDS); The corresponding polarographic waves of tetrathionate and pentathionate overlapped in aqueous solution. However, if the sol- vent was changed to an ethanol (40% v/v)-water (60% v/v) mixture, the tetrathionate was shifted cathodically by 1.1 volt, obviating the overlap.