FORMATION AND SCISSION OF THE SULFUR-SULFUR BOND - A NEW APPROACH TO REACTIONS BETWEEN SULFUR POLYSULFIDE IONS AND THIOLATE IONS/DISULFIDESIN N,N-DIMETHYLACETAMIDE/

The reactivity of sulfur towards a series of thiolate ions RS(-) [R = phenyl (1), 4-methylphenyl (2), benzyl (3) ethyl (4), propyl (5), buty l (6), sec-butyl (7), tert-butyl (8)] has been studied by spectroelect rochemistry in N,N-dimethylacetamide. Apparently, sulfur reacts in two parallel ways: (i) oxidation of RS(-) leading to RS(2)R and S-3(.-) i ons; (ii) preponderant S-nucleophilic process yielding stable RS(x)(-) ions (x = 2-5). RS(x)(-) species, whose spectrophotometric characteri stics have been determined, are successively obtained in the course of sulfur addition with R = alkyl, whereas equilibria between arylpolysu lfide ions were observed. At the junction of these two parallel pathwa ys, the slow key-equilibrium 2RS(4)(-) reversible arrow RS(2)R + 2S(3) (.-) has been investigated by addition of RS(2)R R = 1-8 to S-3(.-) so lutions. In fact, our study is consistent with at first, a monoelectro nic transfer between RS(-) (or RS(2)(-)) ions and the very reactive S- 2 molecules in equilibrium with S-8. The fast and competing couplings of the radicals RS(.) (or RS(2)(.)), S-2(.-) (or S-3(.-)) agree with t he simultaneous formation of RS(2)R, RS(x)(-) and polysulfide ions. Mo re generally, the S-2/S-2(.-) redox system is believed to be involved in thiophilic reactions of a number of anions such as RS(-) towards su lfur rather than the initial opening of the cyclic S-8 form.