Nucleophilic substitution of alkyl halides by electrogenerated polysulfideions in N,N-dimethylacetamide

The reactions between a series of alkyl halides RX: X = I, R = CH3 (1), C3H 7 (2); X = Br, R = C4H9 (3), 2-C4H9 (4), 3-C5H11 (5), PhCH2 (6); X = Cl, R = PhCH2 (7), C6H13 (8), and electrogenerated S1/3- ions (S-6(2-) reversible arrow S-3(.-)) have been investigated by spectroelectrochemistry in N,N-di methylacetamide at 20 degrees C. RX substrates react in two steps: (i) nucl eophilic substitution of S1/3- ions (S(N)2 process) yielding RSx- ions ((x) over bar = 5.2, R = alkyl; (x) over bar = 4.8, R = PhCH2); (ii) subse quen t substitutions of RS; ions lead to RS,R polysulfanes ((z) over bar approxi mate to 3.5), probably through partial disproportionation of the anionic sp ecies. On a preparative scale, mixtures of CH3SzCH3 (z = 2-6, (z) over bar = 3.9) or PhCH2SzCH2Ph (z = 2-5, (z) over bar = 3.7) were obtained from che mical reactions between 1, 6 and S-6(2-) ions, or electrochemical syntheses . Kinetic studies at 20 degrees C of the reactions between S-3(.-) ions and substrates 4, 5, 7 and 8 imply that the dianions S-6(2-) are the nucleophi lic agents in the first step rather than S-3(.-) radical anions.