NUCLEOPHILIC-SUBSTITUTION OF NITROAROMATIC HALIDES BY ELECTROGENERATED POLYSULFIDE IONS IN DIMETHYLACETAMIDE

Electrogenerated polysulphide ions S3.- and S8(2-) readily react with haloaromatics, ArX, activated by nitro electron-withdrawing substituents in dimethylacetamide. Nucleophilic substitutions on fluoro-2,4-dinitrobenzene (1a; X = F), halo-4-nitrobenzenes (2a; X = F, Cl, Br, I) and 2-nitrobenzenes (3a; X = F, Cl, Br, I) lead to the coloured arylmonosulphide (1b; X = S-) and aryldisulphide (2c-3c; X = S2-) ions. From the reaction kinetics studied by UV-VIS spectrophotometry, the order of reactivity is ArF > ArBr, Arl > ArCl. The proposed S(N)Ar mechanism implies that the dianions S6(2-) and S8(2-) are the nucleophilic agents (S6(2-) much-greater-than S8(2-)) rather than the S3.- and S4.- radical anions.