Nucleophilic substitution of nitroaromatic halides by electrogenerated polysulphide ions in dimethylacetamide

Abstract

Electrogenerated polysulphide ions S˙₃^– 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_NAr mechanism implies that the dianions S₆^2– and S₈^2– are the nucleophilic agents (S₆^2– S₈^2–) rather than the S˙₃^– and S˙₄^– radical anions.