Displacement of aromatic nitro groups by anionic sulfur nucleophiles: reactivity of aryl disulfide and thiolate ions towards dinitrobenzenes in N,N-dimethylacetamide

Nucleophilic substitutions of 1,2- and 1,4-dinitrobenzenes (oDNB and pDNB) by thiolates ArS–(a) and aryl disulfide ions ArS2–(b)[Ar = 4-methylphenyl (1), 4-fluorophenyl (2)] have been studied in dilute solutions by spectroelectrochemistry in N,N-dimethylacetamide. Compounds 1b–2b are the predominant reactive species in ArSx–(x= 2) solutions when sulfur is added to electrogenerated thiolates 1a–2a. In all cases the addition of dinitrobenzenes led to the fast displacement of one of the NO2 groups at room temperature. With thiolate ions, the stoichiometric formation of the expected unsymmetrical diaryl monosulfides NO2C6H4SAr was observed. Aryl disulfide ions reacted in two successive steps: (i) SNAr substitution affording NO2C6H4S2Ar; (ii) displacement of NO2C6H4Sx– ions (x= 1,2) by S-nucleophilic attack of the S–S bond or a concurrent redox process. Reactions between 4-CH3C6H4Sx–(x= 2) ions and oDNB or pDNB which were performed on the preparative scale confirmed the formation of mixtures of Ar2S2 and Ar2S3 symmetrical polysulfides.