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

Abstract

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 ArS_x^–(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 NO₂C₆H₄S_x^– ions (x= 1,2) by S-nucleophilic attack of the S–S bond or a concurrent redox process. Reactions between 4-CH₃C₆H₄S_x^–(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.