Relative nucleophilicities of aryldisulphide and thiolate ions in dimethylacetamide estimated from their reaction rates with alkyl halides

Abstract

The relative rates of nucleophilic substitution (S_N2) of alkyl halides by aromatic thiolates ArS^– and aryldisulphide ions ArS₂^– have been studied in dimethylacetamide by UV–visible spectrophotometry for Ar = 4-nitrophenyl (1), 2-nitrophenyl (2), and 8-quinolyl (3). Rate constants are relative to the rate constants for benzenethiolate ions (4), studied as reference. With Ar =(1), the reaction rate for disulphide ions is ten times higher than that for monosulphide ions stabilized by the elevated delocalization of their charge. With Ar =(2) and (3), the reactivity of disulphide ions is higher than that of the corresponding thiolates. Our study is consistent with the uncomplicated introduction of a disulphide bond into various substrates from aryldisulphide ions stabilized in aprotic dipolar media.