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

Abstract

The relative rates of nucleophilic substitution (SN2) 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.