Kinetics of aromatic nucleophilic substitution by toluene-p-thiolate in dimethylformamide. Effect of solvent on Hammett-type correlations

The kinetics of the reaction of some 4-substituted 2-nitrochlorobenzenes with toluene-p-thiolate in dimethylformamide have been measured at temperatures from -39.7 to 71.9°C. Correlation of rates by Hammett-type equations gives, using the best set of σ values, ρ = +6.65 at 10°C. The dependence of the ρ value on the solvent is discussed. A comparison of these reactions with those of Ar2C=CHCl and of ArC≡CCl with the same nucleophile-solvent system shows that the substituent effects are markedly attenuated by the interposition of C=C or C≡C bonds.