Analysis of substituent and solvent effects on dissociation of N-phenylbenzenesulphonamides

Abstract

The potentiometric titration in water, methanol, dimethyl sulphoxide, dimethylformamide, and acetonitrile has been used for determination of pK values of 13 N-arylbenzenesulphonamides. The validity of the Hammett and Yukawa-Tsuno models using several sets of substituent constants has been evaluated by the test to check adequacy of the regression function and by the factor analysis. It has been found that the substituent effects in solvents must be interpreted with regard to the experimental method used, solvent, set of the substituent constants, as well as the model equation ETR. The dependence of the Hammett reaction constants on the solvent has been analyzed and reveals a preferred stabilization of the conjugated base through hydrogen bonds. Direct conjugation of the reaction centre with the substituent and with different extent of the solvent-dependence with the 4-CN and 4-NO2 derivatives have been observed.