Potentiometric titration has been used to measure dissociation constants of 38 monosubstituted benzoic acids in water and in 6 organic solvents (methanol, ethanol, dimethylformamide, acetonitrile, sulfolane, acetone). The results have been analyzed and interpreted from the point of view of substituent and solvent effects on the dissociation of the title substrates. It has been proved that solvents affect not only the reaction constant but also the substituent constant of the Hammett equation.

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Thirteen monosubstituted arylsulphonamides (XC6H4SO2NH2) and two 3,4-disubstituted arylsulphonamides (X2C6H3SO2NH2) have been synthetized and their dissociation constants have been measured by potentiometric titration in water, methanol, and ethanol. The Hammett substitution dependences have been calculated for all the media, and changes in the reaction constants due to transition from water to alcohols are discussed in confrontation with analogous dependences of benzoic acids. The reaction constant ρ found in methanol is lower than that in water. The dissociation constants have been treated mathematically by the method of the principal components and by multiple linear regression.

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Dissociation constants of fifteen substituted arenesulphonamides of general formula XC 6 H 4 • . S02NH2 (or X2C6H3S02NH2) have been measured by potentiometric titration in dimethylformamide, dimethyl sulphoxide, and acetonitrile. The Hammett substitution correlations have been calculated and interpreted for these media. The pK HA values measured and the results published earlier for methanol, ethanol, and water have been treated by multiple linear regression using the published set of the parameters characterizing solvents and by factor analysis using the short cycle and the target testing method.• Purification of solvents: Dimethyl sulphoxide and acetonitrile were purified according to Kolthoff 17 .18. Dimethylformamide was repeatedly distilled in vacuum in the presence of fused powdered potassium hydroxide. Traces of alkalis were removed by two subsequent vacuum distillations, and the solvent was dried by keeping over activated molecular sieve for 14 days.Preparation of tetrabutylammonium nitrophenoxides: Picric acid, 2,4-dinitrophenol, and 2,6-dinitrophenol were dissolved in methanol. The solutions were neutralized with 0·1 moll-1 tetra-

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The dissociation constants measured earlier for 35 substituted benzoic acids in seven solvents (water, methanol, ethanol, dimethylformamide, acetonitrile, sulfolane, and acetone) have been submitted to the principal components analysis and the factor analysis to produce sets of the Hammett substituent constants. The solvent effects have been evaluated on the dissociation constants of the substituted benzoic acids and, hence, also on the respective substituent constants. He differences have been compared between the substituent constants determined by the principal components analysis and by the factor analysis, the latter being found to be more suitable. The obtained sets of substituent constants have been confronted with literature data, and an excellent agreement has been found between the σ constants derived from the measurements in water with the sets of primary substituent constants and some other sets.