The dissociation constants of nicotinic, picolinic, benzoic, and o-, m-, and p-aminobenzoic acids and those of glycine, dl-alanine, β-alanine, aniline, and pyridine were determined potentiometrically and spectrophotometrically in 0, 10, 30, 50, and 72% (w/w) ethanol–water mixtures at 25 °C at various ionic strengths (0.01–0.5 mol dm−3). The pK’s of benzoic, o-, m-, and p-aminobenzoic acids increased with increase of EtOH contents while those of nicotinic acid, picolinic acid, glycine, dl-alanine, and β-alanine passed through minimum (upto 30% w/w EtOH contents). The pK’s of aniline and pyridine were almost the same as those found in literature. The variation in pK’s with the solvent composition is discussed in terms of the free energy of transfer from H2O to EtOH–H2O mixtures. The zwitterion to neutral molecule ratio of these acids is also discussed in terms of variation of composition of mixtures.

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The thermodynamic dissociation constants and the limiting molar conductivities of 2-, 3-, and 4-nitrobenzoic and benzoic acids have been determined in water–acetonitrile mixtures at 298 K. It is found that the acids dissociate in the dereasing order as 2-nitrobenzoic acid > 3-nitrobenzoic acid≈4-nitrobenzoic acid > benzoic acid. The conductance–concentration data were analyzed with the Lee and Wheaton equation. The present results are compared with the previous ones for these acids in alcohol–water system, and are interpretted in terms of solute–solvent interactions, intramolecular hydrogen bondings, resonance and inductive effects along with the substituent position.

The dissociation constants and limiting molar conductances of benzoic and 2-, 3-, and 4nitrobenzoic acids have been determined in binary mixtures of water with acetone and tetrahydrofuran at 25 "C, respectively. The experimental data were analyzed by means of the Lee and Wheaton equation. The results are compared with those available in literature and in other water + cosolvent mixtures.

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