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.
The dissociation constants of benzohydroxamic, 4-chlorobenzohydroxamic, and 4-nitrobenzohydroxamic acids, and their N-methyl and O-methyl derivatives, were measured spectrophotometrically or potentiometrically in mixtures of 2-propanol and water. The results were extrapolated to zero ionic strength. The ratio of dissociation constants of the N-methyl and O-methyl derivatives can be taken to represent - with some approximation - the ratio of NH and OH acidities of the parent acid. This ratio increases with substitution by electron-attracting substituents, and decreases with solvent permittivity: some irregularities might be attributable to the effects of mixed solvents, It follows that 4-nitrobenzohydroxamic acid behaves essentially as N-acid in all solvents, 4-chlorobenzohydroxamic acid only in 90% 2-propanol or 80% methyl cellosolve. In benzohydroxamic acid the NH and OH acidities are comparable, the latter prevails slightly in water, the former in less polar solvents. Some apparent discrepancies in the literature can be explained in the same terms, only a few results have not yet been explained.
pK Values of carboxylic acids have been measured in mixtures water-organic solvent and confronted with the Born equation. Solubilities of benzoic acid have been measured. From the pK and solubilities found the ΔGt0(C6H5COO-) values have been calculated for various two-component solvents. The results agree with the idea that the ion transfer into another medium is affected not only by electrostatic, but also by non-electrostatic forces.
The autoprotolysis constants were determined potentiometrically for water-ethanol, water-1-propanol, water-2-propanol, and water-2-methyl-2-propanol mixtures containing alcohol in concentrations of 60% (m/m) and more. Three methods were employed for the calculation of the activity ratios of the lyate ions in the systems: an empirical method based on the autoprotolysis constant and the activities of the solvent constituents, a method based on thermodynamic data, particularly the Gibbs energies of ion transfer from water to the mixed solvent, and a method based on 1H NMR data. The results of the three methods are mutually compared and discussed. The known heats of ionization for the water-ethanol system and the ionization constants of the components enabled the entropy of ionization of a mixture of water with ethanol to be calculated.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.