The Effect of Substituents on the Acid Strength of Benzoic Acid. IV. In Dioxane–Water.

Abstract

This paper extends to mixed solvents the study of the effect of solvent Dioxane-water mixtures permit a study over Minnick and Kilpatrick (10)

Separation of the Enthalpic and Entropic Contributions to Substituent Effects for the Equilibrium Constants of Aromatic Acids

“…The 'right' substituent constants (oO) are proposed for reactions with very low or negligible contribution from resonance interaction. On applying [28] one obtains p, = 86%, that is, 10% higher than that for the reference reaction. Thus, a reaction with low resonance interactions may be described as entropy controlled.…”

Symposium on the Thermodynamics of Electrolytic Dissociation: The Effect of Dielectric Constant on Acid-Base Equilibria.

“…In the earlier work (29) a comparison of the values of KAxBtl for the solvents ethyl alcohol and dioxane-water mixtures of the same dielectric constant showed quite good agreement, and it was concluded that the dielectric constant was the important factor. Further work (10) in dioxane-water mixtures of dielectric constants 55 and 40 has shown that the results are not in accord with equation 21. A few typical results are presented in figure 4, in which the dotted lines represent the line of equation 21 for the pure solvents.…”

“…An examination of the results for the twenty-three acids shows that equation 21 holds in all the pure solvents of dielectric constant > 24, the only exceptions being the ortho acids in the solvent ethylene glycol. Table 3 gives the slopes and intercepts of equation 21, as determined by the method of least squares for all the experimental results in the four solvents (5,7,8,9,10,22,23). Fig.…”

“…are 1.020 for water (dielectric constant = 78.54), 4.02 for methyl alcohol (D = 31.5), 5.97 for ethyl alcohol (D = 24.2), and 9.79 for butyl alcohol (D = 17.4). For more concentrated solutions no theoretical equation can be given, but it might be well to point out that the change in the equilibrium constant Kc is of considerable magnitude and depends on the solvent (10); see table 1. Leaving the correction for the ionic atmosphere, it is seen that the solvent itself and the dielectric constant of the medium play important róles in the process represented by equation ing process, the transfer of the proton involves electrostatic work depending on the dielectric constant, and the solvation of the ions and molecules involves the dielectric constant and the structure of the solvent (4). Equation 3 makes the standard acid the solvated proton, and equation 2 represents the ratio of the dissociation constant of the acid Az to that of the acid SH+.…”

Restriction of Tautomerism in the Amidine System by Hydrogen Bonding. The Case of 4(7)-Nitrobenzimidazole1

“…These pK values for ethanol solutions were calculated from dissociation constants of the acids in ethanol(29)(30)(31)(32) …”