The thermodynamics of the ionization of 3-hydroxypyridine and pyridoxine in water–dioxane mixtures

A potentiometric method has been used to determine the thermodynamic equilibrium constants for the macroscopic ionization processes of 3-hydroxypyridine and pyridoxine in water–dioxane mixtures (0–70% weight fraction in dioxane) at temperatures from 10 to 50 °C. From these data the reaction standard thermodynamic function changes were obtained for the processes in various water–dioxane mixtures at 25 °C. It was found, in both molecules, that during the first ionization process the contributions of entropy and enthalpy to free energy are similar but that during the second ionization the main contribution comes from entropy, especially in mixtures with a high dioxane content. The effect of the solvent on the tautomeric equilibrium in the net zero charge specie could explain this behaviour.

Solubility of water in vinyl chloride

The solubility of water in liquid vinyl chloride has been measured over the temperature range −17° to 60 °C by a classical water absorption method. Solubility equations for water in vinyl chloride have been derived and the standard thermodynamic function changes for water transfer have been evaluated.

Aqueous Nonelectrolyte Solutions. Part VIII. Deuterium and Hydrogen Sulfides Solubilities in Deuterium Oxide and Water

A new apparatus is described in which the solubility of deuterium sulfide in deuterium oxide and of hydrogen sulfide in water have been determined with 0.1 % accuracy between 0 and 50 °C. Solubility equations are derived and the solubility standard thermodynamic function changes, together with their standard errors, are tabluated. Equal solubilities would occur at −1 °C. The solubility of hydrogen sulfide in water is greater than for deuterium sulfide in deuterium oxide, the solubility difference increases to a maximum at 40 °C and thence decreases at higher temperatures.

Deuterium and hydrogen sulfides: vapor pressures, molar volumes, and thermodynamic properties

An apparatus is described in which deuterium and hydrogen sulfides have been prepared by the hydrolysis of aluminum sulfide. Liquid densities have been determined at −79 °C and give the molar volumes 34.811 ± 0.003 cm3 for deuterium sulfide and 34.711 ± 0.003 for hydrogen sulfide. Vapor pressures of deuterium and hydrogen sulfides have been determined at −78 °C in a quartz–metal apparatus, and in the range −30 to +30 °C in a stainless steel apparatus. Equations are derived for the deuterium and hydrogen sulfide vapor pressures and for their ratio. An isotopic vapor pressure cross-over point is found at −48 °C, above which deuterium sulfide is more volatile than hydrogen sulfide. Gas and liquid molar volumes and enthalpy changes are evaluated for liquid vaporization at saturation. The deuterium and hydrogen sulfide vaporization standard thermodynamic function changes and their errors, together with the isotopic differences for these functions and their errors, are tabulated between −80 and +50°C.