Vapor pressure and sublimation thermodynamics of aminobenzoic acid, nicotinic acid, and related amido-derivatives

The inert gas transpiration technique was used for measuring the vapor pressures of the following biologically active compounds: 4-aminobenzoic acid, nicotinic acid, 4-aminobenzamide, 4-pyridinecarboxamide, N -(2-chloro-3-pyridinyl)-benzenesulfonamide, 4-nitro- N -2-thiazolyl-benzenesulfonamide, and 4-amino- N -(5-methyl-3-isoxazolyl)-benzenesulfon-amide in the appropriate temperature ranges. Differential scanning calorimetric analysis was applied to obtain the temperature and molar enthalpy of melting of the compounds studied. Standard molar enthalpies, entropies, and Gibbs energies of sublimation were derived at T = 298.15 K from the temperature dependences of the vapor pressure of the compounds. The obtained results allowed the estimation of the relationship between the sublimation thermodynamic parameters and the thermophysical properties of the substances. Correlation equations were used for calculating the saturated vapor pressures on the basis of the melting temperatures, sublimation enthalpies, and physicochemical HYBOT descriptors.