Vapor pressures and standard molar enthalpies, entropies and Gibbs energies of sublimation of three 4-substituted acetanilide derivatives

The vapor pressures of three 4-substituted acetanilide derivatives (namely, 4-ethoxyacetanilide, 4-hydroxyacetanilide and 4-bromoacetanilide) were measured above their liquids using the mass loss rates determined by thermogravimetry under both isothermal and nonisothermal diffusion-controlled conditions. The coefficient used to convert mass loss rates in vapor pressures showed a slight increase with increasing temperature. Therefore, the small deviations observed from the mean value enable the use of a single calibration value to be considered reasonable. From the temperature dependence of the vapor pressure estimated using a calibration constant for each technique the molar enthalpies of vaporization Δ l g H m ° ( T ) were determined, respectively, at the middle 〈T〉 of the respective temperature intervals. The melting temperatures and the molar enthalpies of fusion of these compounds were measured by differential scanning calorimetry. Finally, the standard molar enthalpies of sublimation Δ cr g H m ° ( 298.15   K ) were obtained at the reference temperature of 298.15 K using the standard molar enthalpies of vaporization Δ l g H m ° ( T ) , the molar enthalpies of fusion, the heat capacity differences between gas and liquid and the heat capacity differences between gas and solid, Δ l g C p,m ° and Δ cr g C p,m ° , respectively, both estimated by applying a group additivity procedure. Therefore, the averages of the standard (p° = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation at 298.15 K, have been derived: