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 ΔlgHm°(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 ΔcrgHm°(298.15 K) were obtained at the reference temperature of 298.15 K using the standard molar enthalpies of vaporization ΔlgHm°(T), the molar enthalpies of fusion, the heat capacity differences between gas and liquid and the heat capacity differences between gas and solid, ΔlgCp,m° and ΔcrgCp,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:CompoundΔcrgHm°(298.15 K) (kJ mol−1)ΔcrgSm°(298.15 K) (J mol−1 K−1)ΔcrgGm°(298.15 K) (kJ mol−1)4-Ethoxyacetanilide120 ± 3232 ± 952 ± 54-Hydroxyacetanilide138 ± 3245 ± 965 ± 54-Bromoacetanilide110 ± 4204 ± 1049 ± 6Full-size tableTable optionsView in workspaceDownload as CSV