Experimental and computational thermodynamic study of ortho- meta- and para-aminobenzamide

The vapour pressures of the three crystalline isomers of aminobenzamide were measured using the Knudsen mass-loss effusion technique. From the temperature dependence of the vapour pressures, the standard (p° = 0.1 MPa) molar enthalpies, Gibbs energies and entropies of sublimation, at T = 298.15 K, were derived. The standard molar enthalpies of formation of the three isomeric aminobenzamides in the crystalline phase, at T = 298.15 K, were determined from static bomb calorimetric experiments. These values were combined with the results of standard molar enthalpies of sublimation to derive the standard molar enthalpy of formation in gaseous phase, at T = 298.15 K, of ortho-aminobenzamide, −(113.1 ± 1.5) kJ·mol−1, meta-aminobenzamide, −(98.9 ± 1.6) kJ·mol−1, and para-aminobenzamide, −(100.3 ± 1.6) kJ·mol−1. The temperature and molar enthalpy of fusion of the studied compounds were measured using differential scanning calorimetry. Additionally, very high-level quantum-chemical calculations at the composite G3 level have been conducted in an attempt to accurately describing the energetic of all isomers. The experimentally observed enthalpies of formation have been fully corroborated by the very accurate calculations.

► Vapour pressures of the three crystalline aminobenzamides were measured.
► Enthalpies, entropies and Gibbs energies of sublimation were derived.
► Enthalpy and Gibbs energy of formation in the crystal and gas phases were calculated.
► Gas phase enthalpy of formation was also estimated by quantum chemical calculations.