Thermodynamic study of phthalic, isophthalic, and terephthalic acids

A thermodynamic study of phthalic, isophthalic, and terephthalic acids (gen eral formula: C8H6O4) was carried out by sublimation calorimetry and differ ential thermal analysis. With values of combustion enthalpy taken from the literature, it was possible to determine their enthalpies of formation in t he gaseous state and at 298.15 K and their resonance energy. The results en abled us to do a comparative study of the relative stability of the three a cids, on the one hand, and of different benzene disubstituted derivatives, on the other hand. From the enthalpy of sublimation, it was possible to det ermine the energetic contribution of the different intermolecular forces in the crystals of the three acids.