Thermochemistry of phthalic acids: Evaluation of thermochemical data with complementary experimental and computational methods

Abstract

Available from literature primary experimental results on temperature dependences of vapour pressures of phthalic, isophthalic, and terephthalic acids have been collected and they have been treated uniformly in order to derive sublimation enthalpies at the reference temperature 298.15 K. In order to evaluate the available experimental data, enthalpies of sublimation of isophthalic and terephthalic acid were obtained from the temperature dependence of vapour pressure measured by the transpiration method. Enthalpies of formation of crystalline isophthalic acid and 4-methylphthalic acid were derived by using combustion calorimetry. Gas phase enthalpies of formation of phthalic acids were calculated by the composite quantum-chemical methods G4 and G3MP2. These values were used for evaluation of experimental results and recommendation of reliable benchmark properties for thermochemical calculations. Mutual interactions of carboxylic substituents in the benzene ring were derived and discussed.