Combustion energies of esters (ethyl 6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carboxylate; ethyl 6-methyl-4-(4-methylphenyl)-2-oxo-1,2,3,4tetrahydropyrimidine-5-carboxylate; ethyl 4-(4-methoxyphenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5carboxylate and ethyl 4-(6-methoxyphenyl)-6-methyl-2oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate) were experimentally obtained using a bomb calorimetry. According to the experimental data, the enthalpies of combustion and the enthalpies of formation in a solid state were calculated. Derivative analysis was used to investigate the compounds within the temperature range of 483.0-577.5 K. The enthalpies of fusion, vaporization and sublimation were calculated using the results of the differential thermal analysis. According to the obtained data, the enthalpies of formation of the investigated compounds in the gaseous state were calculated. The possibility of using the Benson additive scheme to calculate the enthalpy of formation is demonstrated.

According to the temperature dependence of the solubility of 5-(2-nitrophenyl)-furan-2-carboxylic acid, 5-(3-nitrophenyl)-furan-2-carboxylic acid and 5-(4-nitrophenyl)-furan-2-carboxylic acid, in the values of enthalpy and entropy of their dissolution were calculated in ethyl acetate. Taking into account the enthalpy and entropy of melting listed up to 298 K, the enthalpies and entropies of mixing are calculated. The dependence of the solubility of carboxyl-containing substances at 298 K on their melting point was established.