Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

The standard (p = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, of the cyclic anhydrides of glycine and DL-alanine, at T = 298.15 K, were derived from the standard molar energies of combustion in oxygen, measured by static bomb combustion calorimetry. For these compounds, the standard molar enthalpies of sublimation, at T = 298.15 K, were determined from the temperature-vapour pressure dependence, obtained by the Knudsen mass-loss effusion method. Through the values for the heat capacity differences between the gas and the crystalline phases of the studied compounds, the standard (p o = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, were derived. From the experimental values, the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of glycine anhydride and DL-alanine anhydride were calculated as (321.0 +- 1.9) kJ mol 1 and (382.7 +- 2.0) kJ mol 1 , respectively. A theoretical study at the G3 and G4 levels has been carried out, and the calculated enthalpies of formation have been compared with the experimental values.