Calorimetric studies on two halogenated uracil isomers

The heat capacities of 6-chlorouracil and 5-chlorouracil isomers were measured using a Quantum Design physical properties measurement system (PPMS) based on a heat pulse relaxation method over the temperature range from (1.9 to 300) K, and the experimental data were fitted as a function of temperature using a series of theoretical and empirical models for the appropriate temperature ranges. The results of these fits were used to calculate thermodynamic function values, Cp,m0, △0TSmo, and △0THmo from T = (0.5 to 300) K. The standard molar heat capacities, entropies and enthalpies of 6-chlorouracil and 5-chlorouracil at 298.15 K and 0.1 MPa were determined to be Cp,mo = (136.94 ± 1.37) J K−1 mol−1 and (137.95 ± 1.38) J K−1 mol−1, Smo = (156.87 ± 1.57) J K−1 mol−1 and (154.97 ± 1.55) J K−1 mol−1 and Hmo = (23.01 ± 0.23) kJ mol−1 and (23.07 ± 0.23) kJ mol−1, respectively.