Heat capacity and thermochemical study of trifluoroacetamide (C2H2F3NO)

The low-temperature heat capacities of trifluoroacetamide were precisely de termined with a small sample precision automated adiabatic calorimeter over the temperature range from 78 to 404 K. A solid-to-solid phase transition, a fusion and a phase transition from a liquid crystalline phase to fully l iquid phase have been observed at the temperatures of 336.911+/-0.102, 347. 622+/-0.094 and 388.896+/-0.160 K, respectively. The molar enthalpies of th ese phase transitions as well as the chemical purity of the substance were determined to be 5.576+/-0.004, 11.496+/-0.007, 1.340+/-0.005 kJ mol(-1) an d 99.30 mol%, respectively, on the basis of the heat capacity measurements. The molar entropies of the three phase transitions were calculated to be 1 6.550+/-0.012, 33.071+/-0.029 and 3.447+/-0.027 J mol(-1) K-1, respectively . Further researches of the thermochemical properties for this compound hav e been carried out by means of TG and DSC techniques. (C) 2000 Elsevier Sci ence B.V. All rights reserved.