Energetic studies of urea derivatives: Standard molar enthalpy of formation of 3,4,4′-trichlorocarbanilide

Thermochemical and thermophysical studies have been carried out for crystalline 3,4,4′-trichlorocarbanilide. The standard (p° = 0.1 MPa) molar enthalpy of formation, at T = 298.15 K, for the crystalline 3,4,4′-trichlorocarbanilide (TCC) was experimentally determined using rotating-bomb combustion calorimetry, as −(234.6 ± 8.3) kJ · mol−1. The standard enthalpy of sublimation, at the reference temperature of 298.15 K, was measured by the vacuum drop microcalorimetric technique, using a High Temperature Calvet Microcalorimeter as (182.1 ± 1.7) kJ · mol−1. These two thermochemical parameters yielded the standard molar enthalpy of formation of the studied compound, in the gaseous phase, at T = 298.15 K, as −(52.5 ± 8.5) kJ · mol−1. This parameter was also calculated by computational thermochemistry at M05-2X/6-311++G∗∗ and B3LYP/6-311++G(3df, 2p) levels, with a deviation less than 4.5 kJ · mol−1 from experimental value. Moreover, the thermophysical study was made by differential scanning calorimetry, DSC, over the temperature interval between T = 263 K and its onset fusion temperature, T = (527.5 ± 0.4) K. A solid–solid phase transition was found at T = (428 ± 1) K, with the enthalpy of transition of (6.1 ± 0.1) kJ · mol−1. The X-ray crystal structure of TCC was determined and the three-centred N–H⋯OC hydrogen bonds present analyzed.