Determination of Heat Capacities and Thermodynamic Properties of 2-(Chloromethylthio)benzothiazole by an Adiabatic Calorimeter

Abstract

The molar heat capacities of 2-(chloromethylthio)benzothiazole (molecular formula C8H6ClNS2, CA registry no. 28908-00-1) were measured with an adiabatic calorimeter in the temperature range between (80 and 350) K. The construction and procedures of the calorimeter were described in detail. The performance of the calorimetric apparatus was evaluated by heat capacity measurements on α-Al2O3. The deviation of experiment heat capacities from the corresponding smoothed values lies within ±0.3%, whereas the uncertainty is within ±0.5%, compared with that of the recommended reference data over the whole experimental temperature range. A fusion transition was found from the Cp−T curve of 2-(chloromethylthio)benzothiazole. The melting temperature and the molar enthalpy and entropy of fusion of the compound were determined to be Tm = (315.11 ± 0.04) K, ΔfusHm = (17.02 ± 0.03) kJ·mol-1, and ΔfusSm = (54.04 ± 0.05) J·mol-1·K-1, respectively. The thermodynamic functions (HT − H298.15) and (ST − S298.15) were also derived from the heat capacity data. The molar fraction purity of the 2-(chloromethylthio)benzothiazole sample used in the present calorimetric study was determined to be 99.21 by fraction melting.