Heat Capacities and Thermodynamic Properties of 3-(2,2-Dichloroethenyl)-2,2-dimethylcyclopropanecarboxylic Acid

The heat capacities of 3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylic acid(a racemic mixture, molar ratio of cis-/trans-structure is 35/65) in a temperature range from 78 to 389 K were measured with a precise automatic adiabatic calorimeter. The sample was prepared with a purity of 98. 75% (molar fraction). A solid-liquid fusion phase transition was observed in the experimental temperature range. The melting point, Tm, enthalpy and entropy of fusion, ΔfusHm, ΔfusSm, of the acid were determined to be (331. 48 ± 0. 03) K, (16. 321 ± 0. 031) kJ/mol, and (49. 24 ± 0. 19) J/(K · mol), respectively. The thermodynamic functions of the sample, HT - H298. 15, ST - S298. 15 and GT - G298. 15, were reported at a temperature intervals of 5 K. The thermal decomposition of the sample was studied using thermogravimetric(TG) analytic technique, the thermal decomposition starts at ca. 418 K and ends at ca. 544 K, the maximum decomposition rate was obtained at 510 K. The order of reaction, preexponential factor and activation energy are n = 0. 23, A = 7. 3 × 107 min−1, E = 70. 64 kJ/mol, respectively.