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

Abstract

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, T m , enthalpy and entropy of fusion, Δ fus H m , Δ fus S m , 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, H T - H 298. 15 , S T - S 298. 15 and G T - G 298. 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 × 10 7 min −1 , E = 70. 64 kJ/mol, respectively.