Thermodynamic Properties of Trifluoromethanethiol from 12°K to Its Boiling Point. Entropy from Molecular and Spectroscopic Data

The heat capacity of trifluoromethanethiol has been measured from 12° to 227°K. The heat of fusion at the triple point temperature, 116.04°K, was 1177 cal mole^—1. The heat of vaporization at the normal boiling point, 235.16°K, was 4798 cal mole^—1. The vapor pressure has been measured, and the data are represented by the equation ${\log }_{10}{p}_{\mathrm{mm}}\text{=(−1352.568/T)−2.686918}{\log }_{10}\text{T+15.00409}$ . The entropy of trifluoromethanethiol gas calculated from the calorimetric data was 69.45±0.17 eu at 235.16°K. The result calculated from spectroscopic data and structural parameters for the molecule was 70.19 eu. The discrepancy of 0.74±0.17 eu has been attributed to a potential barrier of 1540±260 cal mole^—1 restricting the internal rotation of the trifluoromethyl group.