Thermodynamic study of selected monoterpenes IV

Abstract

An extensive thermodynamic study of three monoterpenes, (−)-menthone, (+)-pulegone, and (−)-isopulegol, is presented in this work. Phase behaviour was investigated by a heat-flux differential scanning calorimetry (DSC) from 183 K resulting in detection of polymorphic behaviour of (−)-isopulegol and a noticeably slow crystallization of (+)-pulegone. Two static apparatus were employed for the vapour pressure measurements over a wide temperature range including environmentally important ambient temperatures. Heat capacities of liquid phase were measured by Tian-Calvet calorimetry at temperatures between 266 K and 353 K. Conformational space of the compounds was examined using the density functional theory (DFT) calculations and the ideal-gas thermodynamic properties were subsequently calculated using statistical thermodynamics. A consistent thermodynamic description was developed using the method of simultaneous correlation, where the experimental data for phase behaviour, vapour pressures, and condensed phase heat capacities and calculated ideal-gas heat capacities are treated together.