Polymorphism and thermophysical properties of L- and DL-menthol
Vojtech Stejfa, Ala Bazyleva, Michal Fulem, Jan Rohlicek, Eliska Skorepova, Kvetoslav Ruzicka, Andrey V. Blokhin
The thermodynamic properties, phase behavior, and kinetics of polymorph transformations of racemic (DL-) and enantiopure (L-) menthol were studied using a combination of advanced experimental techniques, including static vapor pressure measurements, adiabatic calorimetry, Tian-Calvet calorimetry, differential scanning calorimetry (DSC), and variable-temperature X- ray powder diffraction. Several concomitant polymorphs (alpha, beta, gamma, and delta forms) were observed and studied. A continuous transformation to the stable alpha-form was detected by DSC and in detail monitored using the X-ray powder diffraction. A long-term coexistence of the stable crystalline form with liquid phase was observed. The vapor pressure measurements of both compounds were performed using two static apparatus over a temperature range from 274 to 363 K. Condensed-phase heat capacities were measured by adiabatic and Tian-Calvet calorimetry in the wide temperature interval from 5 to 368 K. Experimental data of L- and DL-menthol are compared mutually as well as with available literature results. The thermodynamic functions of crystalline and liquid L-menthol between 0 K and 370 K were calculated from the calorimetric results. The thermodynamic properties in the ideal-gas state were obtained by combining statistical thermodynamics and quantum chemical calculations based on thorough conformational analysis. Calculated ideal-gas heat capacities and experimental data on vapor pressure and condensed-phase heat capacity were treated simultaneously to obtain a consistent thermodynamic description. Based on the obtained results, phase diagrams of L-menthol and DL-menthol were suggested.
, Bazyleva, A.
, Fulem, M.
, Rohlicek, J.
, Skorepova, E.
, Ruzicka, K.
and Blokhin, A.
Polymorphism and thermophysical properties of L- and DL-menthol, Journal of Chemical Thermodynamics, [online], https://doi.org/10.1016/j.jct.2018.11.004, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=926687
(Accessed November 29, 2023)