Polymorphism and thermophysical properties of l- and dl-menthol

Abstract

The thermodynamic properties, phase behavior, and kinetics of polymorphic 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 (α, β, γ, and δ forms) were observed and studied. A continuous transformation to the stable α form was detected by DSC and monitored in detail using X-ray powder diffraction. A long-term coexistence of the stable crystalline form with the liquid phase was observed. The vapor pressure measurements of both compounds were performed using two static apparatus over a temperature range from 274 K to 363 K. Condensedphase heat capacities were measured by adiabatic and Tian-Calvet calorimetry in the wide temperature interval from 5 K to 368 K. Experimental data of Land 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 a 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, the phase diagrams of L-menthol and DL-menthol were suggested.

Calculation of the Isobaric Heat Capacities of the Liquid and Solid Phase of Organic Compounds at and around 298.15 K Based on Their “True” Molecular Volume

“…Beyond these compilations a large number of recent papers presenting the heat-capacity data of several classes of compounds and of individual molecules of any kind as well as their temperature dependence have been published up to the present. Special mention shall be given to the hydrocarbons [49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65], halogenated hydrocarbons [66,67,68,69,70,71], unsubstituted and substituted alcohols and polyols including sugar derivatives [72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107], phenol derivatives [108,109], carboxylic acids […”

Directional Growth of cm-Long PLGA Nanofibers by a Simple and Fast Wet-Processing Method

“…Also known as mint camphor, (−)-menthol (or L-menthol, the most common form in nature; from now on, here referred to just as "menthol") is a chiral cyclic monoterpene alcohol, whose chemical nature allows for enhanced PLGA solubility, due to its alcoholic functional group and its alkylic frame (Figure 1c). It has four crystal polymorphs, of which the most stable one is the α phase (with a crystal habit characterized by short, broad needles) [26]. It is a waxy, crystalline substance, clear or whitish in color, solid at room temperature, with a melting point of 42-45 • C (α phase).…”

Calculation of the Vapour Pressure of Organic Molecules by Means of a Group-Additivity Method and Their Resultant Gibbs Free Energy and Entropy of Vaporization at 298.15 K

“…Further collective sources have been used to complement—and compare—the experimental data [ 8 , 14 , 15 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. In addition, vapour-pressure data have been published specifically for various saturated and unsaturated hydrocarbons [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 ], alcohols [ 53 , 54 , 55 , 56 , 57 , 58 ], phenols [ 59 , 60 ], alkyl- and arylethers [ 61 , 62 , 63 , 64 ], acetals [ 65 , 66 ], carboxylic acids [ 67 , 68 , 69 , 70 , 71 ], carboxylic halides […”