Polymorphism of N-Alkanols:  1-Heptadecanol, 1-Octadecanol, 1-Nonadecanol, and 1-Eicosanol

Abstract

The polymorphism of 1-heptadecanol (C 17 H 35 OH), 1-octadecanol (C 18 H 37 OH), 1-nonadecanol (C 19 H 39 OH), and 1-eicosanol (C 20 H 41 OH) has been studied by X-ray powder diffraction, differential scanning calorimetry (DSC), Raman scattering, and infrared spectroscopy (IR). At room-temperature two monoclinic forms, and γ, are observed. For the n-alkanols with an even number of carbons the stable form is γ, whereas is the stable form for the n-alkanols with an odd number of carbons. On heating, these phases transform to a monoclinic, rotator form R' IV at a few degrees below the melting point. A metastable form is obtained by quenching from the melt for 1-octadecanol and 1-eicosanol, which is isostructural with the -phase of the odd alkanols. Cell parameters, temperatures, and enthalpies of the transitions are reported.

Melting behaviour in the n-alkanol family. Enthalpy–entropy compensation

“…An ordered form (stable at room temperature) transforms into a rotator form a few degrees below the melting point. [3][4][5][6][7] In this form the molecules have rotational disorder around their long axis. In this paper's area of concern, which is the range in which the transition from solid to liquid takes place, two different rotator forms can be stabilized.…”

“…[4][5][6] For C 17 OH, C 18 OH, C 19 OH and C 20 OH the stable form before melting is the monoclinic R 0 IV . 3,7 In energy terms the R (Fig. 1).…”

The C19H39OH–C20H41OH system: Experimental phase diagram and thermodynamic modelling

“…[10][11] At high temperature, the two constituents have the same disordered, monoclinic phase, R 0 IV (C2/m, Z ¼ 4). 9 For the preparation of mixed samples we have followed two different procedures: dissolution-evaporation (D + E), and melting-quenching (M + Q). In the case of D + E, mixed crystalline material is obtained by rapid precipitation from a solution in diethyl ether.…”

Trends and demands in the solid–liquid equilibrium of lipidic mixtures

“…Comprising multiple solid phases at the same temperature and pressure condition, literature very frequently fails to correctly describing the phase behavior of these mixtures 35 and this becomes worst as more complex behaviors are observed. What makes the SLE of fatty mixtures so particular is their inherent ability to polymorphism phenomena 4,7,37,38 . It means that the long-hydrocarbon chains of the fatty compounds and consequently their crystal lattice can be configured into numerous 40 micro-and macromolecular arrangements, directly related to the thermal treatment to which the mixture is submitted.…”

“…Since different crystal lattices are observed in these cases, namely hexagonal, orthorhombic and 50 triclinic, different transition temperatures and enthalpies are also observed. Crystalline structure of fatty acids, alcohols and esters can also pack into different polymorphic forms, usually in temperatures very close to the most stable form 9,37,39,40 . Knowing that the polymorphism phenomena can be managed by 55 particular thermal treatments, the parameters of the processes to which mixtures are submitted, time and temperature, can define the profile of the final product.…”