The Binary System Tetradecanedioic Acid–Hexadecanedioic Acid: Polymorphism of the Components and Experimental Phase Diagram

Abstract

Complementary techniques had to be applied to investigate the binary system tetradecanedioic acid (C 14 H 26 O 4 )-hexadecanedioic acid (C 16 H 30 O 4 ), because all the forms observed have the same space group (P2 1 /c; Z = 2). We studied the polymorphism of the two single compounds and of their mixtures by X-ray powder diffraction, differential-scanning calorimetry (DSC), infrared spectroscopy (IR), scanning electron microscopy (SEM), and thermo-optical microscopy (TOM). The two diacids were found to be isopolymorphic. At low temperature, they crystallize in the same ordered C-form, and, on heating, adopt the ordered C h -form, 18 below their melting point. In contrast to similar compounds (unbranched alkanes, alkanols, and fatty acids), the solid-solid and solid-liquid phase-transition temperatures decrease with increasing chain length. At low temperature, a new monoclinic form, C i , appears as a result of the disorder of composition in the mixed samples. There are two [C + C i ]-type solid-solid domains. On heating, the solid domains are related to solid-liquid domains by a peritectic invariant for compositions rich in C 14 H 26 O 4 , and by a eutectic invariant for compositions rich in C 16 H 30 O 4 . At higher temperature, there appears a second peritectic invariant for compositions rich in C 14 H 26 O 4 , together with a metatectic invariant for compositions rich in C 16 H 30 O 4 . All the solid forms observed in this binary system are isostructural. Nevertheless, the equilibrium between them is complex near the melting point, and their miscibility in the solid state is reduced.

Binary solid–liquid equilibrium systems containing fatty acids, fatty alcohols and triolein by differential scanning calorimetry

“…Lauric acid and myristic acid present light inflection thermal event also observed by Maximo et al and Costa et al [25,27]. As reported by Ventolà et al [35], this light inflection suggests the presence of a solid-solid transition overlapping the solid-liquid phenomena highlighted by black arrow (see inserts in Fig. 1).…”

“…In the same figure, it is possible to observe that fatty alcohols (1-decanol, 1-dodecanol and 1-tetradecanol) also exhibit overlapped peaks and triolein showed two well-defined peaks in the temperature range studied. According to literature by Ventolà et al [35], the presence of overlapped peaks can indicate that polymorphic transitions probably occurred during the melting processes of these fatty compounds; thus, determining the transition enthalpy by means of peak area measurement does not lead to accurate and reliable values [27]. [27] 311.39 [27] 47.60 [27] a Uncertainty of melting temperature and molar enthalpy of fusion AE 0.30 K and AE 0.037 kJ mol À1 , respectively.…”

Solid-liquid equilibrium of binary and ternary systems formed by ethyl laurate, ethyl palmitate and dodecylcylohexane: Experimental data and thermodynamic modeling

“…[11e13]. Ventol a et al [26] analyzed similar compounds and suggested that the inflection points observed in the melting peak are due to the presence of solidesolid transitions overlapping the solideliquid transition. According to Leitão et al [27], these transitions can be ascribed to the transition between single crystalline forms, mixtures of several polymorphic forms or amorphous states.…”

Two-Dimensional Order in Mercury-Supported Langmuir Films of Fatty Diacids

“…This planar alignment of the molecules promotes molecular self-organization into structures dominated by the lateral interactions of their various moieties, in particular the HBs between the molecules’ craboxyl end groups. However, as for all 2D structures, the X-ray GID patterns presented above, although having considerably more peaks than those of most liquid-supported interfacial layers, ,,, have still much fewer peaks than the diffraction patterns of 3D single crystals or powders of the same compounds, which may contain hundreds to thousands of lines. ,− Thus, the elucidation of fine details in the headgroup and the chain ordering from our GID patterns is more prone to ambiguities and uncertainties. Using additional information from relevant 2D or 3D system can, however, enhance considerably the confidence and validity of the extracted structure.…”