Polymorphism of linoleic acid (cis-9, cis-12-Octadecadienoic acid) and alpha-linolenic acid (cis-9, cis-12, cis-15-Octadecatrienoic acid)

摘要

Crystallization and polymorphic properties of linoleic acid (cis-9, cis-12-Octadecadienoic acid) (LA) and alpha -linolenic acid (cis-9, cis-12, cis-15-Octadecatrienoic acid) (alpha -LNA) have been studied by optical microscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The DSC analyses presented three polymorphs in LA, and two polymorphs in alpha -LNA. The XRD patterns of the higher- and lower-temperature forms in LA and alpha -LNA showed orthorhombic O'(parallel to) + O-like and O'(parallel to) subcell, which were similar to those of alpha- and gamma -forms of mono-unsaturated fatty acids, respectively. From the solvent crystallization of LA and alpha -LNA in acetonitrile, single crystals of the higher temperature polymorphs have been obtained. The crystal habits of truncated rhombic shape were also similar to those of alpha -forms of the mono-unsaturated fatty acids. The enthalpy and entropy values of fusion and dissolution of the alpha -forms of LA, alpha -LNA and oleic acid showed that the two values decreased with increasing number of the cis-double bond. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved. [References: 37]