Polymorphic behavior of erucic acid

Polymorphic behavior of erucic acid was examined by differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and optical microscopy. Four individual polymorphs were observed, α1, γ1, α and γ. The single crystals of α and α1 were obtained from acetonitrile solutions. DSC and XRD studies exhibited reversible transformations between α and γ, and between α1 and γ1. The two transformations were characterized by an order (γ and γ1)-disorder (α and α1) transformation due to melting of the aliphatic chain between acis double bond and a methyl end group, as revealed in α and γ of oleic acid. The thermodynamic stability among the four polymorphs was determined based on the transformation features and the solubility data. α1 is most stable above 25.9 C, melting at 34.0 C, α is most stable in a range of temperature between −1.0 and 25.9 C, transforming in a crystalline state to α1 at 31.2 C on heating. γ is most stable below −1.0 C. It can be concluded that the polymorphism of erucic acid is different from that of oleic acid with respect to the thermal and structural behaviors, although some similarities are revealed.