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Crystallization and transformation mechanisms of α, β‐ and γ‐polymorphs of ultra‐pure oleic acid
Author(s) -
Suzuki M.,
Ogaki T.,
Sato K.
Publication year - 1985
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/bf02541697
Subject(s) - differential scanning calorimetry , crystallization , crystallography , metastability , oleic acid , polymorphism (computer science) , melting point , materials science , stearic acid , chemistry , thermodynamics , organic chemistry , biochemistry , physics , gene , genotype
Crystallization and transformation mechanisms of ultrapure (99.999%) oleic acid were examined by Differential Scanning Calorimetry (DSC) and X‐ray diffraction. X‐ray diffraction spectra revealed three different polymorphs newly named α, β and γ, which differ from each other most significantly in the short spacing spectra. α and β were found to be equivalent to the previous data which Lutton named low and high melting polymorphs, whereas γ was newly identified in the present study. DSC studies have clarified the thermodynamic stability of the three polymorphs in a range of temperature from ‐20 to 16.2 C. β is always most stable, whereas α and γ are metastable, undergoing a reversible first‐order solid‐state transformation at ‐2.2 C (on heating). DSC also showed that the crystallization behaviors are strongly dependent on the polymorphs; α crystallizes at a much higher rate than β; despite the fact that they have close melting points (α, 13.3 C; β, 16.2 C). It was demonstrated for the first time that the above peculiar polymorphic behaviors of oleic acid are quite different from those of stearic acid, a saturated fatty acid with the same carbon chain length.