Optically Active and Racemic Glycerides. II. Thermodynamic Studies on the Polymorphic Transition of (R)- and (RS)-1,2-Diglycerides

• Published in: Bulletin of the Chemical Society of Japan Vol. 57; no. 4; pp. 956 - 959
• Main Authors: Iwahashi, Makio, Ashizawa, Kazuhide, Ashizawa, Miyuki, Kaneko, Yoshihide, Muramatsu, Mitsuo
• Format: Journal Article
• Language: English
• Published: Tokyo The Chemical Society of Japan 01.04.1984; Chemical Society of Japan
• ISSN: 0009-2673; 1348-0634
• DOI: 10.1246/bcsj.57.956

The polymorphic relationship between optically active (R)- and for racemic (RS)-forms of 1,2-distearin and 1,2-dipalmitin were studied by X-ray diffraction, infrared spectrum, and the thermal analysis. These glycerides have two crystalline forms, α and β, wherein α is metastable and β is stable under ordinary conditions. The α→β transformation for the (RS)-1,2-distearin crystal was extremely slow as compared with that for the (R)-form crystal, implying that the β-form crystal of (RS)-1,2-distearin is an eutectic mixture of small (R)- and (S)-crystals while the α-form crystal of (RS)-1,2-distearin is composed of a replacement type solid solution of (R)- and (S)-1,2-distearin molecules. Almost the same results were obtained with 1,2-dipalmitin, for which the rate of α→β transformation is higher than that for the 1,2-distarin, probably because of a higher mobility of this compound.