PHYSICAL PROPERTIES OF FATS AND OILS 263 



Daul)ert^^^ have shown thai litis j^lKMiomonon oV)tains with synthetic 1- 

 ni yristo-2-lauro-3- capriii . 



However, some triacid glycerides correspond with the simple triglycerides 

 in having (loul)le chain length structure. This is true when the acids vary 

 t'roni each other by 2 carbons as, for example, l-stearo-2-palmito-3-myris- 

 tin, l-palmito-2-myristo-3-laurin, and l-myristo-2-lauro-3-caprin."* On 

 the other hand, according to Lutton,'''^ the |8-forms of other triacid glycerides 

 have a triple chain length structure. Even the isomeric forms of the 

 compounds prepared by Sidhu and Daubert, namely, CisCnOie and 

 CieCiiCu, have been sho\\Ti to exist in TCL structure. 



Sidhu and Daubert"^ have reported the following constants on the tri- 

 acid glj'cerides synthesized by them: l-stearo-2-palmito-3-myristin, long 

 spacing 40.7 A., transition temperatures, 43.5-44°, 54°, and 59°C.; 1- 

 palmito-2-myristo-3-laurin, 35.7 A., 36-37°, 44°, and 48.5-49°C., respec- 

 tively, and l-myristo-2-lauro-3-caprin, 33.4 A., 22°, 33-34°, and 36.5- 

 37°C., respectively. 



e. Diglycerides. A large number of diglycerides have been prepared 

 in which the 2-acid components are the same. Two types of such di- 

 glycerides are recognized, namely, symmetrical (a, a' or 1,3-) and un- 

 symmeirical (a, /3 or 1,2-). ^Vlany of the diglycerides described in the earlier 

 literature as unsymmetrical were in reality the symmetrical isomers, due to 

 the ease in the shift of the acyl group from the 2- to the 3-position during 

 the removal of the protective grouping from the 3-position. 



In addition to those diglycerides containing a single fatty acid compo- 

 nent, considerable information has recentl}^ become available on diglycerides 

 which contain two different fatty acid components, as, for example, 1- 

 myristo-3-palmitin or l-lauro-2-stearin. In both cases (symmetrical and 

 uns\Tnmetrical diglycerides), carbon atom 2 (jS) is asymmetric, which is a 

 prerecjuisite for the existence of the diglycerides in enantiomorphic forms 

 (see discussion under optical activity of fats). 



(a) Symmetrical Diglycerides. Malkin and his co-workers*^^ have re- 

 ported thermal data and x-ray diffraction patterns on the symmetrical di- 

 glycerides from 1,3-dicaprin to 1,3-distearin. A number of such com- 

 pounds have likewise been synthesized by Averill, Roche, and King.-^ 



Griin and Theimer-" reported, as early as 1907, that s^mnmetrical diglyc- 

 erides exhibit the phenomenon of two melting points. This finding has 

 since been confirmed and extended by the demonstration that, in many 

 cases, three polymorphic forms exist. ^^-'^^ The x-ray studies seem to in- 

 dicate that the diglycerides are built up of double molecules with two acid 

 chains lying parallel on the same side of the molecule and the two free hy- 

 droxyl groups facing each other as indicated in Figure 14. 



"" T. Malkin, M. R. el Shurbagy, and M. L. Meara,./. Chew. Soc, 1937, 1409-1413. 



