PHYSICAL, rilOPEUTlKS OF FATS AND OILS 



265 



-OH 



HO- 



Fig. 14. The molecular structure of .symmetrical diglycerides as 

 postulated by Malkin el al.^^^ 



Data on the melting points and x-ray spacings are summarized in Table 

 32. 



Baur, Jackson, Kolp, and Lutton***'- have recently made a reinvestigation 

 of the saturated 1,3-diglycerides from dilaurin through distearin. They 

 disagree with Malkin et al?^^ as to the presence of a polymorphic a-form. 



Table 33 



Long Spacings, Transition TEMPERATtTREs, and Refractive Indices of Some 



DiAciD Symmetrical Diglycerides 



Long Refractive 



spacing of Transition temperature, °C. index 



Morm, ■ / 70, 



Diglyceride A. a 0' fi ^ d' 



l-Myristo-3-caprin " 38 . 39 . 44 . 48 . — 



l-Palmito-3-laurin" 42.7 51.0 50 . 59 . 5 — 



l-Stearo-3-myristm" 47.0 50. 03.0 07.0 — 



l-Lauro-3-stearin'' — — — 02 . — 



l-Myristo-3-stearin'' — ^ — 05.5-00.5 — 



l-Palmito-3-stearin'' _ _ _ 71.0-71.5 — 



l-Lauro-3-olein'' — — — 32 .0 1 .44335 



l-Myristo-3-olem'' — — — 41.0 1.44455 



l-Palmito-S-olein* — — — 40.0 1 .44574 



l-Stearo-3-olein'' — — — 54 . 1 , 44090 



° S. S. Sidhu and B. F. Daubert, J. Am. Chem. Soc, 68, 2003-2005 (1940). 

 '' B. F. Daubert and H. E. Longenecker, J. Am. Chem. Soc, 66, 53-55 (1944). 



Judging on the basis of the strong 4.6 A. short spacings, only two varieties 

 of crystals occiu', both of which are believed to be of the l3-type. In con- 

 formity with the suggestion of Malkin these are referred to as /9-a and jS-b. 

 The long spacings for /3-b exceed those of /3-a by about 2 A. /3-a is in- 

 variably obtained from the melted diglyceride and sometimes from solvent 

 crystallization ; it is highly stable at room temperature and changes to the 

 /3-b variety only when near its melting point. The /S-b form is ther- 

 mod^'^namically the only stable type; not only is it obtained by trans- 

 formation from l3-a, but also it is the form ordinarily resulting on crystal- 

 lization from solvents. The melting points and long x-ray spacing data 

 indicate that the 1,3-diglycerides are tilted at angles of 72°12' and 66°30', 

 respectively. They exhibit spherulite structure when solidified from the 

 melted form. 



A nimiber of sjTnmetrical diglycerides composed of different acids have 



3*"- F. J. Baur, F. L. Jackscm, D. C. Kolp, and E. S. Lutton, J. Am. Chem. Soc, 71, 

 3303-3300 (1949). 



