PHYSICAL PROPERTIES OF FATS AXD OILS 259 



recent work report .s a maximum of three polymorphic forms instead of the 

 four noted earher. The glassy or 7-pol3'morph has not been found. 

 The symmetrical isomers showed a high degree of crystallinity, while the 

 unsymmetrical forms were microcrystalline. The a-forms were the lowest 

 niching in all cases; this polymorph was unusually stable in the case of 2- 

 palmitodistcarin and quite labile in the case of 2-stearodipalmitin. PSP 

 gave rise to the 0'- but not to the )3-form, while SPS was found only as the 

 /^-polymorph. In the case of 1-palmitodistearin, only the /S'-form obtained 

 from the melt and the |S-type from the solvent; both were equally stable. 

 The results on 1-stearodipalmitin were normal and both the /3'- and the /S- 

 crystals were stable. The melting points for a given form of triglyceride 

 were shown to vary by several degrees, depending upon the degree of 

 stabilization. Table 29 summarizes the data on the long spacing. 



Table 29 

 Long Spacixgs (Angstrom Unit.s) of Mixed TRiGLYCEmDEs Containing Palmitic 



AND Stearic Acids 



Data of Lutton et al."- Data of Carter and Malkin*''' 



Triglyceride a /S' /J a /3' /? 



2-Palmito-l,3-distearin 49.2 — 43.1 50.5 47.5 44.2 



2-Stearo-l,3-dipalmitin 46.65 42.75 — 50.2 44.7 43.2 



l-Palmito-2,3-disteann 48.5 45.1 44.7 48.8 44.7 46.5 



l-Stearo-2,3-dipalmitin 47.6 43.8 42.1 47.8 43.9 42.5 



" E. S. Lutton, F. L. Jackson, and O. T. Quimby, J. Am. Chem. Soc, 70, 2441-2445 

 (1948). 

 * T. Malkin and M. L. Meara, /. Chem. Soc, 1939, 103-108. 

 ' M. G. R. Carter and T. Malkin, ./. Chem. Soc, 1939, 577-581. 



Lutton,*'^ in a recent study of saturated diacid triglycerides, has dem- 

 onstrated that the a-forms, in all cases, and the /3'-forms had the double 

 chain length structure (DCL). On the other hand, where one of the acids 

 was four or more carbons shorter than the second acid component, a triple 

 length structure (TCL) was invariably found for the /3-polymorph. This 

 phenomenon was reported for the following saturated mixed triglycerides: 

 C„C„_4C„; C„C„_6C„; C„_6C„C„_6; and mixed do-Cg. It is also 

 probable that the TCL is the form for C„_4C„C„_4. 



c. Unsymmetrical Mixed Triglycerides. A large number of the 1-acyl- 

 2,3-diglycerides have been synthesized by Carter and Malkin. ^"^-^^^ This 

 .series of triglycerides was sho^\Tl to exist in the usual four common poly- 

 morphic forms. The transition from one type of poljnnorph to another 

 proceeds more sluggishly than is the case with their counterparts in the 

 symmetrical mixed triglyceride series. The change from /3' to /S takes place 

 quite slowly. The melthig points of the unsymmetrical mixed triglycerides 

 are in general slightly lower than those of their svTnmetrical isomers. The 



