PHYSICAL PROPERTIES OF FATS AND OILS 257 



were reported b}^ -Malkin and Meara^'*-'^ to exist in four modifications. 

 In each group, the rate of transition of the different crystal forms de- 

 creases with increasing chain length. In the presence of the shorter chain 

 acids, a linear relation between the chain length and the long spacings 

 usually cannot be observed for the a- or /3'-forms. In the case of the /3- 

 members, the long spacings usually correspond to two molecular lengths. 

 Strangely enough, palmitodilaurin and stearodimyristin possess a much 

 shorter long spacing. Malkin and Meara^^"*-^^* attribute this discrepancy 

 to an acute angle tilt of 41° 18'. 



Data on the melting points, the long spacings, and the refractive indices 

 are summarized in Table 28. 



2-Caproyldi stearin and 2-caprylyldistearin have likewise been studied 

 and shown to melt at 47.2° and 51.8°C., respectively.^" The refractive 

 indices for these two compoinids are reported as 1.44019 and 1.44140, re- 

 spectively, at 70°C. 



Daubert and his co-workers have sjaithesized a series of 2-oleo-l,3-diacyl 

 glycerides"^ which were showii to have the following melting points: 

 dicapryl, 5-6°C.; dilauryl, 14.5-15°C.; dimyristyl, 26-27°C.; dipal- 

 mityl, 35.5-36°C.; and distearyl, 42.5-43°C. The usual four poly- 

 morphic forms were reported by Daubert and Clarke, ^^^ and their trans- 

 formation temperatures were determined. The 2-oleo compounds showed 

 crystal spacings approximately three times the length of the longer 

 g^(.j(^ 92,369,3-0,375 ^\i{s fact precludcs the tuning fork arrangement originally 

 noted with the completely saturated symmetrical triglycerides and the 

 simple triglycerides. 2-Oleodistearin, isolated from kokum butter, has 

 been shown to be identical with the synthetic product of Filer et al. ^™ as re- 

 gards both the thermal and the x-ray data on the 3-polymorphic forms. 

 Lutton^«3 reported melting points of 22.4, 36.2, and 44.3°C. for the a, x-3, 

 and /33 forms. The intermediate compound possesses a pattern not 

 hitherto encountered. 



The symmetrical triglycerides can be assumed to have a modified tuning 

 fork arrangement. The projected and tilt forms of this structure for the 

 double chain length structures is sho^^^l in Figure 10 and for the triple chain 

 length structures in Figure 11. A special case of the TCL structure as ap- 

 plied to symmetrical oleodistearin is given in Figure 12. A new "chair" 

 arrangement for unsymmetrical diacid triglycerides recently proposed by' 

 Lutton^'^ is pictured in Figure 13. 



In several instances, the /3'-forms of the symmetrical mixed triglycerides 

 of C„C„_4C„, C„C„_6C„ and mixed Cio-Cg, w^ere shown to have long x-ray 



^^ F. L. Jackson, B. F. Daubert, C. G. King, and H. E. Longenecker, J. Arn. Chem. 

 Soc, 66, 289-290 (1944). 



^' B. F. Daubert and T. H. Clarke, ./. .4 m. Chem. Soc, 66, 690-691 (1944). 

 =>'* S. S. Sidhu and B. F. Daul)ert, J. Am. Chem. Soc, 69, 1451-1453 (1947). 



