260 HI. CHEMISTRY OF NEUTRAL FATS 



long crystal spacings and the side spacings of the /3-form as demonstrated 

 by the x-ray diffraction patterns show close similarity, in most cases, to 

 those of the simple triglycerides. A summary of the data on melting points, 

 long spacings, and refractive indices is included in Table 30. 



As is the case with the symmetrical diacid triglycerides, all the a- and 

 /3'-modifications (with one possible exception) have the double chain length 

 structure. However, the triple chain length pattern obtains in a number of 

 the /3-compoimds where the chain lengths of the 2-acid components differ 

 by 4 or more carbon atoms. These include C„C„_4C„_4, C„_6C„C„, and 



Daubert, Fricke, and Longenecker*" have succeeded in overcoming the 

 difficulties inherent in the synthesis of unsymmetrical mixed triglycerides 

 with an unsaturated acid component. The monooleoglycerides were 

 found to have melting points approximately 35° C. lower than the corre- 

 sponding saturated compounds; the l-elaido-2,3-diacyl glycerides melt 

 approximately 15° higher than the corresponding oleo compounds, but 20° 

 lower than the stearo derivatives. Some of the data on these are sum- 

 marized in Table 31. 



The introduction of a linoleic acid residue in place of the oleo group 

 brings about a further lowering in melting points of the several derivatives. 

 The series of l-acyl-2,3-dioleins studied possessed somewhat lower melting 

 points than the 1-oleo derivatives, while the dilinolein series was found to 

 have the lowest melting points of any of the samples investigated. 



d. Triacid Triglycerides. A considerable number of triglycerides con- 

 taining three separate acids are known to occur naturally. An extensive 

 series has also recently been synthesized by Chen and Daubert, ^^* using a 

 reaction first described by Verkade and van der Lee^^ in which a 1-mono- 

 glyceride is first converted to l-acyl-3-tritylglycerol. A second different 

 acid residue can be placed in the /3-position; on hydrolysis, a 1,3-diglyceride 

 results, into which a third acid can then be introduced into position 2. 

 If the trityl group is removed from the l,2-diacyl-3-tritylglycerol by hy- 

 drogenolysis, the 1,2-diglyceride results, instead of the 1,3-isomer, and 

 the third acid residue can then be directed into position S."^-^*" 



The triacid glycerides exist in the usual three forms {a, /3', /3). In some 

 cases, the iS '-variety with the intermediate melting point has been shown 

 to have the greatest stability. Frequently, the /3'-form results on crys- 

 tallization of the triglyceride from solvents, instead of the /3-variety of 

 crystals which are usually formed under such circumstances. Sidhu and 



"■f B. F. Daubert, H. H. Fricke, and H. E. Longenecker, /. Am. Chem. Soc, 65, 2142- 

 2144 (1943). 



"8 C. Chen and B. F. Daubert, /. Am. Chem. Soc, 67, 1256-1258 (1945). 



3'9 P. E. Verkade, F. D. Tollenaar, and T. A. P. Posthumus, Rec. trav. chim., 61, 373- 

 382(1942); Chem. Zentr., 1942, 11, m^. 



380 P. Verkade, Rec. trav. chim., 62, 393-397 (1943). 



