170 III. CHEMISTRY OF NEUTRAL FATS 



HsCOCfcsHs), HzCOCtesHs), H2COH 



HCOH "-^^^ ► HCOOCR ""'''' ► HCOOCR 



HsCOClCsH,), H2COC(C6H5)3 H2COH 



1,3-Ditrityl 2-Afyl-l,3- /3-Mouoglyceride 



glycerol glycerol 



The earlier method of Griin-" for preparing the /3-monoglyceride, which 

 involves treating 1,3-dichlorohydriD with an acyl chloride and subse- 

 ciuently removing the chlorine, has been shown by Fairbourne-'--" to be 

 unreliable. Similarly, the acid hydrolysis of /S-acylditritylglycerols re- 

 sults in the a- rather than in the expected /3-monoglyceride.'' 



Eckey and Formo-^ have recently described a method involving directed 

 interesterification for the production of monoglycerides. When cottonseed 

 oil was mixed with an excess of glycerol, and sodium methoxide in xylene 

 was used as the catalyst, a considerable amount of monoglyceride resulted. 

 When the reaction was allowed to continue for 3 days at 26.7°C., 27% of the 

 fat was separated as the crystalline monoglyceride. When the latter 

 product was purified b}^ recrystallization from petroleum ether at 4.4°C., 

 it was shown to be relatively pure. 



(2) Diglycerides 



Two types of diglycerides are known, namely the symmetrical or a,a'- 

 compound, and the unsymmetrical or a:,/3-isomer. A further differentia- 

 tion involves the classification of those diglycerides into the simple di- 

 glycerides (where the two fatty acid residues are the same) and the mixed 

 diglycerides (in which two different fatty acid molecules are involved). 



a. Symmetrical Diglycerides. The method of Fischer, Bergmann, and 

 Barwind^ has been quite widely used for the synthesis of the diglycerides 

 of the a:,Q: '-type. This involves a reaction between alival (a-iodohydrin) 

 and the acyl chloride. 



HsCOOCR 



4AgI+HN03 



1,2-Diacyl- 1 ,3-Diglyceride 



iodohydrin 



A similar reaction for the preparation of symmetrical diglycerides em- 

 ploys trityl.'^'-^'^* After hydrolysis of l-trityl-2,3-diacylglycerol with hy- 

 drobromic acid in chloroform, the symmetrical rather than the unsym- 

 metrical diglyceride is the final product. 



20 A. Griin and E. Theimer, Ber., J^O, 1792-1801 (1907). 



21 A. Fairbourne and G. E. Foster, /. Chem. Soc, 127, 2759-2764 (1925). 

 " A. Fairbourne and G. E. Foster, /. Chem. Soc, 129, 3146-3151 (1926). 



" E. W. Eckey and M. W. Formo, J. Am. Oil Chemists' Soc, 26, 207-211 (1949). 

 " P. E. Verkade and J. van der Lee, Rec trav. chim., 55, 267-277 (1936). 



