PHVRTr AL PROPERTTI^^^ OF FATS AND OILS 273 



odes has been used by Baer and Fischer. ^-•^''''~^''- This involves the use of 

 the optical activity of d{-{-)- and Z( — )-mannitols for preparing the enantio- 

 morphs of acetoneglj^cerols. Such d(-\-)- and Z( — )-acetoneglycerols can 

 be used for preparing the corresponding a-monoglycerides by acylation ac- 

 cording to the usual procedure.^ These methods have been reviewed bj'' 

 Fischer and Baer,^*** 



b. Properties of Known Optically Active Glycerides. The specific 

 rotation and melting points of pure monoglycerides are included in Table 

 37, while these constants for some closely related compounds are given 

 in Table 38. Data on a diglyceride and several triglycerides are sum- 

 marized in Table 39. 



Table .39 

 Melting Points and Specific Rotations of Some Optically Active Di- and Tri- 

 glycerides" 



Glyceride M.p., °C. [ah Solvent 



di - )-a,/3-distearin — -2.7 CHCI3 



a-Palmityl-«',Milaurin 44 0.0 CHCI3, C5H5N 



a-Stearyl-a',/3-dipalmitin 48.5 0.0 C5H5N 



a-Lauryl-a ',/3-distearin 62 . 5 0.0 C5H5N 



a-(p Nitrobenzoyl)-a',^-distearin 67-67 .5 -1.4 CHCI3 



a-(p-Nitrobenzoyl)-a',/3-dibenzoylglycerol . . . 87-88 -19.9 (CHCl2)2 



" Adapted from H. O. L. Fischer and E. Baer, Chem. Revs., 29, 287-316 (1941). 



Fischer and Baer*^* reported a considerably higher specific rotation for 

 the a-monobutyrins (± 2.2°) than was found by Abderhalden and Eich- 

 wald^^*'^^^ ( =*= 0.84°). Similar discrepancies were noted between the values 

 for d( — )-Q;,,8-distearin obtained by the method of Griin and Limpacher^^^ 

 (0.0°) and of Fischer and Baer^^* ( — 2.7°), as well as for other compounds. 

 This would indicate the superiority of using d{-\-)- and Z( — )-acetone- 

 glycerol as starting materials rather than attempting to resolve the racemic 

 mixtures. 



The aliphatic a-monoglycerides are quite unstable and show a gradual 

 decrease in rotation.'' In fact, one-third to one-half of the original rotation 

 of crystalline monoglycerides has been shown to disappear within a year. 

 On the other hand, the aromatic a-monoglycerides are extremely stable. 

 According to Jackson and King,' no change resulted from one year's stand- 

 ing. 



The failure of the unsymmetrical mixed triglycerides to show any ob- 

 servable rotation, although they were prepared from optically active a 

 monoglycerides, is quite perplexing. Fischer and Baer^^* have suggested 



«« E. Baer and H. O. L. Fischer, J. Biol. Chem., 128, 475^89 (1939). 

 «i E. Baer and H. O. L. Fischer, J. Biol. Chem., 128, 491-500 (1939). 

 *»" H. O. L. Fischer and E. Baer, Naturmssenschaften, 25, 588-589 (1937). 



