PHYSICAL PROPERTIES OF FATS AND OILS 269 



2-palmityl glycerol. The same procedure was employed later by Stimmel 

 and Kiiig^*^ for the preparation of a number of other symmetrical diglyc- 

 erides. Daubert^^ synthesized 2-monobutyrin, which boils at 140-141 °C. 

 at 4 mm. Hg. 



Although the /j-monoglycerides do not rearrange to produce the a-ester 

 on melting, such a shift takes place readily when hydrogen or hydroxyl 

 ions aie present as catalytic agents. King and associates^- ^^ have re- 

 l)oited that /i-monopalmitin completel}' changes to the a-isomer within 24 

 hours when it stands in an alcoholic solution containing 0.05 A^ hydrochloric 

 acid or 0.1 A" ammonium hydroxide. The aromatic monoglycerides are 

 distinctly more stable than are the related aliphatic esters. 



The melting points of the 1-monoglycerides are consistently higher 

 than those of the 2-monoglycerides. The latter compounds are more 

 soluble in organic solvents than are the 1-monoglycerides. Thus, sym- 

 metrical monopalmitin dissolves in alcohol at 25°C. to the extent of 4.61 

 g. per 100 ml., compared with a value of 4.09 g. for the unsymmetrical 

 compound. The difference in ether is much greater, however, being 

 11.15 and 2.75 g. per 100 ml., respectively, for the two types of mono- 

 palmitin.^ 



Although no thermal data are available on the polymorphic forms of 2- 

 monoglycerides, the results from x-ray diffraction studies indicate that the 

 glycerol residues are similarly oriented in the two forms. ^'^^ However, the 

 angle of tilt of the jS-form is greater in the 1-monoglyceride than in the 2- 

 monoglyceride, being 58°41' and 45° 19', respectively. This produces a 

 difference in long spacing corresponding to that of 2 carbons. The data on 

 melting point and refractive indices for the 2-monoglycerides are sum- 

 marized in Table 35. 



(2) Soluhility 



Most of the glycerides are soluble in all of the so-called "fat solvents." 

 These include petroleum ether, hexane, diethyl ether, chloroform, benzene, 

 ethanol (hot), acetone, carbon disulfide, ligroin, gasoline, cyclohexane, 

 carbon tetrachloride, and other similar solvents. None of the glycerides is 

 soluble in water. 



The unsymmetrical mixed triglycerides are more soluble than are the 

 corresponding symmetrical compounds. Thus the following variations 

 have been report ed^^-^^^'^^^ in the solubility of the unsymmetrical acyl 

 dilaurhis and of the symmetrical acyl dilaurins expressed in g./lOO ml. in 

 ethanol at 25°C.: caprylyl, 16.31 and 14.34; capryl, 9.00 and 3.02; my- 

 ristyl, 1.21 and 0.25; and palmityl, 0.54 and 0.38. Similar discrepancies 

 in solul)ility of acyl dislearins have been reported. Thus, a-acyl (uns^mn- 



'»» L. J. Filer, S. S. Sidhu, B. F. Daubert, and H. E. Longenecker, J. Am. Chem. Soc, 

 66, i:«3-1337 (19-1-1). 



