PROPERTIES OF VITAMINS A AND RELATED COMPOUNDS 



727 



tonin ; this fact offers a satisfactory method for its separation from choles- 

 terol, Avhich can be quantitatively precipitated as the digitonide. 



(2) Distillation 



Heilbron et al."" and Carr and JewelP^ state that vitamin A alcohol dis- 

 tills at 136-137°C. at a pressure of 10~' mm. However, Hickman"*'"^ 

 reported the distillation temperature as 120-125°C. under 5 X 10~^ mm. 

 pressure. On the other hand, the natural vitamin A esters distill at much 

 higher temperatures, i.e., 200-240°C. under 10"'' mm. Distillation thus 

 offers a simple method for the separation of the esters from the free vita- 

 min A alcohol. Hickman^^' notes the following temperatures as elimina- 

 tion maxima (in °C.) for various free and esterified natural and synthetic 



I60°C 



Fig. 5. The comparative elimination curves of anliydrovitamin A (- -) 

 and vitamin A alcohol ( — ) when subjected to molecular distillation.^^' 



vitamin A preparations: crystalline vitamin A alcohol, 123; saponified 

 fish liver oil, commercial concentrates, 123; crystalline vitamin A acetate, 

 132; crystalline vitamin A palmitate, 208; halibut liver oil, 212; U.S.P. 

 Keference Oil II, 214; and distilled vitamin A esters, commercial concen- 

 trates, 214. A typical elimination curve for vitamin A alcohol is given in 

 Figure 5. 



The separation of the vitamin A bj^ distillation of an unsaponified fish 

 liver oil is illustrated in Figure 6. By the passage of the oil through the 

 molecular still with carefully controlled rates of distillation, it is possible to 

 concentrate the vitamin A esters into a single distillate, while the undesir- 

 able acids and odors are separated in a lighter fraction. The bulk of the 

 esters of the other non-saponifiable factors and the parent oil are left undis- 

 tilled and substantially unchanged. 



"1 K. C. D. Hickman, Chem. Revs., 34, 51-106 (1944). . 



