28 



VITAMINS A AND CAROTENES 



TABLE IX— Continued 



Common and scientific name 



Source 

 of oil 



Oil content, 

 % 



Vitamin A, I.U./g. oil 



Black rockfish (Scorpaenidae sp.) 



Red rockfish (Scorpaenidae sp.) 

 Swordfish (Xiphias gladius) 

 Ishnagi (Stereolepis ishnagi) 

 Pacific mackerel (Decapturus sp.) 

 Pacific halibut (Hippoglossus steno- 



lepis) 

 Stonebass (Polyprion americanus) 

 Ling cod (Ophiodon elongatus) 

 California jewfish (Stereolepis gigas) 



h. Isolation 



The technique used for the isolation of vitamin A does not differ ap- 

 preciably from that used for the isolation of the provitamins A. Vitamin 

 A is quite frequently found in liver oils in the form of its esters^" and some- 

 times is found bound to a protein moleculeJ^ It is therefore necessary to 

 saponify the liver oils under specified conditions in order to isolate the vi- 

 tamin in the pure state. Furthermore, it is advisable to use an oil of very 

 high potency or to concentrate low-potency oils by molecular distillation.^^ 

 The concentrate is then heated for about one-half hour at 60 to 70° with 

 3 to 4 volumes of 10 % alcoholic potassium hydroxide while passing a stream 

 of pure nitrogen through the mixture. Finally, the mixture is cooled and 

 diluted with about ten times its volume of deoxygenated water and ex- 

 tracted with reagent-grade ethyl ether. The ether extract is then washed 

 once with 10 % salt solution, with water, and dried. The ether is then re- 

 moved under reduced pressure and the vitamin A concentrate further puri- 

 fied either by low temperature fractionation from methanoP- ■ ^^ or by mo- 

 lecular distillation and subsequent recrystallization at low temperatures 

 from ethyl formate. ^^ The first method yields a product in the form of yellow 

 needles, m.p. 7.5 to 8°, and contains methanol of crystallization;^^ the 

 second method produces a product in yellow prisms free from solvent, 

 m.p. 63 to 64°. 



c. Physical and Chemical Properties 



The crystals of vitamin Ai are isotropic and are fairly stable when heated 

 at moderate temperatures in an inert atmosphere and in the absence of 



80 A. O. Tischer, J. Biol. Chem. 125, 475 (1938). 

 8' K. C. D. Hickman, Chem. Revs. 34, 51 (1944). 



82 N. A. Milas, U. S. Pat. 2,173,629 (Sept. 19, 1939). 



83 H. N. Holmes and R. E. Corbet, J. Am. Chem. Soc. 59, 2042 (1937). 

 8" J. G. Baxter and C. D. Robeson, J. Am. Chem. Soc. 64, 2411 (1942). 



