710 VII. VITAMINS A 



tion of the epoxides of /3- and a-carotenes.^^^-^^^ According to Swern,^*^ 

 peracids attack a tertiary-tertiary double bond, like the A^'^ bond in the (3- 

 ionone ring, in preference to that of any other double bond. This would ex- 

 plain the ready production of epoxides when vitamin A or the carotenes are 

 treated with peracids. 



The characteristic absorption band of vitamin A epoxide is at 272 m/x 

 (chloroform), while with antimony trichloride the absorption maxima is at 

 580 mju. Milas*^ believes that vitamin A epoxide is simultaneously pro- 

 duced, in the synthesis of vitamin A methyl ester, through the dehydro- 

 halogenation method, or from the carbinol. This author also casts some 

 doubt upon the accuracy of the location of the band in the far ultraviolet at 

 272 m/i, as suggested by Karrer and Jucker."* Since there are 4 conjugate 

 double bonds in the molecule, there should be absorption in the region of 

 285-290 van. Support for such an hypothesis is afforded by the dem- 

 onstration of a single band at 285 m^t in an autoxidized sample of pure 

 natural vitamin A"^ kept in methanol under nitrogen for 8 years,^^ which 

 presumalily contained this epoxide. The epoxide of the synthetic methyl 

 ether of vitamin A has a similar band. Moreover, in view of the similarity 

 in the spectrum, there would seem to be some indication that the vitamin A 

 epoxide is identical with the 580 m/x chromogen of van Eekelen et al.,^^^ as 

 well as with the sub vitamin A of Embree and Shantz^^^ and of Hawkins and 

 Hunter. ^*^ 



(J) Kitol 



Embree and Shantz^^® were the j&rst to separate a vitamin-A-like product 

 from whale oil which they called kitol (from a modification of the Greek 

 word for whale, Krjroo-). Although whale oil is the chief soiu'ce of kitol, the 

 latter does occur in fish liver oils; dog-fish liver oil was found to contain 

 0.06%, shark liver oil 0.8%.^*^ Its presence in the liver oil of a fresh-water 

 species of fish, the northern pike, was also established. '^"^ In addition, kitol 

 has been reported in the liver oils of such terrestrial mammals as oxen and 

 sheep. ^^^'^^^ 



Kitol is a dihydric alcohol which has a molecular w^eight about twice 

 that of vitamin A. It occurs in whale liver oil as the ester. The empirical 



ISO p. Karrer and E. Juciker, Helv. Chim. Ada, 2S, 427-430 (194r)). 

 i«i P. Karrer and E. Jucker, Helv. Chim. Ada, US, 471-473 (1945). 



182 D. Swern, J. Am. Chevi. Soc, 69, 1692-1698 (1947). 



183 M. van Eekelen, A. Emmerie, H. W. Julius, and L. K. Wolff, Nature, 132, 171 

 (1933). 



18* N. D. Embree and E. M. Shantz, /. Am. Chem. Soc, 65, 906-909 (1943). 

 186 E. G. E. Hawkins and R. F. Hunter, Biochem. J., 88, 34-37 (1944). 



186 N. D. Embree and E. M. Shantz, /. Am. Chem. Soc, 65, 910-913 (1943). 



187 F. B. Clough, H. M. Kascher, C. D. Robeson, and J. G. Baxter, Science, 105, 436 

 (1947). 



i8« K. Hickman, Ann. Rev. Biochem., 12, 353-396 (1943). 



