OrCTTRRENCE AND STRTTTT^RE OF RELATED COAfrOUNDS 707 



ethyl ethers, while isopropyl and the /e?7-biityl ethers were obtained only in 

 impure form. 



a. Vitamin A Methyl Ether. In 1946, Hanze and co-workers'^' pre- 

 pared the pure methyl ether of vitamin A from the crystalline vitamin A 

 alcohol ; they reported that, like other vitamin A ethers, it is a light yellow 

 solid, melting at 33-34°(\, which has an extinction value, E (1%, 1 cm.) 

 of 1600 at the Xj^ax.) of 326 m/x. The biological potency was given as 

 3,000,000 U.S. P. units per gram. The formula and absorption .spectra are 

 sliown here. 



HiC CHj 



\ / 



C 



CHj CH: 



/\ HHlHHHiH 

 HaC C • C : C • C : C • C : C • C : C • CHj- • CHj 



I II 



HzC C 



\ / \ 



C CHj 



Hj 



\'itamin A methyl ether 



The extinction coefficient of vitamin A methyl ether is 1660, which ap- 

 proximates that of \dtamin A. The spectrophotometric absorption also 

 appears to be quite similar to that of the parent free alcohol. The methyl 

 ether of vitamin A produces a blue color with antimony trichloride, which 

 has two maxima. One maximum is at 580 m/u, while the second one is at 

 618-620 m/i. In one preparation in which the extinction coefficient, 

 E (1%, 1 cm., 325-328 m//), was 1415, the corresponding extinction for the 

 colored product with antimony trichloride, E (1%, 1 cm., 620 mju), was 

 found to be 1660. The properties of some vitamin A ethers and related 

 compounds are summarized in Table 10. 



b. Homovitamin A and S-Dehydrohomovitamin A Ethers. Two im- 

 portant synthetic compounds which possess a considerable degree of 

 vitamin A activitj^ are homovitamin A ethyl ether and 5-dehydrohomo- 

 vitamin A ethyl ether. Each of these compounds has one additional car- 

 bon atom on the aliphatic chain. 



Homovitamin A ethyl ether (C21H31OC2H5) is described chemically as 

 [l-(2',6',6'-trimethylcyclohexen-l'-yl)-3,7-dimethyldeca-l,3,5,7-tetraen- 

 yl]-10-ethyl ether, i'*^ The structural formula, including the key for the re- 

 vised numbering system, is given here. 



"6 A. R. Hanze, T. W. Conger, E. C. Wise, and D. I. Weisblat, /. Am. Chem. Soc, 68, 

 1389 (1946). 



i'« N. A. Mila.s, S. W. Lee, C. Schuerch, Jr., R. O. Edgerton, J. T. Plati, F. X. Grossi, 

 Z. Weiss, and M. A. Campbell, J. Am. Chem. Soc, 70, 1591-1596 (1948). 



