II. CHEMISTRY AND INDUSTRIAL PREPARATION 



49 



Originally'"' this hydiocarhon was tiiought to have a dicyclic structure, 

 but later researches'"""^" demonstrated its monocyclic nature and the pres- 

 ence of six double bonds in conjugation. The most reasonable structure 

 of this hydrocarbon is that represented by formula XCIV. A plausible 

 mechanism of the reaction is that which assumes the formation of two 

 carbonium ion intermediates, XCII and XCIII.'^''" ^^* 



"H3C 



CH3 



Vitamin A 



CH3 



\ 



CH, 



Cn=CII— C=Cn— CH=CH— C=CH— CHs 



\/ 



-CH3 



XCII 



HjC CH3 



CH3 



CH3 



CH— CH=C— CH=CH— CH=C— CH=CH.> 



-CH, 



+H,0 



XCIII 



H3C 



CH, 



CH, 



CH3 



=CH— CH=C— CH=CH— CH=C— CH=CH2 + H+ 



-CHa 



XCIV Anhydrovitamin A 



Anhydrovitamin A is best prepared by the method of Shantz et al.,^'^ 

 who crystallized it from petroleum ether at —70° to give orange prisms, 

 m.p. 76 to 77°. A slightly different method is described by Karrer and 

 Schwyzer.'"' The ultraviolet spectrum (Fig. 10) shows three peaks'^^''' '"« 

 at 351, 371, and 392 m^ with i^l^v values of 2540, 3680, and 3200, respec- 

 tively. The antimony trichloride reaction shows a single band with a 

 maximum at 620, with an is'l'fm. value of 5500, a slightly higher value than 



"* J. R. Edisburj', A. E. Gillam, I. Heilbron, andR. A. Morton, Biochcm. J. 26, 1164 



(1932). 

 "5 P. Meunier, R. Dulou, and A. Vinet, Bull. sac. chim. hiol. 25, 371 (1942); Compt. 



rend. 216, 907 (1943). 

 "6 E. M. Shantz, J. D. Cawley, and N. D. Emhree, ./. .4m. Chem. Soc. 65, 901 (1943). 

 >" P. Karrer and R. Schwyzer, Helv. Chim. Acta 31, 1055 (1948). 

 "8 P. Meunier, Compt. rend. 227, 206 (1948). 



