II. CHEMISTRY AND INDUSTRIAL PREPARATION 



31 



to gi\e a deep blue color^^ which absorbs in tlie visible region of the spectrum 

 with a characteristic and well-defined maximum at 620 m/x. The color is not 

 staiile, and after a few minutes it fades out with the appearance of a new 

 maximum at 580 m/x. The maximum at 620 m/i has been used for a long 

 time to measure the actixntv of vitamin A in liver oils and other vitamin A 



5000 



4000 



3000 



2000 _ 



1000 _ 



500 10 20 30 40 50 60 70 80 90600 10 20 30 40 50 60 70 80 90 700 



Wavelength, m/j 



Fig. 5. The absorption spectrum of the reaction product of the all-</-a/is vitamin 

 Ai with antimonj' trichloride in chloroform (cf. refs. 87 and 92). 



preparations. An absorption curve of this color obtained with pure vitamm 

 Ai is shown in Fig. 5. The maximum E\'^^^_ (620 mju) for the a\\-trans 

 vitamin Ai is 5070, and that for the aW-trans vitamin Ai acetate is 4420.^ 

 Vitamin Ai reacts rapidly with maleic anhydride to form an adduct" 

 which fails to give a blue color with antimony trichloride in chloroform. 

 Mineral acids are known to destroy vitamin Ai and its isomers, and, if this 

 reaction is carried out with hydrogen chloride in ethanol, anhydrovitamin 



9« F. H. Carr and E. A. Price, Biochem. J. 20, 498 (1926). 



" K. Kawakami, Sci. Papers Inst. Phys. Chem. Research (Tokyo) 26, 77 (1935). 



