608 VI. CAROTENOIDS AND RELATED COMPOUNDS 



phore system has not been altered. This is beautifully illustrated in the 

 results of Kuhn and Brockmann,^'^'^''^ Kuhn and Grundmann,^^° and Kuhn 

 and Deutsch,''" summarized in Table 14. The absorption spectra of 

 rhodoxanthin dioxime are considerably shifted toward the ultraviolet por- 

 tion of the spectrum as compared with those for free rhodoxanthin. The 

 same has been shown to occur when lycopenal is treated with hydroxyla- 

 mine with the resultant formation of lycopenal oxime. In both of these 

 instances, it is certain that the ketone group which combines with the 

 hydroxylamine must have been a part of the system of conjugated double 

 bonds. On the other hand, the dioximes of dihydrorhodoxanthin and of 

 jS-carotenone, as well as the monoximes of semi-iS-carotenone and of aza- 

 frinone, have absorption spectra identical with those of the corresponding 

 free ketones. Since the jS-carotenone is a tetraketone, while it forms only a 

 dioxime, it must be assumed that the two combined ketone groups are not 

 concerned with the conjugated system. A similar relationship exists in the 

 case of the monoxime of the diketone, semi-jS-carotenone. 



Table 14 

 Comparison of .Absorption Spectra of Oximes ok ("arotenoids with Those of the 



Free Ketones" 



Compound Solvent Absorption maxima, mM 



Ketone groups as part of system of conjugated double bonds 



Rhodoxanthin Hexane 524,489,458 



Rhodoxanthin (lioxinic Hexane 513,479,451 



Lycopenal Petr. ether 525 . 5, 490 . 5, 455 . 5 



Lycopenal oxime Petr. ether 503 . 5, 471, 442 



Ketone groups combined as oxime independent of system of conjugated double lionds 



Dihydrorhodoxanthin Hexane 480, 449, 422 



Dihydrorhodoxanthin dioxime Hexane 480, 449, 422 



|3-Carotenone Petr. ether 502, 468, 440 



/3-Carotenone dioxime Petr. ether 502, 468, 440 



Semi-^-carotenone Petr. ether 501 , 470, 446 



Semi-/3-carotenone oxime Petr. ether 501,470,446 ^ 



Azafrinone Petr. ether 454, 429 



Azafrinone oxime Petr. ether 454, 429 



" L. Zechmeister, Die Carotinoide, Springer, Berlin, 1934, p. 67. 



Another factor which may profoundly affect the position of the absorp- 

 tion maxima is the solvent employed. Most dilute solutions of the carote- 

 noids are an intense yellow, while concentrated solutions are deeply orange 

 colored. In carbon disulfide, carotene is reddish brown, in chloroform a 

 brownish yellow, and in ether it appears as a greenish yellow solution. 

 When a cold-saturated solution of carotene in carbon disulfide is poured 

 through filter paper, it produces orange-red spots. Under similar condi- 

 tions, xanthophyll gives a yellow color, while the lycopene specks are from a 

 flesh-red to a chocolate-brown. 2^- ^'^^ 



"» H. H. Escher, Zur Kermtnis des Carotins und des Lycopins, Dissertation, Zurich, 

 1909. Cited by L. Zechmeister, Die Carotinoide, 1934, p. 155. 



