568 VI. CAROTENOIDS AND RELATED COMPOUNDS 



earlier, when violaxanthin comes in contact with concentrated hydrochloric 

 acid, or when it is dissolved in chloroform, the properties of the sub- 

 stance are immediately changed and auroxanthin is formed. All the 



HjC CHj HiC CHj 



\ / \ / 



c c 



/ \ H H / \ 



HjC C=C C=.C CH? 



IICH3 CH3 CH3 H^C I I 



IIhhhIhhhhIhhhII I l/H 



^C C c-C:C-c:C'C:C'C:C-C:C-C: C-C:C'C C C 



HO^\c/\\o/"H H^^of^C" ^OH 



Hz CH3 HjC ^2 



Auroxanthin 



properties of auroxanthin correspond with those expected for a compound 

 having two furanoid rings. The correctness of this structure is indicated 

 by the fact that natural and partially synthesized auroxanthin have been 

 shown to be identical. ^^^ 



A comparison of the properties of violaxanthin and auroxanthin is given 

 in Table 6. 



Table 6 

 Comparison of Properties of Violaxanthin and Auroxanthin" 



Property Violaxanthin Auroxanthin 



Empirical formula C40H56O4 C40H56O4 



Number of double bonds 9 9 



Number of conjugated double bonds. . . 9 7 



Hydroxy] groups 2 2 



Ether-bound oxygen 2 2 



Melting point, °C 200° 203° 



Position in chromatogi'am Lower Upper 



Absorption maxima (CS2), m^, 502, 469, 440 454, 423 



Absorption maxima (C2H5OH ),' niM . . . . 471 . 5, 442 . 5, 417 428, 403, 382 



Reaction with 20% aq. HCl Deep-blue (stable) Deep-blue (stable) 



" P. Karrer and E. Jucker, Helv. Chim. Acta, 28, 300-315 (1945). 



{8) Flavoxanthin and Chrysanthemaxanthin 



Flavoxanthin is the lightest yellow carotenoid pigment known. It was 

 discovered by Kuhn and Brockmann,^^^ who prepared it from buttercup 

 petals {Ranunculus acris). It is apparently also present in the Spring 

 goundsel {Senecio vernalis), but it has not been reported to be widely dis- 

 tributed in nature. However, it has been prepared from green leaves by 

 Strain. ^2^' ^^^ Another carotenoid of similar nature which is absent from 

 green leaves has been isolated by Strain'-"* from carrot roots. The so-called 



3*2 P. Karrer, E. Jucker, and J. Rutschmann, Helv. Chim. AcM, 28, 1156-1157 (1945). 

 3" II. A. Sj)o(>hr, J. H. ('. iSmith, II. II. Strain, and H. W. Milner, Carnegie Inst. 

 Wash. Yearbook, No. 35, 198-208 (193G). 



