570 VI. CAROTENOIDS AND RELATED COMPOUNDS 



Table 7 

 Comparison of Properties of Flavoxanthin and Chrysanthemaxanthin" 



Property Flavoxanthin Chrysanthemaxanthin 



Empirical formula C40H56O3 C^HseOs 



Number of double bonds 10 10 



Number of hydroxyl groups 2 2 



Number of ethor-bound ox\'|L;ens 1 1 



Melting point, °C 180° 184-185° 



Position in chromatogram Upper Lower 



Absorption maxima (CS2), m^ 479, 449 479, 449 



Absorption maxima (C2H5OH), mix.... 450, 421 450, 421 



Reaction with cone. aq. fICl Blue (unstable) Colorless 



<• P. Karrer and E. Jucker, Helv. Vhim. Acta, 28, 300-315 (1945), p. 305. 



{9) Taraxanthin 



Taraxanthin, which is an isomer of violaxanthin, was first discovered in 

 dandelion flowers {Taraxacum officinale) by Kuhn and Lederer.^^* In 

 harmony with the polyenes containing two ring structures, taraxanthin ab- 

 sorbs 11 molecules of hydrogen on catalytic hydrogenation. The Zerewiti- 

 nof¥ reaction shows the presence of three to four active hydrogens, which 

 must be attached in hydroxyl groups. Taraxanthin and violaxanthin differ 

 in absorption spectra from lutein and zeaxanthin; this is interpreted to 

 mean that the chromophore system of conjugated double bonds must be 

 different. The close similarity in spectra between taraxanthin and 

 violaxanthin must indicate an identical arrangement of the double bonds; 

 the only variation, which is shown by differences in the reaction with hydro- 

 chloric acid and in optical activity, must be ascribed to the differences in the 

 positions of the hydroxyl groups. The empirical formula for taraxanthin 

 is C40H56O4. 



Taraxanthin occurs free in dandelion flowers; it is also present in the 

 esterified form in the flowers of the coltsfoot (Tussilago farfara) ,^^^ as well as 

 in those of the Fall hawkbit {Leontodon autumnalis) ,^^^ the buttercup 

 {Ranunculus acris),'^^^ and the balsam, touch-me-not, or yellow snapweed 

 {Impatiens noli me tangere).'^^^ In the last case, the pigment consists almost 

 entirely of taraxanthin. According to Zechmeister and Tuzson,-"! a 

 fraction of the pigment of the sunflower {Helianthus annuus) consists of the 

 same oxygen-containing polyene. Taraxanthin occurs in the rose hips of 

 Rosa canina, R. eglanteria, and R. damascena Mill.,^^^-^'^ and likewise in the 

 flowers of Ulex europaeus (furze, gorse).^"" Strain^*^ found that the leaves 

 of 1 1 species of cycads contained taraxanthin which was identical with that 

 obtained from dandelions. The presence of this pigment has also been 



