i6 ' ESCHSCHOLTZXANTHIN 323 



Colour reactions: In contrast to violaxanthin, taraxanthin in ethereal 

 solution does not give a blue colouration on shaking with concentrated aqueous 

 hydrochloric acid. 



Detection and estimation: Taraxanthin is separated from other phyto- 

 xanthins by adsorption on zinc carbonate from benzene solution. It can be 

 identified by the determination of the absorption maxima and by the negative 

 hydrochloric acid reaction. For the colourimetric determination, cf. Kuhn and 

 Brockmann^^. 



Cis-trans Isomers of Taraxanthin 



Zechmeister and Tuzson^^ studied the behaviour of taraxanthin in the 

 presence of iodine and found that the chromatogram of the reaction products 

 contained several bands which were ascribed to cis-trans isomers of natural 

 taraxanthin. Three neo-taraxanthins could be distinguished; they were charac- 

 terised by their absorption spectra in carbon disulphide. None of these pigments 

 has yet been obtained in the crystalline state. 



Solvent: Absorption maxima: 



Neo-taraxanthin A 494.5 464 434 m^ 



Neo-taraxanthin B 497 470.5 443 m^ 



Neo-taraxanthin C 480 449 m// 



Taraxanthin (natural) . . . 501 469 440 m/z 



16. ESCHSCHOLTZXANTHIN 



In the course of investigations on the pigments from the blossoms of 

 Eschscholtzia calif ornica, Strain^^ discovered a previously unknown carotenoid 

 for which he proposed the term eschscholtzxanthin. 



For the isolation of the pigment, the blossoms are dried at 45-47°, finely ground 

 and extracted with petroleum ether. The extract is concentrated and saponified with 

 methanolic potassium hydroxide. The pigments are separated into epiphasic and 

 hypophasic fractions, and the latter are extracted with ether. The ethereal solution 

 is concentrated in vacuum and on cooUng most of the eschscholtzxanthin crystallises 

 out. About 4 g of crude product are obtained from 1.15 kg of dried blossoms. The 

 pigment is purified by repeated re-crystallisation from acetone or chromatographic 

 absorption. (Products of equal purity are obtained by the two methods). 



Only a beginning has been made in the elucidation of the constitution of 

 eschscholtzxanthin. The molecular formula is C40H54O2 (± Hg)*. The two 

 oxygen atoms are present as hydroxyl groups. On microhydrogenation the 

 pigment takes up 12 mols of hydrogen. The long-wavelength location of the 



The analytical figures are in better agreement with the formula C^QHggOg than with 

 the formula C4QHg402, but the differences are too small to reach a definite conclusion. 



References p. 341—343. 



