8 XANTHOPHYLL 203 



Melting point: 193° corr. 



Solubility: Xanthophyll is easily soluble in chloroform, benzene, acetone, 

 ether and carbon disulphide, sparingly soluble in ethanol and methanol, and 

 almost insoluble in petroleum ether, i g of xanthophyll dissolves in about 700 g 

 of boiling methanol. 



Spectral properties (cf. Fig. 11, p. 352) 



Solvent: Absorption maxima}'^'' 



Carbon disulphide 508 475 445 m// 



Chloroform 487 456 428 m/f 



« Ethanol 476 446.5 420 vafi 



Petrol 477.5 447.5 420 van 



Methanol .473.5 4-44" 418 m/z 



Solutions of xanthophyll in carbon disulphide are red. Dilute solutions in 

 benzene, ethano', ether and chloroform are golden yellow, while concentrated 

 solutions in these solvents are orange in colour. 



Optical activity: Xanthophyll, like a-carotene exhibits strong optical activity. 

 The specific rotation is [aYcd = +^45° (i^ ethyl acetate), [a]^^ = +160° (in 

 chloroform) . 



Colour reactions*: Xanthophyll dissolves in concentrated sulphuric acid 

 first with a green, then with a blue colouration. Concentrated formic acid gives 

 a bright green, trichloracetic acid a dark blue, and antimony trichloride in 

 chloroform solution an intense dark blue colouration. 



Partition test: On partition between petroleum ether and 90 % methanol, 

 xanthophyll is found in the lower layer. 



Chromatographic behaviour: Xanthophyll is easily adsorbed on calcium 

 carbonate and zinc carbonate from benzene solution. It is eluted with ether 

 containing a few per cent of methanol. 



Detection and estimation: Xanthophyll is separated from other phyto- 

 xanthins by adsorption on zinc carbonate (or calcium carbonate). It can be 

 identified by a determination of the absorption maxima. According to Kuhn 

 and Brockmann^^^, the colourimetric determination can be carried out using 

 a standard solution of azobenzene in ethanol. 



Physiological properties: Xanthophyll possesses no vitamin A activity. 

 According to voN Euler, Karrer and Zubrys, however, a vitamin A-active 

 product is formed on treating the phytoxanthin with phosphorous tribromide^^^. 



Concerning the colour intensity of the antimony trichloride reaction, cf. H. v. Euler, 

 P. Karrer and M. Rydbom, Ber. 62 (1929) 2445. 



References p. 214-21^. 



