2IO CAROTENOTDS CONTAINING HYDROXYL GROUPS XI 



Solubility: The solubilities of flavoxanthin are similar to those of xantho- 

 phyll. Flavoxanthin is easily soluble in chloroform, benzene, and acetone, more 

 sparingly in methanol and ethanol, and almost insoluble in petroleum ethei . 



Spectral properties (cf. Fig. 12, p. 352) : 



Solvent Absorption maxima 



Carbon disulphide 479 449 m// 



Chloroform 459 430 m/i 



Petroleum ether 450 421 m/z 



Ethanol 448 421 m/i 



Optical activity: [a]c° = +190° (in benzene). 



Partition test: Flavoxanthin is entirely hypophasic on partition between 

 90% methanol and petroleum ether. 



Chromatographic behaviour: For the separation of flavoxanthin from other 

 phytoxanthins, especially xanthophyll and chrysanthemaxanthin, zinc carbo- 

 nate is a particularly suitable adsorbent^*". A good separation of the pigments 

 can also be achieved by adsorption on calcium carbonate. Benzene is employed 

 as solvent, and ether containing a little methanol is used as eluent. Flavo- 

 xanthin is found below violaxanthin, but above chrysanthemaxanthin, on the 

 chromatogram column. Xanthophyll is found in the lowest part of the column. 



Colour reactions: 



Concentrated sulphuric acid .... deep blue 



Trichloracetic acid blue 



Antimony trichloride in chloroform . blue 



Anhydrous formic acid green 



Picric acid in ether green 



Concentrated aqueous hydrochloric 



acid blue (not very stable, 



cf. violaxanthin) 



Identification and estimation: Flavoxanthin is separated from other phyto- 

 xanthins by adsorption on zinc carbonate. Prolonged washing is required for 

 the separation from chrysanthemaxanthin which may also be present. The 

 pigment is identified by the determination of the absorption maxima and by 

 the colour reaction with hydrochloric acid. 



Physiological behaviour: As would be expected from its structure, flavo- 

 xanthin has no vitamin A activity. 



Derivative 



Flavoxanthin diacetate Z^^YI^qO^^'^'^: The diacetate crystallises from methanol 

 in brilliant orange red leaflets, m.p. 157° (uncorr., evacuated capillary). 

 References p. 214— 2iy. 



