THE ANTHOXANTHINS. 



The yellow plant pigments usually called flavones and xanthones are 

 most conveniently termed the anthoxanthins, the term used in 1835 by 

 Marquart and again suggested by Willstatter in 1913 on account of their 

 similarity to the anthocyans. 



The anthoxanthins are derived from the complex benzene-y-pyrone 

 nucleus. The y-pyrone nucleus is the heterocyclic six-membered ring con- 

 taining an oxygen atom and a keto group in the para- or y- 

 position to the oxygen atom. The keto group in this ring 

 does not behave in all respects like a ketone group ; it forms 

 no derivative with hydroxylamine. The oxygen atom is also 

 peculiar in its properties ; it is basic and combines with mineral 

 acids to form salts, the oxygen atom becoming quadrivalent. 



Flavone and xanthone are phenyl derivatives of benzo-y- 

 pyrone. The yellow pigments are hydroxy derivatives of: 



CO 



Flavonol Xanthone. 



or 

 hydroxyflavone. 



The constitution of the anthoxanthins has been shown to be the follow- 

 ing: 



OH 



Chrysin 



or 

 i, 3-dihydroxyflavone. 



OH CO 



Apigenin 



or 



I, 3, 4'-trihydroxy- 

 flavone. 



OH CO 



Luteolin 

 or 



i. 3. 3', 4'. 



tetrahydroxy- 



flavone. 



H CO 



Galangin 



or 

 i, 3-dihydroxyflavonol. 



O 



Caempferol 



or 



i, 3, 4'-trihydroxy- 

 flavonol. 



)H 

 CO 



Fisetin 



or 



3, 3', 4'-trihydroxy- 

 flavonol. 



338 



