ANTHOXANTHINS 



335 



CH30^7 



o 



/8\/\ 



OH 



HO 



OH 



O— C5H3O, 



OH CO 

 Quercitrin glucoside 



YELLOW COLOURING MATTERS DERIVED FROM XANTHOME. 

 There are as yet only three colouring matters known to 

 belong to this group, one of which, euxanthone, does not occur 

 in plants, but in Indian yellow obtained from camel's urine ; 

 it has the formula (i.) — 



(I.) 



HO 



CO OH 



Gentisin (11.), a yellow colouring matter occurring in Gen- 

 tiana lutea, is a methyoxyl derivative of the above — 



O 



(II.) 



HO 



OCH, 



Datiscetin occurring in the form of a glucoside, Datiscin, in 

 Datisca cannabina, whose constitution is uncertain. 



Properties of Anthoxanthins. 



1. These colouring matters are mostly yellow crystalline 

 solids. 



2. From their solutions they may be precipitated by lead 

 acetate, the precipitate being yellow, orange, or red. 



3. With ferric chloride a dull green or sometimes a red- 

 brown coloration results, 



4. On fusion with alkali, decomposition ensues, phloro- 

 glucinol and protocatechuic acid being commonly formed, and 

 sometimes resorcinol, resorcylic, or hydroxybenzoic acids. 



The solubility of the anthoxanthins in acids is due to the 

 peculiar basic properties of the oxygen atom taking part in 

 the ring formation. The basic nature of the oxygen atom in 



