346 



PIGMENTS 



salts in the case of the flavones are not stable and do not 



occur in the plant, but the anthocyanidins yield stable oxonium 



salts of the type — 



Cl 



/ 



OH 



CH 



O 



HOC 



I 



C ( >OH 



C 



V_^ 



CH 



\ 

 COH 



COH 



CH 

 HI. 



which is the formula assigned to cyanidin chloride ; this 

 represents the red form of cyanidin in acid solution ; replace- 

 ment of the — Cl by — OH on treatment with alkali permits 

 the formation of an anhydride IV. — 



OH : 



H 



CH O 



/- \^ \ 



oc C C 



1 I II 



CH C COH 



\ /\ / 

 COH CH 



OH 



V. 



OH 



CH O 



OC c c- 



OH 



OH 



CH C COH 

 COH CH 



IV. 



which represents the neutral form of violet tint, while the 

 blue compound occurring in alkaline solution would be formed 

 by introducing the alkali metal into one or more of the 

 hydroxyl groups. 



In the various anthocyanins so far examined, the hydroxy- 



O 



HO 



OH 



OH 



benzopyrilium group which may be represented by the sym- 

 bol R, is the same in all cases ; the variation between the 

 different compounds is due to differences in the number and 

 position of the hydroxyl groups in the benzene ring ; thus 

 the abbreviated formulae V., VI., and VII. — 



