VIIl] 



AROMATIC COMPOUNDS 



117 



species. The pigments themselves with one exception have not been 

 obtained in the crystalline state, but crystalline compounds with acids 

 have been prepared both of the glucosidal and non-glucosidal forms. 



All the pigments so far described appear to be derived from three 

 fundamental compounds, pelargonidin, cyanidin and delphinidin, of which 

 the chlorides are represented thus : 



CI 



CI 



HO 



OH 



HO 



OH H 



Pelargonidin chloride 



PH 

 OH 



OH H 



Cyanidin chloride 



CI 



HO 



/N^ 



PH 



OH 

 OH 



C-OH 



V^c/ 



OH H 



Delphinidin chloride 



It has been suggested, at least in the case of cyanidin, the pigment 

 of the Cornflower {Centaurea Cyanus), that the pigment itself is a neutral 

 substance, purple in colour and of the following structure ( Willstatter, 

 28,31): 



/N^ 



PH 

 OH 



C~OH 



\^C^ 

 OH H 



Further, that the blue pigment of the flower is the potassium salt of the 

 purple, and the red acid salt, cyanidin chloride, depicted above, is a so- 

 called oxonium compound of the purple. 



Pelargonidin, moreover, has been prepared synthetically (Willstatter 

 and Zechmeister, 33) 



The above three pigments, either as glucosides or in the form of 

 methylated derivatives, are found in a number of plants which are listed 

 below (Willstatter, etc., 29, 32). The sugar residues or methyl groups 

 may, of course, occupy different positions, thus giving rise to isomers : 



