124 



REACTIONS INVOLVED IN 



[CH. 



in behaviour, together with the solubility in amyl alcohol and the 

 green reaction with alkalies, he considers to be a complete proof of the 

 identity of the two pigments. 



The author, in conjunction with Bassett (255), has prepared red 

 products from both quercetin and apigenin. In the case of apigenin, 

 the substance was analysed and found to be a reduction product, but 

 its reaction with alkalies in no way resembled that of anthocyanin. On 

 the other hand, there is every reason to believe that the anthocyanin 

 of Antirrhinum may be derived from apigenin by oxidation and con- 

 densation. Hence, in the only instance where both artificial and 

 natural anthocyanins have been obtained from a flavone and have 

 been analysed, they appear to be by no means identical. 



More recently Willstatter (257) has investigated the problem of the 

 artificial formation of anthocyanin, and maintains that two substances 

 are produced when quercetin is reduced with nascent hydrogen. In 

 his experiments, an alcoholic solution of quercetin acidified with hydro- 

 chloric acid is reduced with sodium amalgam or magnesium. A purplish- 

 red product is obtained, and the bulk of this substance he terms allo- 

 cyanidin ; on the basis of analysis (by combustion) of the product he 

 suggests the following constitution and reactions: 



O OH OH/H 



HO/Y\ <^ ^QH HOf" 



V/X/OH 



H <r +2 H 8 ^ 



O 



Quercetin 



Allocyanidin forms a crystalline compound with hydrochloric acid, 

 but is unstable on heating with the dilute acid. When, however, the 

 crude solution obtained from the reduction of quercetin is diluted and 

 heated, it does not entirely lose colour owing to the presence, in Will- 

 statter's opinion, of a small amount of a second product. Isolated and 

 analysed, this latter product was found to be identical with cyanidin 

 chloride, and it is suggested that the reaction takes place as follows : 



OCl 



Allocyanidin 



Quercetin 



Cyanidin chloride 



