ANTHOCYANINS 347 



OH OH 



R—<^ \oH R— \ /^^ R— \ /OH 



OH 



V. VI. vn. 



represent pelargonidin, cyanidin, and delphinidin respectively. 



It must be borne in mind that the anthocyanins are 

 glucosides, and as a rule occur in the plant in this form ; 

 occasionally, however, they occur free as sugar-free antho- 

 cyanidins ; thus on one occasion Willstatter found in the case 

 of the black AHcante grape as much as 12 per cent of the pig- 

 ment in the sugar-free condition. 



To distinguish between an anthocyanin glucoside and a 

 non-glucosidal anthocyanidin, Willstatter and Everest shake 

 the solution of the pigment in 0-5 per cent hydrochloric acid 

 with amyl alcohol ; the glucoside anthocyanins remain in the 

 aqueous layer, while the sugar-free anthocyanidins pass into 

 the amyl alcohol. 



The relations between some anthocyanin glucosides and 

 their corresponding anthocyanidins is given in the following 

 list :— 



Pelargonin is a diglucoside of pelargonidin. 



Callistephin ,, monoglucoside of pelargonidin. 



Cyanin ,, diglucoside of cyanidin. 



Peonin ,, diglucoside of peonidin (a monomethyl ether * of cyanidin). 



Idaein ,, monogalactoside of cyanidin. 



Delphinin ,, diglucoside of delphinidin united to /j-hydroxy-benzoic 

 acid. 



Violanin ,, rhamnoside of delphinidin. 



Myrtillin ,, monoglucoside of myrtillidin (a monomethyl ether * of 

 delphinidin). 



Malvin ,, diglucoside of malvidin (a monomethyl ether of del- 



phinidin) . 



(Enin ,, monoglucoside of oenidin (a dimethyl ether * of del- 



phinidin). 



The conversion of the flavonol quercetin I. into the antho- 

 cyanidin cyanidin II. was first carried out by Willstatter and 

 Mallison,t and thus the first synthesis of an anthocyanin was 

 effected, since flavonol had already been synthesized by 



* The point of attachment of the methoxyl groups in the compounds 

 is not known with certainty. 



t Willstatter and Mallison : " Sitzungsber, Kgl. Preuss. Akad. d. 

 Wiss.," 1914, 769. 



