The Production of Anthocyanins and Anthocyanidins. 329 



HO 



(4) These pigments show the same decolorisation in neutral solution, due 

 to isomerisation, and return of colour by the action of acids asvdo the 

 anthocyanins. 



(5) They form red compounds with acids (everything points to these 

 compounds being oxonium salts), are violet or red-violet in neutral solution, 

 and most of them yield blue or blue-green compounds with alkalis, completely 

 resembling in this respect the anthocyanins. 



(6) They are very unstable towards alkalis, as are the anthocyanins. 

 With this evidence may be coupled that of Combes (he. cit.), who, working 



with Ampehpsis hederacea, obtained a yellow and a red pigment (anthocyan), 

 and by reduction of the yellow obtained the red, and conversely by oxidation 

 the red passed back to the yellow. He prepared both of these compounds in 

 crystalline condition and compared their melting points. He did not state 

 whether they were glucosides or no. 



It seems, therefore, that all available evidence favours the author's 

 conclusions that the red pigments obtained by the reduction of the flavonol 

 derivatives and their glucosides are true anthocyanidins and anthocyanins 

 respectively. Prof. Willstatter, when lecturing on this subject at University 

 College, London, in May last, expressed the opinion that they are compounds 

 in which the pyrone ring has been opened up at the oxygen linkage. 

 Comparison of their properties with those of known compounds of the 

 structure suggested does not lend support to this conjecture ; moreover, it 

 would be very difficult to account for their being strong oxonium bases — as 

 they appear to be — if they were of this type, nor could this interpretation 

 supply satisfactory explanations of the change from violet to red on treatment 

 with acids, nor of the fact that the red are more stable than the violet 

 compounds. 



It is of interest to note that Willstatter's work supplies important 

 experimental evidence in favour of the scheme 



H CI CI 



\/ I 



/XX X ~/ \ OTT HO / \/ \/ \^ TT HO \ / 



C< >OH 



jj, oh 



<K } 0K -H 2 

 Jl OH 



c-/ \os 



\A C / X OH Jetton V\ C / X OH +S^O \/\ / \oH 



OH j| reduction. 0H qh O 



O OH H H 



(Myriectin.) Colourless or faintly coloured Anthoeyan pigment. 



Flavonol derivative. intermediate product. 



already put forward by the author* to explain the formation of the 



* Loc. cit., p. 449. 



