448 



Mr. A. E. Everest. 



On a previous occasion attempts to reduce cyanin (the pigment of the 

 cornflower*) to a colourless compound which could be re-oxidised to the 

 pigment had failed. Powdered zinc and acetic acid were used, hot — the 

 pigment was decolorised, but the red colour was not reproduced on addition 

 of hydrogen peroxide. Despite this fact, the author, for comparison, treated 

 a small quantity of cyanin chloride in 2N hydrochloric acid with much finely 

 granulated zinc, so that vigorous evolution of hydrogen ensued. The reaction 

 was carried out in the cold, and, as in the cases mentioned above, decolorisation 

 rapidly set in, but on decanting the decolorised solution and adding hydrogen 

 peroxide the colour reappeared. The glucoside was not hydrolysed by this 

 process. 



In every case, also with cyanin chloride, when treated with hydrogen 

 peroxide in the cold, the red acid solution of the anthocyanin passed to 

 a yellow, then became colourless. It would thus seem that the balance of 

 reducing powers present in an anthocyan-containing flower must be very finely 

 adjusted, for it appears necessary that the reducing body present should be 

 powerful enough to reduce as far as the anthocyanin stage, but not powerful 

 enough to take the pigment further to the colourless condition. 



It has been placed beyond doubt that the change from yellow to red may 

 be accomplished by reduction alone, thus confirming the results of Combes, 

 and, still further, that the change from glucoside flavone or flavonol to 

 anthocyanin (glucoside) takes place quite readily without hydrolysis, and 

 that all hypotheses which require a hydrolysis of the glucoside before 

 formation of red pigments can, in the light of the evidence of Willstatter 

 and Everest, that the anthocyanidins do not exist in plants, and the further 

 evidence now brought forward, that flavone or flavonol glucosides readily 

 yield anthocyanins without intermediate formation of anthocyanidins, be 

 discarded as unnecessary. 



Whether all the yellow glucosides of the flavone and flavonol series are 

 capable of producing corresponding anthocyanins remains to be proved by 

 future work. The author failed to observe such formation in the case of 

 Primula sinensis (Giant white), mimosa, and white hyacinth. (Whites tested 

 with ammonia gave yellow.) 



Whether the red pigments described above should be considered as mere 

 hydroflavone derivatives as I, or as some such anhydro-compound of them, II, 

 remains to be proved, but the author considers that the evidence at present 

 available favours some such form as II, where the change has caused the 

 production of a quinonoid structure, as follows : — 



* Willstatter and Everest, loc. ext. 



