M. Wheldale 123 



(d) From artificially synthesised flavones (names not given). The 

 resulting pigment had the properties of anthocyanin. 



As regards the conversion of anthocyanin into flavone by oxidation 

 the following method was adopted by Combes (10) : "Le pigment antho- 

 cyanique extrait des feuilles rouges Vigne-vierge (Ampelopsis hederacea), 

 purifie par deux cristallisations dans I'alcool et trois cristallisations dans 

 I'eau, et dissous dans I'alcool a 90°, donne una solution de couleur 

 pourpre, qui, additionnee de son volume d'eau oxygen^e, passe pen a 

 peu au rouge-brun, puis au jaune. De la solution jaune, ainsi obtenue, 

 j'ai extrait un pigment jaune-brun cristallis6 en aiguilles groupees en 

 rosettes." 



The artificial yellow pigment was found to have the same projwrties 

 and melting point as the natural yellow pigment and was considered to 

 be a flavone. 



In the absence of further evidence, it is difficult to avoid making 

 the following criticism of the experiment just quoted. Since no 

 mention is made of any methods employed in the preparation of 

 crystalline anthocyanin from Ampelopsis, it is highly probable that 

 this product contained flavone as impurity, since most careful purifica- 

 tion is necessary to remove all traces of flavone. Thus, from a mixture 

 of flavone and anthocyanin extracted from Antirrhinum, both pigments 

 will crystallise out together in plates which have, in spite of the presence 

 of flavone, a deep red colour. If the mixture from Ampelopsis were of 

 such a nature, on treating with hydrogen peroxide, the anthocyanin 

 would be decomposed though not necessarily into flavone, and the 

 flavone present as imjjurity could then be extracted from the resulting 

 solution. 



A similar observation, however, to the above is made by Will- 

 statter(36), with regard to Cornflower anthocyanin. " Eine interes.sante 

 Umwandlung erleidet das Cyanidin, wenn wir seine alkoholische Losung 

 mit verdlinntem Wasserstiiffsupero.xyd anstatt mit Wasser erwarmen. 

 Nach der Entfarbung setzen wir einige Tropfen verdihinter Salzsaure 

 zu und erhitzen im Wasserbad weiter. Die Fliissigkeit wird gelb, 

 durch Extrahieren mit Ather lasst sich ein Produkt isolieren, das 

 schone, hellgelbe Krystalle bildet und mit Alkalien tief gelbe Losungen 

 liefert." 



From the above one would make the deduction that, if the antho- 

 cyanin from Cornflower were pure from flavone, a flavone might be 

 formed by destruction, though not necessarily oxidation, of the antho- 

 cyanin. 



