344 PIGMENTS 



PREPARATION OF PROPERTIES OF ANTHOCYANINS. 



The first representative of the class to be isolated in a 

 state of purity by Willstatter and Everest * was cyanin, the 

 blue colouring matter of the cornflower, Centaurea cyanus, and 

 of Rosa gallica ; closely related to this substance are the 

 anthocyanins of the cranberry (idaein), the bilberry (myrtilHn), 

 of blue grapes (cenin), of Delphinium consolida (delphinin), 

 and of Pelargonium zonale, var. meteor (pelargonin), Althaea 

 rosea (althsein), and Malva sylvestris (malvin). 



The methods employed for the extraction and isolation 

 of the anthocyanins vary with the material employed. f In 

 some cases the pigment is extracted with water, as in the case 

 of cyanin from Centaurea cyanus, the blue cornflower, in others 

 with alcohol, e.g. Pelargonium, and in others again, such as 

 the rose and the hollyhock, by means of a hydrochloric acid 

 solution of methylalcohol. These facts may be illustrated by 

 the two following examples : — 



The method recommended in the case of grape skins is % as 

 follows : Extract the skins in the cold with glacial acetic 

 acid and precipitate the dark red filtrate with ether ; by 

 heating the deposit so obtained with a solution of picric acid 

 a crystalline picrate is formed which separates out on cooling. 



For the preparation of cyanin chloride, the following 

 method was employed by Willstatter and Mallison § : 700 

 grams of deep red dahlia petals were extracted with glacial 

 acetic acid ; the extract was mixed with methyl alcoholic 

 hydrogen chloride and precipitated with ether ; the amorphous 

 precipitate dissolved in cold 7 per cent hydrochloric acid on 

 standing yielded 7-4 grams of pure cyanin chloride. 



The isolation of the anthocyanins depends upon the for- 

 mation of sparingly soluble oxonium salts with various acids 

 such as picric, tannic, hydrochloric and acetic. The formation 

 of a crystalline acetate of pelargonidin is easily demonstrated 

 by placing a petal of pelargonium on a shde, covering it with 



* Willstatter and Everest : " Annalen," 1913, 401, 189. 

 t Cf. Willstatter and Mieg : id., 1915, 408, 61 ; also Willstatter and 

 Bolton : id., 1915, 408, 42. 



+ Willstatter and Zollinger : id., 1915, 408, 83 ; 1916, 412, 195. 

 § Willstatter and Mallison : id., 1915. 408, 147. 



