CONSTITUTION OF ANTHOCYANINS 



75 



layer with a blue colour. With sodium carbonate it gives a violet or 

 blue colour (green when the colourless isomer is also present) ; with 

 lead acetate, it gives a blue precipitate. 



The violet modification of anthocyanin was obtained apparently 

 by precipitating a solution of cyanin chloride with lead acetate, and 

 decomposing the lead salt with excess of sulphuretted hydrogen. On 

 filtration and evaporation, the violet form of the pigment is obtained. 



The colourless modification of the pigment is soluble in ether; 

 on evaporation of the ether it remains in the form of colourless crystals, 

 which give an intense red colour on heating with hydrochloric acid. 

 With alkalies it gives a yellow colour, but is apparently not a flavone 

 (see p. 78). 



As regards the constitution of anthocyanin, Willstatter, in this 

 first paper, is of the opinion that the pigment of Centaurea contains a 

 nucleus of the following type, colour being due to the presence of the 

 quinonoid and tetravalent oxygen : 



= 



the above would represent the violet pigment as an inner oxonium salt. 

 Under certain conditions, as we have seen, a change readily takes place 

 by tautomerism to a colourless isomer: 



HO- 



HO- 



which is really a flavone with an extra hydroxyl in position 2. 



The blue pigment in the plant is the potassium salt of the 

 violet pigment, the position of the potassium being uncertain. 

 If the cell-sap is alkaline, the blue salt predominates, or is alone 

 present. 



