v] CONSTITUTION OF ANTHOCYANINS 67 



product. The pigment itself decomposes and melts at 270 C. It 

 gives a deep red colour with acids, even with a trace; with alkalies 

 and ammonia, a greenish-red fluorescent solution : with ferric chloride, 

 a blue-violet coloration. The red colour of the pigment is changed to 

 yellow on standing, or by boiling with hydrogen peroxide. 

 An analysis of the substance, dried in air, gave: 



C H O 



From anthocyanin 46-34% 5-87% 47-79% 



Calculated for C 18 H 26 13 



+ 2CH 3 COOH 46-31 % 5-96 % 47-73 % 



After drying in vacuo over caustic potash: 



C H 



From anthocyanin 48-69% 5-10% 46-21% 



Calculated for C 18 H 26 13 ... 48-00% 5-78% 46-22% 



The molecular weight, found by the lowering of the freezing point 

 of phenol, was 437, and calculated for C 18 H 26 13 it would be 450. 



The number of hydroxyl groups was determined by means of the 

 acetyl derivative which was prepared by boiling the pigment with acetic 

 anhydride. The acetyl derivative crystallises in brown crystalline 

 plates from ethyl acetate. To ascertain the number of hydroxyl 

 groups, the derivative was hydrolysed with barium hydroxide, the acetic 

 acid distilled off, and estimated by means of barium hydroxide. For 

 the molecular weight assumed, the result corresponded with the presence 

 of two hydroxyl groups. The number of carboxyl groups was found 

 by making the potassium salt of anthocyanin by exact neutralisation, 

 and estimating the potassium. For the molecular weight assumed, 

 the result corresponded to three carboxyl groups. 



A sodium bisulphite compound was obtained by shaking an alcoholic 

 solution of the pigment with a concentrated solution of sodium bisulphite. 

 The product formed a pale yellow, extremely unstable, crystalline 

 mass, which was soluble in water, and insoluble in ether, chloroform, 

 carbon bisulphide and aniyl alcohol. The product is regarded by Grafe 

 as an additive compound with an aldehyde group in the pigment, and 

 the anthocyanin colour returns on addition of a trace of a stronger 

 acid. The aldehyde groups were determined by allowing a known 

 amount of sodium bisulphite solution to react with the pigment, and 

 then estimating the excess of bisulphite used. The result was also 

 confirmed by oxidising the anthocyanin bisulphite, and estimating the 



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