106 AROMATIC COMPOUNDS AND [ch. 



true anthocyan pigment but has, it is suggested, an open formation 

 (Willstatter, 36): 



/<x, OH H ^ ^OH 



C— OH 



It is said, however, to contain small quantities of a substance iden- 

 tical with natural cyanidin from the Cornflower (Willstatter, 36). The 

 fact that small quantities of a natural anthocyan pigment can be obtained 

 artificially from a hydroxyflavonol by reduction does not necessarily imply 

 that one class is derived from the other in the living plant. 



From the above reaction of quercetin the result follows that when 

 many plant extracts [most plants (see p. 94) contain flavone or flavonol 

 pigments] are treated with nascent hydrogen, artificial anthocyan pig- 

 ment is produced. Moreover, it seems probable that if the yellow 

 pigments acted upon are in the glucosidal state, and if the reduction 

 takes place in the cold, allocyanin (the glucoside of allocyanidin) is 

 formed and the product is not extracted from solution by amyl alcohol. 

 But if the flavone is non-glucosidal, or if the solution is boiled before or 

 after reduction, then allocyanidin (non-glucosidal) is formed and is 

 extracted by amyl alcohol. 



Expt. 109. Formation of allocyanidin from quercetin. Make an alcoholic solution 

 of a little of the glucoside of quercetin prepared from either Narcissus or Clieiranthux 

 (see Expts. 98 and 100). Acidify with a little strong hydrochloric acid and heat on a 

 water-bath. Add a little zinc dust from time to time. A brilliant magenta colour 

 due to allocyanidin is produced. To a little of this solution add some alkali : a green 

 colour is produced. If the alcohol and hydrochloric acid are evaporated off, and a 

 little water and sulphuric acid added, on shaking up with amyl alcohol, all the 

 allocyanidin passes into the amyl alcohol. (The distribution of the allocyanidin in 

 the amyl alcohol is greater with aqueous sulphuric acid than with aqueous hydro- 

 chloric acid.) 



Expt. 110. Formation of allocyanin from quercetin. Make a suspension of the 

 glucoside of quercetin from Cheiranthiis or Narcissus (see Expts. 98 and 100) in about 2X 

 sulphuric acid, and then add zinc dust (or a drop of merciuy about the size of a pea 

 and a little magnesium powder) in the cold. The red or magenta colour is gradually 

 developed. Divide the coloured solution into two parts in two test-tubes. Boil one 

 for .5-10 minutes. Then add amyl alcohol to each. In the unboiled test-tube the 

 amyl alcohcrl extracts no colour, since allocyanin is present. In the boiled test-tube 

 allocyanidin is taken up by the amyl alcohol as in Expt. 109. 



