The Formation of the Anthocyan Pigments of Plants. 121 



to carbon dioxide, ammonia, and acetaldehyde. Hnrtley and Wooton,* win. 

 have made a full study of the reaction, find that dimethylalloxan behaves in 

 a similar manner. W. Traubef has found that benzoquinone and isatin 

 have similar oxidising properties. 



Glycine ethyl ester, NH 2 .CH2.CO.OC 2 H 5 ,t behaves quite differently. With 

 quinone in alcoholic solution it forms the di-ethyl ester of diglycinoquinone, 

 together with hydroquinone ; the amino-acid is not decomposed, since the 

 ester group shields the carboxyl group from attack. 



It is improbable, therefore, in view of these observations that the con- 

 densation between quinone and glycine takes place in the manner suggested 

 by Cooper. 



Ammonia by itself gives a brown coloration with quinone, but if form- 

 aldehyde be added the brown colour is converted into red. No coloration is 

 given on mixing formaldehyde with quinone, bub on the cautious addition 

 of ammonia a red coloration is produced. The colour is very similar to that 

 given by quinone and glycine ; this last mixture gives the same reddish- 

 brown shades when a slight excess of ammonia is added. Similarly, quinone 

 gives no colour with benzaldehyde alone, but a red colour is produced on the 

 addition of ammonia, the colour resembling the red obtained from phenyl- 

 alanine and quinone. Salicylic aldehyde, quinone, and ammonia give rise at 

 first to a red coloration and then to an insoluble brown substance. 



Quinone forms a red coloration alike with glycine, alanine, leucine, 

 tyrosine, phenylalanine, or asparagine. The colours are very similar to, 

 not identical with, one another, and they are formed at much the same rate. 

 The red is reduced immediately by zinc dust and acetic acid, and a colourless 

 solution is obtained (see Section 1). The colour returns slowly on standing, 

 more quickly on warming, and immediately on the addition of a drop of 

 hydrogen peroxide. 



Quinol is converted by an oxydase in presence of glycine into a red 

 pigment ; of its ethers dimethylquinol gives no coloration, and methylquinol 

 a faint pink only, which is, perhaps, due to impurity or to its oxidation to 

 quinone. Methyl arbutin should not, therefore, be capable of giving rise 

 to this red pigment. 



When the oxidation of arbutin at 37° is prolonged, action continues past 

 the red stage. The solution becomes a chestnut brown, a brownish black 

 precipitate is deposited, a little tarry matter appears on the surface, and a 

 marked aromatic odour suggesting the smell of prunes is imparted to the liquid. 



* ' Chem. Soc. Trans.,' 1911, vol. 99, p. 288. 

 t 'Ber.,' 1911, vol. 44, p. 3145. 



% E. Fischer and Schrader, ' Ber.,' 1910, vol. 43, p. 525. 

 VOL. LXXXVII. — B. K 



