REACTIONS OF THE QUINONES 



441 



quinone. Most of such products are red. That the reaction involves the ke- 

 tone groups of the quinone was suggested by Cooper (1913) when she ob- 

 served that no reaction occurs with p-benzoquinone dioxime. The role 

 of the amino group of the amino acid was confirmed by showing that prior 

 reaction of the amino acid with formaldehyde abolishes the 1,4 addition. 

 The rate of the 1 ,4 addition of various amines depends on the pK^ of the 

 amino group (Mason, 1955). The relative reactivities of amino acids and 

 related compounds with p-benzoquinone and toluquinone were given by 

 Cooper and Haines (1928) (see accompanying tabulation). Indoles with 



free 3-positions react with various quinones (p-Q, o-Q, 1,4-NQ, and 1,2-NQ) 

 to yield intensely colored indolylquinones (Bu'Lock and Harley-Mason, 

 1951). The reaction sequence was written as: 



CC 



OH 



-H 



-2 H 



oo^ 



