COLOUR AND CONSTITUTION 



66 1 



very high molecular weight and above all non-crystalline, and 

 this makes them unsatisfactory substances to employ in the 

 present discussion. Green 1 has also pointed out that assuming 

 quadrivalent oxygen it is possible to formulate these substances 

 as or///o-quinones as follows : 



HO 



OH 



One or two other cases might be mentioned where the quinone 

 theory offers no real explanation of the presence of colour so 

 far as the substances have been investigated. Particularly 

 interesting is the case of diaminoterephthalicester, where the 

 " quinone " and the Witt theories come in opposition. This red 

 substance which gives colourless salts might, on the quinone 

 theory, be formulated as — 



NH 



CO.,C,H</ 



'2^a iX 8 



< H 

 H 



NH 



when it would be assumed that salt formation produces a true 

 benzene — i.e. a colourless derivative. Kauffmann 2 argues that 

 this is improbable, as the free amine should certainly also be 

 colourless. He explains the colour as being the strong intensi- 

 fying action of the NH 2 groups on the weakly chromophoric 

 C0 2 C 2 H 5 -. 



Although, as stated above, the quinone theory of colour 

 was originated by Armstrong, yet it has been left to others, 



1 Proc. Chem. Soc. 319, 12 (1907). 



2 Loc. cit. p. 33. 



