T 



CHAPTER V 



THE QUINONE-IMIDE DYES 



HE dyes of the quinone-imide group contain two chromophore 

 groups, the indamin group — N = , and the quinoid benzene 

 ring 



They are derivatives of the theoretical compound paraquinone 

 imide, which, if it existed in its free state, would have the formula 



HN_/"~V=NH 



In the typical indamin formula one of the imide hydrogen atoms is 

 replaced by a phenyl group, thus: 



/^ N_/— \_NH 



In the thiazins the introduction of a sulfur atom, attached to 

 both the phenyl and the quinone groups, forms a third closed ring, 



as: 



/\_S _/\=NH 



■N= 



imido-thio-diphenylimide 



In the oxazins, an oxygen atom takes the place of the sulfur of the 

 thiazins, thus: 



\/\_0_/\=NH 



oxazin 



1. THE INDAMINS 



No dye in this group is a common biological stain. The follow- 

 ing are occasionally mentioned, however, in connection with 

 histology : 



Bindschedler's green. A tetramethyl indamin. C. I. No. 819. 



Toluylene blue. A diamido, dimethyl indamin. C. I. No. 820. 



2. THE THIAZINS 



The thiazins constitute one of the most important groups of 

 dyes from the standpoint of the biologist; while for textile dying 

 the group contains but a small number of dyes of any importance. 

 In these compounds, as mentioned above, the two benzene rings 

 are further joined by a sulfur atom. 



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