CHAPTER VII 

 THE PHENYL METHANE DYES 



ONE of the most important groups of dyes, both from the 

 standpoint of the dyer and from that of the biologist, is a 

 group of substituted methanes, or in other words compounds 

 with a central carbon atom. In methane, CH4, it is possible to re- 

 place any of the hydrogen atoms with methyl, ethyl, or phenyl 

 groups. If one H is replaced with CH3, it becomes ethane, 

 CH3CH3. If two are replaced with CH3 groups it becomes pro- 

 pane, CH3CH2CH3; while if there are three substituent CH3 

 groups it becomes iso-butane: 



CH3 CH3 



\ / 

 C 



/ \ 

 CH3 H 



Similarly if one H is replaced with a phenyl group it becomes 

 phenyl methane or toluene: 



CH3 



if with two it becomes di-phenyl methane: 



if with three it becomes tri-phenyl methane: 



H 



C 



Certain substitution products of the di- and tri-phenyl methanes 

 are among the most powerful dyes known. 



Di- and tri-phenyl methane, themselves, are not dyes, nor are 

 they chromogens. They lack both the chromophore and the auxo- 

 chrome groups. The first step (theoretically) in converting them 

 into dyes is to introduce an -OH group in the place of one of the 

 unsubstituted H atoms of the methane nucleus. The compound 

 thus formed, which bears the same relation to the phenyl methane 

 as alcohol does to methane, is called a carbinol. A carbinol is 

 methyl alcohol in which one or more of the hydrogen atoms may 

 have been replaced with an alkyl radical or a benzene ring. Thus: 



137 



