Xanthene Dyes 183 



q30 FAST ACID BLUE R C. I. NO. 760 



Almost the same as: Violamine SB. 



N_/"~\_0 CH. CH3 



CseHaeNaOgSNazCU; MoL Wt. 763.552 



{An acid dye; absorption maximum 53^) 



The dye indexes (both Schultz and the Colour Index) list vi- 

 olamine 3B as almost synonymous with this. Violamine 3B, how- 

 ever, is a mixture containing a small amount of some red dye. 

 Some samples of fast acid blue R, made for textile application, are 

 also mixtures, although pure samples have been obtained. It is 

 hoped that pure dye of this type may become regularly available 

 for use as a biological stain. 



This dye has been recommended by Romell for use in phenolic 

 solution for staining bacteria in soil. In the case of soils (mucks, 

 forest soils, etc.) containing much brownish or reddish matter, 

 this blue dye gives greater visibility of the microorganisms than 

 dyes of the eosin series. 



In practice the rhodamines are prepared not from xanthene but 

 by the condensation of two molecules of dialkyl meta-amino 

 phenols, 



R2N 



/ \_0H 



\_/ 



with one of phthalic anhydride: 



CO 



\ 

 O 



. / 

 CO 



This shows their close relation to the next group of dyes, namely 

 the fluoran derivatives, which as will be seen are also prepared 

 from phthalic anhydride. In fact these two groups of dyes, acid 

 and basic respectively, are related in exactly the same way as the 

 rosolic acids and the rosanilins, the one group having hydroxyl 

 radicals where the other has amino groups. 



