2. THE RHOD AMINES 



The rhodamines are similar to the pyronins except that there is 

 a third benzene ring attached to the central carbon atom and 

 attached to this ring is a carboxyl group in the ortho position. 

 This latter group, altho of acid tendency, does not counteract the 

 basic action of the amino groups, so the dyes are basic in character. 

 Only one of them is of any significance to the biologist, namely: 



CH.CH 



3 ^^^2 



RHODAMINE B C. I. NO. 749 



Synonyms: Rhodamine 0. Brilliant pink. 



CH2CH3 



O /\_N— CH.CH 



"I 

 CI 



GH3'CH2 



I 



COOH 



{A basic dye; absorption maxima about 556.5^ [519]) 



A rhodamine, probably the above dye, has been used by Gries- 

 bach with osmic acid to fix and stain blood simultaneously; by 

 Ehrlich as a component of "neutral" stain mixtures; by Rosen 

 for histological work in contrast to methylene blue; and by others 

 in contrast to methyl green. 



A somewhat different dye, knoTvn as Rhodamine S (C. I. No. 

 743) has been mentioned in the same connection and may have 

 been used for some of the above mentioned purposes. It is not a 

 true rhodamine, however, but belongs to a closely related group of 

 compounds, the succineins; for it does not have the three benzene 

 rings, the radical CgH^COOH being replaced by C2H4COOH. 



In practice the rhodamines are prepared not from xanthene but 

 by the condensation of two molecules of meta-amino phenol, 



NH. 



OH 



with one of phthalic anhydride : 



