178 



Biological Stains 



This latter form might also be assumed for the oxazins and thiazins 

 as well, and this type of formula is frequently used for the azins; 

 but the xanthene dyes are more often represented in this form. If 

 this formula is adopted the quinoid ring cannot be accepted as 

 their chromophore. For this reason one of the quinoid formulae 

 seems preferable; and for the sake of uniformity the paraquinoid 

 form will be given in the following pages. It must be remembered, 

 however, that the other formulae are equally admissible; and it is 

 possible that the compounds occur in two or even all three of the 

 different forms. 



q5 



PYRONIN Y 



Synonym: Pyronin G. 

 CH3 CH3 



N_/\_0_/\^N— CH3 



C. I. NO. 739 



CH3 



CI 



\/ c \/ 



H 

 C17H19N2OCI; Mol. Wt. 302.795 



{A basic dye; absorption maximum about 552) 

 Solubility at 26''C: in water 8.96%; in alcohol 0.60% 



This dye, finding occasional application as a biological stain in 

 pre-war days, was not manufactured in America until 1931. For 

 most purposes pyronin B may be substituted for it; but Scudder 

 (1931) finds it necessary in her combined Gram-Pappenheim stain. 



A typical spectral curve of this dye is given in Fig. 23, in which 

 it is compared with pyronin B. This graph, together with the 

 others in this chapter, is from Stotz et al. (1950) in which the spec- 

 trophotometric characteristics of the xanthene dyes are discussed. 



qs 



ACRIDINE RED 3B 



C. I. NO. 740 



This dye, in spite of its name, is not an acridine derivative, but 

 a pyronin, a lower homolog of pyronin G or Y: 



-NH— CH3 

 CI 



CH3— HN_/\_0_/^ 



"c" 



I 

 H 



C15H15N2OCI; Mol. Wt. 274.743 



{A basic dye; absorption maxima: [508] 5Jli7.5) 



