Quinone-imine Dyes 107 



METHYLENE AZURE C. I. NO. 913 



This was first recognized as one of the components of poly- 

 chrome methylene blue by Bemthsen (1885). It is now known 

 to be a mixture, not a simple dye. Definite knowledge of its 

 chemistry has been obtained by Kehrmann (1906), Bemthsen 

 (1906) and MacNeal (1906, 1925). It is regarded as primarily a 

 mixture of azure A and azure B, described below, compounds 

 which Bemthsen and MacNeal have shown simple methods for 

 preparing in relatively pure condition by the oxidation of methy- 

 lene blue. Another oxidation product of methylene blue, de- 

 scribed later by Holmes and French (1926), has been named azure 

 C. Now that these three dyes, azures A, B and C are recognized, 

 it would be most satisfactory if the name methylene azure could 

 be dropped, and users specify the actual dye employed. 



Azure I (Giemsa) is a trade name applied to a secret preparation 

 which appears to be a somewhat variable mixture in which azure B 

 predominates. Azure II (Giemsa) is an intentional mixture of 

 azure I with an equal quantity of methylene blue. Products of 

 these same names are now sold by various companies and they are 

 certainly not all identical with the original Giemsa preparations. 

 They all probably agree, however, in containing azure A and azure 

 B as their chief constituents. 



C13H12X3SCI; MoL Wt. 277.767 

 {A basic dye; absorption maximum 607-610) 



Curve 4 in Fig. 12, p. 108, is a spectrophotometric graph of a 

 typical sample of azure C. 



It is not a textile dye; and up to the present has been manu- 

 factured only on a laboratory scale. A small lot, thus prepared, 

 has been put on sale by one of the American stain companies. 

 This dye, Hke the other azures described below, has up to the pres- 

 ent been prepared only by the oxidation of methylene blue. If 

 they prove sufficiently valuable, a process of manufacture by 

 direct synthesis will undoubtedly be developed. A product thus 

 manufactured would probably be cheaper as well as purer than the 

 present supply. 



