ABSTRACT
The characteristic chromophore of the azine dyes is phenazine: a planar, tricyclic dibenzopyrazine unit. Additional aromatic units are also introduced in dyes such as safranine O (phenyl attached to a ring nitrogen), or azocarmine G (phenyl attached to an amino substituent). The anionic substituents are all strongly acidic sulfonates which are fully ionized over the pH range of concern here, but the basicity of the basic dyes varies somewhat. Some azine dyes discussed here are typically very impure because the methods of synthesis inevitably generate mixtures of isomers and homologs. In both azocarmine B and G the planar cationic aminophenazine chromophore is extended by an additional benzo unit; a further phenyl substituent is attached to a ring nitrogen. Nigrosine WS results from heating nitrobenzene with aniline, to produce a complex mixture of basic azine dyes, which are then sulfonated. An example of an anionic is diaminophenazine thought to be present in nigrosine WS is illustrated.
