Quinone Imine Dyes

a group of dyes that are derivatives of para-quinone imine (I) or para-quinone diimine (II), in which the hydrogen atom of an imine group is replaced by an aromatic residue containing an NH₂ or OH^– group. Among the quinone imine dyes are indophenols (III), indamines (IV), and indoanilines (V) and (VI). Instead of benzene residues, dyes (III), (IV),

(V), and (VI) may contain naphthalene or some other aryl group, and the hydrogen atoms may be replaced by radicals, such as CH₃.

Quinone imine dyes are produced by the concurrent oxidation of para-aminophenols and phenols or para-diamines and amines, as well as by the condensation of para-nitrosophenols with phenols or para-nitrosamines with amines or phenols. Dyes (III), (IV), (V), and (VI) have an intense blue or green color but are not sufficiently stable; they are used as intermediate products in the production of sulfur dyes. Quinone imine dyes with a more complex structure, one containing in the ortho position to the central nitrogen atoms nitrogen, oxygen, or sulfur atoms, which form a heterocycle, are used in the production of azine, oxazine, and thiazine dyes, respectively.

Quinone imine dyes are also commonly used in color photography and in the production of pencils, as well as for dyeing paper and fur. In addition, they are used as chemical indicators.