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Indulines are a series of dyestuffs of blue, bluish-red or black shades, formed by the interaction of para-amino azo compounds with primary monoamines in the presence of a small quantity of a mineral acid. They were first discovered in 1863 by J. Dale and H. Caro, and since then have been examined by many chemists.
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They are derivatives of the eurhodines (aminophenazines, aminonaphthophenazines), and by means of their diazo derivatives can be de-amidated, yielding in this way azonium salts; consequently they may be considered as amidated azonium salts. The first reaction giving a clue to their constitution was the isolation of the intermediate azophenin by O. Witt, which was proved by Fischer and Hepp to be dianilidoquinone dianil, a similar intermediate compound being found shortly afterwards in the naphthalene series. Azophenin, C30H24N4, is prepared by warming quinone dianil with aniline; by melting together quinone, aniline and aniline hydrochloride; or by the action of aniline on para-nitrosophenol or para-nitrosodiphenylamine. The indulines are prepared as mentioned above from aminoazo compounds, or by condensing oxy- and amido-quinones with phenylated ortho-diamines. The indulines may be subdivided into the following groups: (1) benzindulines, derivatives of phenazine; (2) isorosindulines; and (3) rosindulines, both derived from naphthophenazine; and (4) naphthindulines, derived from naphthazine.
The rosindulines and naphthindulines have a strongly basic character, and their salts possess a marked red color and fluorescence. Benzinduline (aposafranine), C16H13N3, is a strong base, but cannot be diazotized, unless it be dissolved in concentrated mineral acids. When warmed with aniline it yields anilido-aposafranine, which may also be obtained by the direct oxidation of ortho-aminodiphenylamine. Isorosinduline is obtained from quinone dichlorimide and phenyl-13-naphthylamine; rosinduline from benzeneazo-a-naphthylamine and aniline and naphthinduline from benzeneazo-a-naphthylamine and naphthylamine.
This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.
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