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 1863by J. Dale and H. Caro, and since then have been examined by many chemists.
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 naphthaleneseries. 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 oxidationof 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.
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