# 1911 Encyclopædia Britannica/Indulines

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​INDULINES, a series of dyestuffs of blue, bluish-red or black shades, formed by the interaction of para-amino azo compounds with primary monamines in the presence of a small quantity of a mineral acid. They were first discovered in 1863 (English patent 3307) by J. Dale and H. Caro, and since then have been examined by many chemists (see O. N. Witt, Ber., 1884, 17, p. 74; O. Fischer and E. Hepp, Ann., 1890, 256, pp. 233 et seq.; F. Kehrmann, Ber., 1891, 24, pp. 584, 2167 et seq.). 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 (Jour. Chem. Soc., 1883, 43, p. 115), which was proved by Fischer and Hepp to be dianilidoquinone dianil, a similar intermediate compound being found shortly afterwards in the naphthalene series. Azophenin, C$_{30}$H$_{24}$N$_4$, 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:
| NH$_2$⋅C$_6$H$_4$N$_2$⋅C$_6$H$_5$+C$_6$H$_5$NH$_2$→HN:C$_6$H$_3$ | N—— | C$_6$H$_4$, |
| NH$_2$⋅C$_6$H$_4$N$_2$⋅C$_6$H$_5$+C$_6$H$_5$NH$_2$→HN:C$_6$H$_3$ | N·C$_6$H$_5$ | C$_6$H$_4$, |
| (aposafranine) |||
or by condensing oxy- and amido-quinones with phenylated ortho-diamines (F. Kehrmann, Ber., 1895, 28, p. 1714):
| HO | C$_6$H$_2$ | O | + | H$_2$N | C$_6$H$_4$= 2H$_2$O | + | O | C$_6$H$_2$ | N·C$_6$H$_5$ | C$_6$H$_4$. |
| O | C$_6$H$_2$ | OH | + | C$_6$H$_5$NH | C$_6$H$_4$= 2H$_2$O | + | HO | C$_6$H$_2$ | N—— | C$_6$H$_4$. |
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.
| NH:C$_6$H$_3$ | N—— | C$_6$H$_4$NH:C$_6$H$_3$ | N—— | C$_{10}$H$_6$ |
| NH:C$_6$H$_3$ | N·C$_6$H$_5$ | C$_6$H$_4$NH:C$_6$H$_3$ | N·C$_6$H$_5$ | C$_{10}$H$_6$ |
| I. Benzindulines. | I. Benzindulines. | II. Isorosindulines. | II. Isorosindulines. | II. Isorosindulines. |
| NH:C$_{10}$H$_5$ | N—— | C$_6$H$_4$NH:C$_{10}$H$_5$ | N—— | C$_{10}$H$_6$ |
| NH:C$_{10}$H$_5$ | N·C$_6$H$_5$ | C$_6$H$_4$NH:C$_{10}$H$_5$ | N·C$_6$H$_5$ | C$_{10}$H$_6$ |
| III. Rosindulines. | III. Rosindulines. | IV. Naphthindulines. | IV. Naphthindulines. | IV. Naphthindulines. |
The rosindulines and naphthindulines have a strongly basic character, and their salts possess a marked red colour and fluorescence. Benzinduline (aposafranine), C$_{18}$H$_{13}$N$_3$, 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-β-naphthylamine; rosinduline from benzene-azo-α-naphthylamine and aniline and naphthinduline from benzene-azo-α-naphthylamine and naphthylamine.