The Chemistry of Dyestuff. Dyestuffs. XXI. Indamines and Indophenols.

A Manual for Students of Chemistry and Dyeing
By
M. Fort, M.Sc. (Leeds) Late Lecturer in Dyeing in the Bradford Technical College and L. L. Lloyd, Ph.D. (Bern) Lecturer in Organic and Technical Chemistry in the Bradford Technical College
Cambridge: at the University Press 1919
(First edition 1917, reprinted 1919)These derivatives of quinone imide comprise numerous blue and green dyestuffs which, while lacking the stability necessary for use as commercial dyestufls, are valuable intermediate stages in the manufacture of other quinone imide dyestuffs, i.e., of the azine and related classes.

Quinone chlorimides have been obtained by oxidation of p-amidophenol with hypochlorites, while more recently Willstaetter has isolated the monoand diimides of quinone.
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The indophenols and indamines are derivatives of the above p-quinonoid bodies, the azine dyestuffs are derived from the corresponding o-quinonoid compounds.

Oxidation of aniline and p-phenylene diamine, e.g., with chromic acid, gives an indamine, Phenylene Blue:
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Similarly oxidation of dimethyl-p-phenylene diamine and dimethyl aniline gives Bindschedler's Green:
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A second general method of synthesis is by acting on amines having a free p-position with nitrosamines: [-]

If instead of a nitrosamine a nitrosophenol be taken, a similar reaction occurs with production of an indophenol. The indophenols are also obtained by oxidation of a p-diamine in presence of a phenol or naphthol having a free p-position.

Only one of these bodies has found commercial use, namely, Indophenol Blue: [-]

This dyestuff has found a limited use as an addition to the indigo vat, the colourless leuco compound obtained on reduction being soluble in alkalis. Aniline Black has been claimed as a dye of this class, but there are serious objections to such being the case. Thus while Aniline Black is a remarkably stable compound, the indamines and indophenols are very sensitive to the action of acids and decompose by hydrolysis, giving quinones: [-]

Indamines and indophenols are readily obtained by oxidation of corresponding di-p-substituted diphenylamine derivatives. Thus p-p'-diamido-diphenylamine is the leuco compound of Phenylene Blue, and is obtained from it on reduction.