Basf Aktiengesellschaft

Reinhold Kohlhaupt

Udo Bergmann

Walter Bieg

Lothar Haas

Manfred Gaeng

Matthias Fankhaenel

Guenter Engelhardt

Rolf Fikentscher

Christos Vamvakaris

Helmut Hoch

Gerold Braun

Heinrich Hiller

Heike Kilburg

Matthias Niedenbrueck

Ernst Lang

Manfred Gang

Walter Schweckendiek

Chung-Ji Ischang

A process for purifying indigo comprises extracting an aqueous leuco indigo alkali metal salt solution with an inert solvent under oxygen-excluding conditions and conventionally regenerating the indigo by oxidation.

Purification of indigo

The preparation of anthraquinone imide compounds by condensation of anthraquinone compounds containing at least one primary amino group with halogenized aromatics or by condensation of halogenized anthraquinone compounds with primary aromatic amines, in the presence of a vat-dyeing catalyst and an acid-binding agent in an organic solvent, in which the organic solvent used is an alkyl benzoate.

Preparation of anthraquinone imide compounds

This invention relates to a process for the purification of indigo, wherein the indigo is heated in an inert organic solvent at from 150.degree. to 250.degree. C. and preferably from 180.degree. to 220.degree. C.

Preparation of halogenated indigo

Pure 1-amino-2-phenoxy-4-hydroxyanthraquinone is prepared by reacting 1-amino-2-halo-4-hydroxyanthraquinone with phenol in aqueous suspension at pH 9-13 and 130.degree.-160.degree. C., adjusting the reaction mixture pH to 9.5-11.5 after the reaction has ended, separating the reaction product from the liquid phase, and ,washing it with alkaline hypochlorite solution.

Preparation and purification of 1-amino-2-phenoxy-4-hydroxyanthraquinone

A process for purifying indigo comprises stripping the as-synthesized aqueous alkaline indoxylate solution before its oxidation to indigo of impurities in the absence of oxygen by distillation or by passing in steam or an inert gas and then treating the indigo precipitated on oxidation of the stripped indoxylate solution with dilute hydrogen peroxide solution.

A process for the purification of indigo comprises treating the indigo with sulfuric acid to give indigo sulfate, separating off and subsequently hydrolyzing the latter to re-form indigo, and then treating the dye with dilute hydrogen peroxide solution.

A process for the preparation of purified indigo comprises extracting the aqueous alkaline indoxylate solution arising from the synthesis with an inert water-insoluble solvent in the absence of oxygen before oxidizing the indoxylate solution to give indigo.

Specific sulfonamidocarboxylic acids in the form of the alkali metal or alkanolamine salts are used as corrosion inhibitors in aqueous systems.

Use of salts of sulfonamidocarboxylic acids as corrosion inhibitors in

In a process for the manufacture of 2-amino-3-bromoanthraquinone by heating 2-aminoanthraquinone with bromine (in the molar ratio of 1:1) in sulfuric acid, while mixing, the improvement wherein crude 2-aminoanthraquinone, in sulfuric acid of from 60 to 90 percent strength by weight, which contains from 10 to 15% by weight of an alkanecarboxylic acid of 3 or 4 carbon atoms or a mixture of such acids, is heated with from 1 to 1.05 moles of bromine per mole of 2-aminoanthraquinone at from 130 to 150.degree. C. The 2-amino-3-bromoanthraquinone which is isolated may be used for the manufacture of dyes. It is at least as pure as that obtained from purified 2-aminoanthraquinone by the process of the prior art.

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Frankenthal, Germany

Reinhold Kohlhaupt