Bayer Aktiengesellschaft

Bernd Schroeder

Karl-Werner Thiem

Wolfgang Auge

Rutger Neeff

Rudolf Braden

Bernd Thelen

A process has been developed for isolating aromatic dinitro compounds by using nitric acid in specified concentrations in different portions of a rectifying column and separating off the mixture of aromatic dinitro compounds from the sump of the rectifying column.

Process for isolating aromatic dinitro compounds

Process for the preparation of 1-alkylamino-anthraquinones which comprises reacting 1-nitroanthraquinone with a monoalkylamine in the presence of an ether, a hydrocarbon or a mixture of an ether and a hydrocarbon. The 1-alkylamino-anthraquinones which are obtained can be employed directly as dyestuffs or used, without further purification, for the production of dyestuffs. Process of the invention results in the procurement of 1-alkylamine-anthraquinones of high purity and in high yield and avoids the formation of undesired by-products.

Process for the preparation of 1-alkylamino-anthraquinones

A mixture of dinitroanthraquinones of which at least 35% is 1,5-dinitroanthraquinone is dissolved at elevated temperature in a halogenated aromatic hydrocarbon, a carboxylic acid nitrile or a cyclic sulphone and is thereafter cooled selectively to precipitate substantially pure 1,5-dinitroanthraquinone. Preferred solvents are 1-chloronaphthalene, sulpholane and adipic acid dinitrile. The temperature of dissolution ranges from about 120.degree. C up to the boiling point and cooling is by about 10.degree. to 200.degree. C to a temperature not below about 0.degree. C.

Preparation of pure 1,5-dinitroanthraquinone

A mixture of dinitroanthraquinones of which at least 70% is 1,8-dinitroanthraquinone is dissolved at elevated temperature in a halogenated aromatic hydrocarbon, a carboxylic acid nitrile or a cyclic sulphone and is thereafter cooled selectively to precipitate substantially pure 1,8-dinitroanthraquinone. Preferred solvents are 1-chloronaphthalene, sulpholane and adipic acid dinitrile. The particular temperature of dissolution and cooling will depend upon the particular solvent.

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Odenthal, Germany

Bernd Schroeder