Ciba-geigy Ag

Johann Regli

Tibor Somlo

A process for the preparation of pure bromoanthraquinones by denitrobrominating corresponding nitroanthraquinones is described. The process comprises treating nitroanthraquinones of the formula I ##STR1## wherein X is hydroxy, mercapto, carboxy or halogen and m is 1, 2, 3 or 4 and n is 1 or 2, in the temperature range from 200.degree. to 350.degree. C. Bromoanthraquinones of more than 95% purity are valuable starting materials for dye synthesis and can be used directly without further purification.

Process for the preparation of bromoanthraquinones

A process for purifying crude monochloro- or monobromoanthraquinone is described. In this process, monochloro- or monobromoanthraquinone which contains by-products as impurities is mixed with a hot non-polar aliphatic solvent in such a ratio that more than half of the crude product goes into solution and the remainder which contains the impurities forms a second lower phase, said eutectic melt is separated, and the saturated solution is allowed to cool, and the monochloro- or monobromoanthraquinone, which precipitates in pure form, is isolated.

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Birsfelden, Switzerland

Johann Regli