1604-43-9

A process has been invented for the isolation of 1,6- and 1,7-dinitroanthraquinone by treating mixtures containing these isomers with nitrobenzene.

Substantially pure 1,5- and/or 1,8-dinitroanthraquinone is recovered from dinitration mixtures which may contain sulfuric acid or a perfluoralkane sulfonic acid by adjusting the nitric acid concentration in the nitration mixture to a value of 91 to 96% for a ratio by weight of nitric acid to solids of from 2.5 : 1 to 10 : 1; separating off the insoluble crude 1,5-dinitroanthranthraquinone at 15° to 50°C; taking up the 1,5-dinitroanthraquinone with 90 to 100% nitric acid in a ratio by weight of nitric acid to solids of from 0.5 : 1 to 3.5 : 1; stirring at 15° to 80° C; separating off the insoluble pure 1,5-dinitroanthraquinone thus obtained; adjusting the mother liquid left following separation of the crude 1,5-dinitroanthraquinone to a nitric acid concentration of from 88 to 94% for a ratio by weight of nitric acid to solids of from 3.0 : 1 to 12 : 1, with the proviso that the nitric acid concentration is at least 1.5% lower than in the preceding separation of crude 1,5-dinitroanthraquinone; and separating off the pure 1,8-dinitroanthraquinone obtained in this way at a temperature in the range of from 20° to 50°C and freeing it from the nitric acid adhering thereto.