Process for separating 1,5-dinitroanthraquinone and 1,8-dinitroanthraquinone from dinitroanthraquinone mixtures

A process for separating substantially pure 1,5-dinitroanthraquinone and substantially pure 1,8-dinitroanthraquinone from an anthraquinone dinitration mixture containing 1,5- and 1,8-dinitroanthraquinone which consists essentially of adding to the dinitration mixtures with a mixture of concentrated nitric acid and an inert organic solvent, said inert organic solvent being an aliphatic or cycloaliphatic hydrocarbon having up to 12 carbon atoms which can be substituted once or several times by halogen or by a nitro group, separating off the insoluble 1,5-dinitroanthraquinone from the resulting mixture and isolating the 1,8-dinitroanthraquinone from the resulting mother liquor.