Process for the preparation of 1-nitro-anthraquinone which is practically free of 1,5-dinitro-anthraquinone

In a known process for the purification of 1-nitro-anthraquinone by isolating 1-nitro-anthraquinone from an impure composition containing anthraquinone nitration products and reactants primarily containing 1-nitro-anthraquinone and containing as an impurity 1,5-dinitro-anthraquinone, the improvement comprising removing 1,5-dinitro-anthraquinone by adding to said composition a mixture of concentrated nitric acid, containing at least 75% by weight HNO.sub.3 and not more than 25% by weight H.sub.2 O and an inert organic solvent which is miscible with the concentrated nitric acid and is selected from the group consisting of aliphatic and alicyclic hydrocarbons with up to 12 carbon atoms, and halogen derivatives thereof, wherein the relative quantities of nitric acid and inert organic solvent in said mixture as well as the total quantities in said composition, are such that the solubility of 1-nitroanthraquinone and anthraquinone in the mixture of nitric acid and organic solvent is greater that the sum of the partial solubilities in the individual components of the solvent mixture and subsequently, the undissolved 1,5-dinitro-anthraquinone containing constitutent is separated from the solution thus formed.