Process for preparing highly pure 1-nitroanthraquinone

#This invention pertains to a process for the preparation of 1-nitroanthraquinone and to a novel intermediate suitable for the preparation thereof. More particularly, this invention pertains to a process for preparing 1-nitroanthraquinone from 3-nitro-o-xylene via the novel intermediate 2-methyl-3-nitrobenzophenone.

#The compound 1-nitroanthraquinone, and its reduction product 1-aminoanthraquinone, are important intermediates in the preparation of pigments, vat dyes, disperse dyes and acid dyes. Currently, 1-aminoanthraquinone is manufactured by either nitrating anthraquinone and reducing the nitration product, or sulfonating anthraquinone and aminating the sulfonation product.

#The product obtained by the nitration process is accompanied by 2-nitroanthraquinone and 1,5-, 1,8-, 1,6-, and 1,7-dinitroanthraquinone, undesirable contaminants. In order to obtain high quality 1-aminoanthraquinone from this product, multiple purification steps are required after the nitration and reduction reactions.

#The following example is illustrative of the process of this invention. All percentages mentioned in the example are by weight unless otherwise indicated.

#A mixture of 3-nitro-o-xylene (15.1 grams; 0.10 mole) in a 51.6% aqueous solution of nitric acid, prepared by gradually adding 75 mls. of concentrated nitric acid to 38 mls. of water, was stirred and heated at reflux for 24 hours and then cooled to room temperature. The reaction mixture was filtered to separate the precipitate. The filtrate was extracted with chloroform, allowed to settle and the chloroform layer separated therefrom. The chloroform layer was extracted with aqueous sodium carbonate and the aqueous phase was separated from the organic phase. The organic phase was then concentrated to dryness to recover unreacted 3-nitro-o-xylene (6.5 grams; 0.043 mole).

#The solid precipitate was added to the aqueous phase and the resulting mixture was stirred until the solid dissolved completely. The resulting solution was then acidified by adding concentrated hydrochloric acid thereto. The resulting white precipitate was separated by filtration, washed with water and dried to obtain 4.8 grams of product which was identified by its infrared spectrum as 2-methyl-3-nitrobenzoic acid. The yield based on 3-nitro-o-xylene consumed was 46.6%.