A 5-l. three-necked flask is fitted with a mechanical stirrer, a reflux condenser, a thermometer, and an inlet tube extending to the bottom of the flask (Note 1). In the flask is placed a mixture of 238 g. (1.3 moles) of 2,4-dinitroaniline, 2.4 l. of 95% ethanol, and 1.2 l. of concentrated ammonium hydroxide (sp. gr. 0.90).

The mixture is heated to 45°, and with good stirring hydrogen sulfide is passed into the reaction mixture while its temperature is maintained between 45° and 55° (Note 2) and (Note 3). The yellow suspended particles of 2,4-dinitroaniline dissolve slowly to form an intensely red-colored solution. The reaction is complete when all the yellow particles have disappeared; reduction should be complete in 30–60 minutes (Note 4).

The reaction mixture is allowed to stand in an icebox for 16–18 hours to complete the separation of the product, which forms small, well-defined, deeply red-colored crystals. The 1,2-diamino-4-nitrobenzene is filtered by suction, washed with 150–250 ml. of cold water, and sucked dry on the funnel (Note 5).

The crude product is purified by dissolving it in a boiling mixture of 900 ml. of water and 110 ml. of concentrated hydrochloric acid (sp. gr. 1.19), and filtering the hot solution through a Norit bed using suction. The filter bed is washed with a boiling mixture of 90 ml. of water and 10 ml. of concentrated hydrochloric acid, and the washings are added to the main body of the solution. The filtered solution, while still hot, is treated with 100 ml. of concentrated ammonia (sp. gr. 0.90). The precipitated 1,2-diamino-4-nitrobenzene is filtered hot on a Büchner funnel, washed on the funnel with 150 ml. of water, and dried in an oven at 40–50°.

The purified material melts at 197–198° and weighs 105–115 g. (52–58%).