In a 5-l. round-bottomed flask are placed 1.6 l. of water, 800 ml. of concentrated nitric acid (sp. gr. 1.42), and 400 ml. (364 g., 3 moles) of commercial 90% o-xylene (Note 1). A reflux condenser (40 cm. or longer) is fitted to the flask with a cork, and a gas-absorption trap is attached to the top of the condenser. The mixture is refluxed by heating in an oil bath kept between 145° and 155° for 55 hours (Note 2). At the end of this time the organic layer has settled to the bottom of the flask. The hot reaction mixture is poured with stirring into 1 kg. of ice in a 4-l. beaker. After cooling, the solid product is filtered, suspended in 2 l. of cold water, and filtered again. The wet product is dissolved by warming in 1 l. of 10% sodium hydroxide solution. After cooling, any unreacted xylene is separated by extraction with 250 ml. of ether. The aqueous layer is then heated on the steam bath with 5–10 g. of Norit and filtered hot with suction through a layer of Norit. The warm, clear red alkaline solution is added with vigorous mechanical stirring to 225 ml. of concentrated hydrochloric acid. The product is filtered from the warm solution, washed with cold water, and sucked as dry as possible on a Büchner funnel (Note 3).

The crude product is dissolved in 350 ml. of 95% ethanol and heated on the steam bath with 5 g. of Darco for 1 hour. The hot solution is filtered by gravity through a heated funnel. The filter paper is heated with an additional 70-ml. portion of 95% ethanol, and the mixture is filtered hot through a fresh paper, into the main solution. To the ethanolic solution, adjusted to a temperature of 55–60°, is added 480 ml. of warm (55–60°) water. After being cooled first to room temperature and then to ice-bath temperature, the crystallized product is filtered, washed with 250 ml. of cold 50% ethanol, and dried (Note 4). The yield of light-tan product melting at 99–101° amounts to 218–225 g. (53–55%) (Note 5) and (Note 6).