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).