Concentrated sulfuric acid (160 ml.) is placed in a 1-l. three-necked flask fitted with a glass stirrer and a thermometer, and 15.2 g. (0.22 mole) of solid sodium nitrite is added over a period of 10–15 minutes with stirring. After the addition is completed, the temperature is raised to 70° and the mixture is stirred until all the sodium nitrite dissolves. The solution is cooled to 25–30° with an ice bath, and a solution of 36.6 g. (0.2 mole) of 2,6-di-nitroaniline (p.364) in 400 ml. of hot glacial acetic acid is added slowly, with stirring, at such a rate that the temperature remains below 40° (Note 1). After the addition is completed, the solution is stirred at 40° for 0.5 hour. A solution of 44 g. (0.44 mole) of cuprous chloride in 400 ml. of concentrated hydrochloric acid is prepared in a 2-l. beaker and cooled in an ice bath, and the solution of the diazonium salt is added in portions over a period of about 5 minutes, with manual stirring, at a rate which keeps the effervescence from becoming too vigorous. The mixture becomes hot during the addition, and it is stirred intermittently while being cooled in an ice bath until the effervescence slackens. It is then heated on a steam bath with occasional stirring until the temperature reaches 80°. After about 20 minutes at that temperature the effervescence ceases, and then an equal volume of water is added and the mixture is cooled in an ice bath. After several hours the yellow, crystalline 1-chloro-2,6-dinitrobenzene is collected on a suction filter, washed with water, and dried (Note 2). The product, which is sufficiently pure for most purposes without recrystallization, is obtained in a yield of 28.7–30 g. (71–74%); m.p. 86–88°. The product can be recrystallized from 90% (by volume) acetic acid (2 ml. per g.) or by dissolving it in hot benzene (1.5 ml. per g.) and adding petroleum ether (3 ml. per g.); m.p. 86–87°.