In a
3-l. three-necked round-bottomed flask fitted with an
effective mechanical stirrer, a
dropping funnel, and a
thermometer, and surrounded by an
ice bath, is placed
1270 ml. (23.0 moles) of concentrated sulfuric acid (sp. gr. 1.84). Then
363 g. (3.0 moles) of dimethylaniline (Note
1) is slowly added with stirring and cooling so that the temperature remains below 25°. Stirring and cooling are continued until the temperature falls to 5°. A nitrating mixture is prepared by adding
366 g. (200 ml., 3.6 moles) of concentrated sulfuric acid (sp. gr. 1.84) to
286 g. (200 ml., 3.15 moles) of concentrated nitric acid (sp. gr. 1.42), with cooling and stirring. This is placed in the dropping funnel and added, drop by drop, the end of the dropping funnel being kept beneath the surface of the solution of
dimethylaniline sulfate. The temperature is regulated between 5° and 10°, best by addition of small pieces of Dry Ice (Note
2); about 1.5 hours is required (Note
3). When the addition has been completed, the solution is stirred at 5–10° for 1 hour, and then poured, with stirring (Note
4), into an enameled pail containing 6 l. of ice and water (Note
5). Concentrated
ammonium hydroxide is added slowly, with good stirring and using a dropping funnel that extends beneath the surface of the liquid, until the color of the precipitate changes to a light orange (Note
6). During this step the temperature is kept below 25°, using Dry Ice. From
1900 to 2050 ml. of ammonium hydroxide is required. The crude
p-nitrodimethylaniline is collected on a filter and washed with 200 ml. of water (Note
7). Concentrated
ammonium hydroxide (sp. gr. 0.90) is again added to the combined filtrate and washings, with good agitation and cooling to keep the temperature below 25°, until the liquid gives a purple color on Congo red paper (Note
8). From
1500 to 1650 ml. of ammonium hydroxide is required. The product is collected on a
Büchner funnel and washed with 500 ml. of water. The crude
m-nitrodimethylaniline (
316–342 g. dry weight) is recrystallized from
400 ml. of hot 95% ethanol and carefully washed on the filter with
100 ml. of cold 95% ethanol. The yield is
280–316 g. (
56–63%) of bright orange crystals that melt at
59–60°.