In a
5-l. round-bottomed flask, fitted with a
liquid-sealed mechanical stirrer, a
dropping funnel, and a
tube leading to a gas trap to carry off the
hydrogen bromide,
278 g. (2 moles) of p-nitrophenol (m.p.
112–113°) is dissolved in
830 cc. of glacial acetic acid. To this solution at room temperature is added, dropwise with stirring during the course of three hours, a solution of
750 g. (240 cc., 4.7 moles) of bromine in
700 cc. of glacial acetic acid. After the addition of the
bromine the reaction mixture is stirred for one-half hour and then warmed on the
steam bath (internal temperature about 85°) for one hour in order to remove as much of the excess
bromine as possible. The last traces of
bromine are removed by passing a stream of air into the reaction mixture, which then has a yellow or brown color. The mixture is treated with 1.1 l. of cold water, stirred until cool (Note
1), and allowed to stand in ice, or in an ice chest, overnight. The pale yellow crystalline product is collected on a
19-cm. Büchner funnel and washed first with
500 cc. of 50 per cent aqueous acetic acid and then thoroughly with water. It is dried in an
oven at 40–60° or in a
vacuum desiccator over
sodium hydroxide. The yield is
570–583 g. (
96–98 per cent of the theoretical amount) of a nearly colorless product melting with decomposition at
138–140° (Note
2).