A.
p,α,α-Tribromoacetophenone. In a
1-l. three-necked flask (Note
1) equipped with an
efficient mechanical stirrer, a
dropping funnel, and a
gas outlet leading to a hood or trap are placed
100 g. (0.5 mole) of p-bromoacetophenone (Note
2) and
300 ml. of glacial acetic acid. The resulting solution is stirred and cooled to 20°, and a solution of
26 ml. (0.5 mole) of bromine in
100 ml. of glacial acetic acid is added dropwise (Note
3). Crystals of the mono-α-brominated derivative separate during the addition, which requires about 30 minutes. When the addition is completed, a second solution of
26 ml. (0.5 mole) of bromine in
100 ml. of glacial acetic acid is added dropwise. Slight heating may be necessary to keep the reaction proceeding, as indicated by decolorization of the
bromine, but the temperature should be kept as near 20° as possible. During the addition, which requires about 30 minutes, the solid dissolves and crystals of the di-α,α-brominated derivative appear toward the end of the addition. The flask is heated to dissolve the contents, which are transferred, preferably in a hood, to a
1-l. beaker and cooled rapidly by means of an
ice-water bath (Note
4). The mixture is filtered with suction (Note
5), and the solid is washed with
50% ethanol until colorless. The air-dried product has a slight pink cast and melts at
89–91°. The yield is
130–135 g. (
73–75%) (Note
6). A pure, white solid melting at
92–94° is obtained by recrystallization from
ethanol, but the initial product is sufficiently pure for the next step.