In a
1-l. three-necked flask having ground-glass joints are placed
500 g. (569 ml., 4.72 moles) of o-xylene,
12 g. of clean iron filings, and a crystal of
iodine (Note
1). The flask is fitted with a
dropping funnel, a
stirrer (Note
2), and a
condenser; a
thermometer is suspended through the condenser on a
platinum or Nichrome wire and arranged so that the bulb extends beneath the surface of the liquid. The top of the condenser is connected to a
gas-absorption trap. The mixture is stirred and cooled in an ice-salt mixture, preferably under a
hood.
Six hundred and sixty grams (4.13 moles) of bromine is added drop-wise over a 3-hour period; during this time the internal temperature is maintained at 0° to −5° (Note
3). After all the
bromine has been added the reaction mixture is allowed to stand overnight. It is poured into water and washed successively with a 500-ml. portion of water, two
500-ml. portions of 3% sodium hydroxide solution (Note
4), and one 500-ml. portion of water. The product is then steam-distilled; about 8 l. of distillate is collected (Note
5). The organic layer is separated from the water and dried over
calcium chloride. The
4-bromo-o-xylene is distilled through a
short column under reduced pressure, and the fraction boiling at
92–94°/14–15 mm. (
n22D 1.5558) is collected. The yield is
720–745 g. (
94–97%, based on
bromine) (Note
6).