vogel_practical_ochem_3.pdf

63] AROMATIC COMPOUNDS 605
white product may be obtained by the following chromatographic procedure
(see Section 11,46). Dissolve 100 g. of the coloured compound in
350 ml. of tt-hexane and pass the solution through a 3-4" column of activated
alumina (80-200 mesh); wash the column with 300 ml. of w-hexane.
Remove the w-hexane by distillation : 98 g. of pure /J-bromonaphthalene,
m.p. 58°, remains. This is sufficiently pure for use in Grignard reactions.
IV,63. m-BROMOTOLUENE
* The successive stages in the preparation are as follows :—
p-Acetotoluidide and m-bromo-p-acetotoluidide (3-bromo-4acetaminotoluene).
Prepare a solution of ^-acetotoluidide in glacial
acetic acid by boiling 107 g. of jp-toluidine with 400 ml. of glacial acetic
acid in a 1-litre round-bottomed flask, provided with a reflux condenser,
for 2 hours. Remove the reflux condenser, replace it by a mechanical
stirrer, and stir the solution vigorously ; some jt>-acetotoluidide may
separate as small crystals as the temperature falls (1). When the temperature
has fallen to about 45°, add 162-5 g. (51 ml.) of bromine from a
separatory funnel at such a rate that the temperature of the well-stirred
mixture is maintained at 50-55°. A precipitate may separate during the
addition which requires 30-40 minutes, but this dissolves later. Continue
the stirring for a further 30 minutes after all the bromine has been added.
Then pour the reaction mixture in a thin stream into a well-stirred mixture
of 1 kilo of crushed ice and 1 kilo of water to which 14 g. of solid sodium
bisulphite has been added. If the colour of the bromine persists, add
a little more sodium bisulphite. Filter the crystalline 3-bromo-4acetaminotoluene
with suction on a Buchner funnel, wash thoroughly with
water and press well. Dry in the air until the weight does not exceed
250 g. (2) ; further purification is unnecessary before proceeding to the
next stage.
3-Bromo-4-aminotoluene hydrochloride. Transfer the partially
dried 3-bromo-4-acetaminotoluene to a 1-5-litre round-bottomed flask,
add 250 ml. of rectified spirit, and reflux on a water bath until the solid
dissolves completely. Introduce through the condenser 250 ml. of concentrated
hydrochloric acid to the boiling solution and continue the
refluxing for a further 3 hours. During this time crystals of 3-bromo-4aminotoluene
hydrochloride separate. Pour the hot mixture into a 1-litre
beaker and cool thoroughly. Filter the crystals of the hydrochloride at
the pump through a Buchner funnel and wash rapidly with two 50 ml.
portions of chilled rectified spirit. The yield of the hydrochloride is 150 g.
3-Bromo-4-aminotoluene. Suspend the hydrochloride in 400 ml.
of water in a 1-litre beaker equipped with a mechanical stirrer. Add a
solution of 70 g. of sodium hydroxide in 350 ml. of water. The free base
separates as a dark heavy oil. After cooling to 15-20°, transfer the mixture
to a separatory funnel and run off the crude 3-bromo-4-aminotoluene.
This weighs 125 g. and can be used directly in the next step (3).
m-Bromotoluene. To a cold mixture of 400 ml. of rectified spirit
and 100 ml. of concentrated sulphuric acid contained in a 2-5-litre roundbottomed
flask, provided with an efficient mechanical stirrer, add 125 g.
of crude 3-bromo-4-aminotoluene. Stir the solution and cool to 5°;