Organic Syntheses, Coll. Vol. 3, p.788 (1955); Vol. 20, p.92 (1940).
. A 1-l. three-necked flask
is fitted with an oil-sealed mechanical stirrer
, a 500-ml. dropping funnel
, and a reflux condenser
, the top of which is connected to a gas-absorption trap
. A 300-watt tungsten lamp is clamped in such a position that its bulb is within 1 in. of the flask (Note 1)
. Into the flask is introduced 100 g. (0.94 mole) of dry p-xylene
), and the flask is heated in an oil bath
maintained between 140° and 160°. The stirrer is started, and, when the xylene
starts boiling, 700 g. (224 ml., 4.38 moles) of dry bromine (Note 2)
is gradually added through the dropping funnel at such a rate that there is never any large amount of unreacted bromine
in the flask. Stirring and heating are continued throughout the reaction, which requires 6–10 hours. After all the bromine
has reacted, the mixture is cooled and dissolved in 1 l. of warm chloroform
. The chloroform
solution is cooled in an ice bath
and the product removed by filtration. It is light gray, melts at 165–169°
, and weighs 250–258 g.
After a second recrystallization from 1 l. of chloroform
, 190–200 g.
of light-gray crystals melting at 168–170°
is obtained. An additional 15–20 g.
may be obtained by concentrating the chloroform
filtrate to 250 ml. and recrystallizing the precipitate from fresh chloroform
. The total yield is 205–220 g.
. A 2-l. round-bottomed flask
is fitted with a still head, capillary ebullition tube, and receiver
in an assembly for a vacuum distillation. Into the flask are introduced 84.3 g. (0.2 mole) of finely powdered tetrabromo-p-xylene
and 200 ml. of concentrated sulfuric acid (95%)
. The reactants are thoroughly mixed by shaking. A vacuum is applied by means of a water pump
, and a stream of air is allowed to pass through the capillary tube in order to facilitate the rapid removal of hydrogen bromide
. The flask is heated in an oil bath to 70°, and, as the evolution of gas becomes less vigorous, the temperature of the bath is gradually raised to 110° (Note 3)
. The reaction is complete when a perfectly clear solution is obtained and no more gas is evolved (about 2.5 hours). The flask is then cooled and the contents are poured on 600 g. of crushed ice. The crystalline solid is collected on a filter, washed with a little water, and recrystallized from 600 ml. of 10% methanol
with the aid of 1 g. of decolorizing carbon
to remove the yellow color. The small amount of tetrabromoxylene
which remains undissolved is separated with the carbon
and washed on the filter with two 100-ml. portions of hot 10% methanol
. The yield of pure product, m.p. 115–116°
, is 21.7–22.5 g.
It is important to have light shining on the reaction mixture throughout the bromination. The bromination may also be accomplished by placing the flask in direct sunlight.
The mixture foams considerably and must be watched. The foaming can be controlled by raising the temperature slowly and regulating the vacuum. For this reason it is difficult to hydrolyze larger amounts of the tetrabromide.
This preparation is referenced from:
Chemical Abstracts Nomenclature (Collective Index Number);
sulfuric acid (7664-93-9)
phosphorus pentachloride (10026-13-8)
nitric acid (7697-37-2)
hydrogen bromide (10035-10-6)
lead nitrate (10099-74-8)
p-xylyleneglycol monoethyl ether
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