A.
α,α,α',α'-Tetrabromo-p-xylene. 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 (m.p.
11–12°), 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. (
51–55%).