(
A)
Phosphorus Pentachloride Method.—In a
2-l. round-bottomed flask is placed a mixture of
250 g. (1.2 moles) of finely divided phosphorus pentachloride and
450 g. (2.5 moles) of sodium benzenesulfonate which has previously been dried for three hours at 140°. The mixture is heated in an
oil bath at 170–180° (Note
1) for fifteen hours (Note
2). It is advisable to have a
reflux condenser attached to the flask, although very little active refluxing takes place. Every four hours during the heating period, the flask should be removed from the
oil bath, cooled for fifteen minutes, stoppered and shaken thoroughly until the mass becomes pasty (sometimes ten to fifteen minutes are required to accomplish this). At the end of the heating period, the mixture is cooled and 1 l. of water with 1 kg. of cracked ice are added.
Benzenesulfonyl chloride sinks to the bottom, is separated, washed once with water, filtered if necessary, and distilled under reduced pressure for purification. The forerun, consisting of a little
chlorobenzene, water, and a little
benzenesulfonyl chloride, is discarded and the fraction boiling between
145–150° /45 mm. is collected. This weighs
330–360 g. (
75–80 per cent of the theoretical amount) (Note
3).