202 ACID CHLORIDES.
Sulphuric acid mono-chloride can be prepared in still another way by the
direct addition of hydrogen chloride to sulphur trioxide:
SO 3 + HC1 = HO.SO 2 C1.
All acid chlorides have a choking, often very disagreeable odor, and all
fume when exposed to moist air. In preparing them, moisture must be
excluded with great care.
Sulphuryl Chloride. Connect in series a 500-c.c. distilling flask,
a fairly long condenser, and a receiving flask, making all the joints
tight with closely fitting cork stoppers. From the receiver lead
an escape-tube to the ventilating flue. Through the cork in the
neck of the distilling flask pass two tubes, reaching to the bottom
of the flask, by means of which sulphur dioxide and chlorine can
be introduced separately. Allow the distilling flask to rest in a
porcelain dish on a water-bath, which is not heated at the start.
Place 50 g. of camphor in the distilling flask and fill the porce-
lain dish wth water and a few pieces of ice. Generate sulphur
dioxide from 400 g. of copper turnings and 800 g. of concentrated
sulphuric acid (or from bisulphite solution, see note, p. 71).
Pass the gas first through a sulphuric acid wash bottle and then
into the distilling flask, where it is taken up by the camphor, with
which it forms a colorless liquid. Then begin to introduce chlorine,
which is likewise dried by sulphuric acid (cf. No. 42, p. 69).
Regulate the evolution of the two gases so that about equal
amounts of each bubble through the washing bottles; an excess of
chlorine colors the contents of the distilling flask yellow. Con-
tinue the process until this flask is a little more than half filled.
Towards the end allow first an excess of chlorine to collect in the
flask and then strengthen the stream of sulphur dioxide until this
excess is just removed, after which stop the evolution of the gases.
After some time — six to twelve hours — remove the porcelain
dish and heat the flask on the water-bath as long as anything
distils over; at first a considerable quantity of gas is evolved. If
the distillate contains free chlorine remove it by shaking the
liquid with mercury (cf. Nos. 51 and 52), and filtering through
a perfectly dry asbestos felt in a Gooch crucible. Finally redistil
the material from a distilling flask provided with a thermometer
and a condenser. Boiling-point, 69.5°.
A mixture of a few drops of sulphuryl chloride and a few c.c. of
water reacts slowly with the formation of sulphuric and hydro-