vogel_practical_ochem_3.pdf

194 PRACTICAL ORGANIC CHEMISTRY [II.
reflux condenser (protected by a drying tube containing soda lime), a
sealed stirrer (see Kyrides stirrer, Fig. //, 7, 10) and a dropping funnel,
are placed 23 g. of clean sodium and 150-200 ml. of sodium-dried xylene.
The flask is surrounded by an oil bath, which is heated until the sodium
has melted. The stirrer is started and, after the sodium is suitably
granulated, the oil bath is removed. When the contents of the flask have
cooled to the laboratory temperature, the stirrer is stopped. The xylene
may then be decanted, and the sodium washed with two 100 ml. portions
of sodium-dried ether to remove traces of xylene as in Method 1. Large
quantities of " molecular " sodium may be prepared by this method.
7. Sodium amalgam. The amalgam which is generally employed
for reductions contains from 1 to 3 per cent, of sodium. Amalgams with
a greater sodium content than 1*2 per cent, are solid at the ordinary
temperature and can be powdered in a mortar ; the 1 • 2 per cent, amalgam
is semi-solicl at room temperature but is completely fluid at 50°. Two
methods of preparation are available.
Method i. Nine grams of clean sodium are placed in a 500 ml. conical
flask and covered with 20 ml. of dry toluene. The sodium is cautiously
melted over a free flame, and the flame is extinguished. 750 g. of mercury
are added from a separatory funnel in drops with occasional shaking.
During the addition of the first 2-3 ml. of mercury the reaction is extremely
vigorous, but subsequently the rate of addition of the mercury
may be increased so that the toluene boils continuously. At the end of
the reaction, the toluene is allowed to evaporate completely ; if any
toluene remains, the excess should be decanted. The toluene vapour
remaining above the amalgam tends to protect it from the action of the
air. The resulting amalgam contains about 1-2 per cent, of sodium.
An amalgam of 2 per cent, strength can be prepared by this method
(15-2 g. of sodium in 750 g. of mercury) ; if all the toluene-has not
evaporated completely before the end of the reaction, it should be
decanted before the amalgam solidifies. If necessary, the amalgam is
melted on a hot plate and then poured on to a uralite or poilite board,
and then pulverised in a mortar * and transferred to a tightly stoppered
bottle. The preparation must be carried out in the fume cupboard since
mercury vapour is poisonous.
Method 2. The clean sodium (22-8 g.) is placed in a 500 ml. roundbottomed
three-necked flask, provided with a dropping funnel (containing
750 g. of mercury) in the central aperture and inlet and outlet tubes for
dry nitrogen in the two side apertures. The air is displaced by nitrogen.
About 10 ml. of mercury are added and the flask is warmed gently with a
free flame until the reaction commences. The flame is then removed and
the reaction is maintained by the slow addition of the mercury. When
about half the mercury has been introduced, the amalgam will commence
to solidify ; it should be kept molten by heating with occasional shaking.
After the addition of all the mercury, the hot molten amalgam is poured
on to a uralite or poilite board, powdered in a mortar and stored as in
Method 1. Amalgams of 1 and 2 per cent, strength may be prepared
similarly.
* The mortar should be provided with a tightly fitting rubber cover to protect the
powdered material from oxidation in air.