Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

CATALYTIC HYDKOGBNATION 377
the sleeve is pushed and thus maintains stability. By means of
a thick-walled rubber tube carrying a spring clip the glass tube
is directly connected to the gas-holder.
of the latter is fixed in a large
condenser clamp.
Before hydrogenation is begun
The measuring cylinder
the whole apparatus is tested for gas-tightness
as follows: The opening at the side of the bulb
is closed, and by turning the cocks A and
B the gas-holder is provisionally filled with
hydrogen. After closing the cocks the level
of the water in the cylinder is marked
while it is at the same height as that of the
water in the container, and the empty bulb
is shaken for a quarter of an hour. If the
level is unchanged after this period (with
unaltered room temperature)
can proceed.
hydrogenation
FIG. 58
0-5 g. of palladium on charcoal (see p. 378) is put into the dry
bulb (which still is full of air) and a solution of 5 g. of cinnaniic
acid in 30 c.c. of 80 per cent methyl alcohol is cautiously
added. The catalyst must be completely covered by the solution—
an explosion may occur when hydrogen is admitted if traces of the
catalyst remain fixed to the walls of the bulb. The cock B is closed,
A is opened, and hydrogen (washed with potassium permanganate
solution) is passed in from a cylinder until all the air has been displaced
from bulb and tubes. Previously the gas-holder (capacity
1 litre) and the tubes to the cock B have been filled with water,
which is now driven out by hydrogen after A has been closed, B
opened, and the water container lowered. The side opening is
now closed, the hydrogen cylinder (or Kipp) is disconnected, the
level of the liquid read as when testing for gas-tightness, and the
shaking apparatus is set in motion. 1 The container stands on the
gas-holder so that a slight pressure is maintained.
Although the amount of catalyst used here is very small (about
15 mg. of Pd), sufficient hydrogen to saturate the ethylene double
1 If it ia neceaaary to refill the gas-holder during the experiment owing to conaumption
of gas, the cylinder ia connected to A, the clip on the connecting rubber
tubing of the horizontal tube of the bulb ia acrewed down, the cocks A and B are
opened, and hydrogen ia carefully passed in.