IN a 5-l. round-bottom flask (Pyrex) is placed a mixture of 500 g.
of phthalic anhydride and 400 g. of 28 per cent ammonium hydroxide.
The flask is fitted with an air condenser not less than 10 mm.
in diameter and is then slowly heated with a free flame until the mixture
is in a state of quiet fusion at a temperature of about 300'0. It
requires about one hour before all the water has gone and about
one and a half to two hours before the temperature of the reaction
mixture reaches 300'0 and the mixture is a homogeneous melt.
It is advisable, during the heating, to shake the flask occasionally;
some material sublimes into the condenser and must be pushed
down with a glass rod. The hot reaction mixture is now poured out
into a crock, covered with a paper to prevent loss by sublimation,
and allowed to cool. The product is practically pure without
further treatment, and melts at 232-235'0. The yield is 470-480 g.
(94-95 per cent of the theoretical amount).
Phthalimide may also be made by using 500 g. of phthalic anhydride
and 500 g. of ammonium carbonate which has been previously ground
in a mortar. The subsequent procedure is the same as when aqueous
ammonia is used. Frequent shaking is necessary, and the sublimed
material must be occasionally pushed back into the reaction flask.
About two hours are required for completion.