B.
Fumaronitrile. The dry, finely powdered amide (Note
5)
(228 g., 2.0 moles) and
613 g. (4.3 moles) of phosphorus pentoxide are placed in a
3-l. flask and thoroughly mixed by shaking. The flask is connected to a
1-l. suction flask receiver by means of a short 17-mm. i.d. 60° elbow extending about 15 cm. into the receiver. The receiver is cooled by immersion in an
ice bath or by cold running water. The system is evacuated to 15–30 mm. by means of a
water aspirator. The flask is then heated with one or two burners, using large soft flames. Heating should be started at the side and moved toward the bottom as the reaction progresses (Note
6). The reaction mass froths and blackens, and the product distils and sublimes into the receiver. The elbow leading to the receiver must be heated occasionally to melt condensed
fumaronitrile. Heating is continued until no more
fumaronitrile distils from the reaction flask (1.5 to 2 hours) (Note
7). The product, usually white and sufficiently pure (m.p.
93–95°) for most purposes, is obtained in a yield of
125–132 g. (
80–85%). The product is recrystallized conveniently (in a
fume hood) by dissolving it in
150 ml. of hot benzene and decanting or filtering the solution into
500 ml. of hexane or petroleum ether (Note
8) and (Note
9). The yield of long, glistening prisms, m.p.
96°, amounts to
117–125 g. (
75–80%).