A
5-l. flat-bottomed flask, equipped with a
long (80–90 cm.) widebore condenser, a
separatory funnel, and a
mechanical stirrer (Note
1), is supported 10 cm. above an
electric hot plate.
Two grams of vanadium pentoxide (Note
2),
450 g. (4.2 moles) of sodium chlorate, and 1 l. of water are placed in the flask; the stirrer is started, the mixture is heated to 70–75° (Note
3), and about
5–10 cc. of 200 g. (2.06 moles) of furfural (Note
4) is added. As soon as a vigorous reaction starts the balance of the
furfural is added rapidly enough to maintain it (Note
5). The entire addition requires seventy to eighty minutes. Then the mixture is heated at 70–75°, with stirring, for ten to eleven hours and allowed to stand overnight at room temperature. The crude
fumaric acid is filtered with suction and dried in the air. It weighs
155–170 g. (
65–72 per cent of the theoretical amount) (Note
6).
More
fumaric acid may be obtained from the filtrate by heating it on the
water bath with
50 cc. of concentrated hydrochloric acid; the solution usually turns blue at the end of the reaction. The solution is concentrated to about 700 cc. and then cooled with running water. The
fumaric acid which separates is collected on a filter and dried in the air. It weighs
10–15 g. and melts at
282–284° in a
sealed tube.
The crude product is purified by recrystallization from about
1250 cc. of 1 N hydrochloric acid. This gives
100–110 g. of pure
fumaric acid, melting at
282–284° in a sealed tube. An additional amount of the acid may be obtained by concentrating the filtrate to a small volume on a water bath. The total yield of pure
fumaric acid is
120–138 g. (
50–58 per cent of the theoretical amount).