In a
3-l. round-bottomed flask fitted with a small glass paddle stirrer and a reflux condenser are placed
101 g. (0.4 mole) of β-methyl-β-phenyl-α,α'-dicyanoglutarimide (
p. 662), and a mixture of 500 ml. of water,
500 g. of concentrated sulfuric acid, and
400 ml. of glacial acetic acid. Without starting the stirrer (Note
1), the mixture is heated under reflux for 2 hours. Then the stirrer is cautiously started, and reflux is continued for a total of 80 hours. The reaction mixture is transferred to a
6-l. Erlenmeyer flask, 3 l. of water is added and the mixture cooled in a
refrigerator overnight. The precipitated acid is filtered by suction (Note
2), washed with 100 ml. of water, and air-dried to constant weight. The crude, dry product is swirled for 5 minutes with
200 ml. of benzene, filtered by suction, washed with two
100-ml. portions of benzene, and again air-dried. The yield of acid, m.p.
136–140°, is
64.5–68 g. (
72.5–76.5%) (Note
3) and (Note
4).