(A) Citraconic Anhydride.—Two hundred and fifty grams of itaconic anhydride (Note 1) is distilled rapidly at atmospheric pressure in a 500-cc. modified Claisen flask with a 15-cm. (6-in.) fractionating column (Note 2). The receivers for the distillate must be changed without interrupting the distillation. The distillate passing over below 200° consists of water and other decomposition products. The fraction which distils at 200–215° consists of citraconic anhydride and is collected separately. The yield is 170–180 g. (68–72 per cent of the theoretical amount) of a product melting at 5.5–6°. On redistillation under reduced pressure there is obtained 155–165 g. (62–66 per cent of the theoretical amount) of a product which boils at 105–110°/22 mm. and melts at 7–8° (Note 3).

(B) Citraconic Acid.—To 22.4 g. (0.2 mole) of pure citraconic anhydride in a 100-cc. beaker is added from a pipet exactly 4 cc. (0.22 mole) of distilled water. The mixture is stirred on a hot plate until a homogeneous solution is formed, then covered with a watch glass and allowed to stand for forty-eight hours. At the end of this time the mixture has solidified completely. The yield is 26 g. of a product melting at 87–89°. For further purification it is finely ground in a mortar, washed with 50 cc. of cold benzene, dried in the air, and then dried for twenty-four hours in a vacuum desiccator over phosphorus pentoxide. This furnishes 24.4 g. (94 per cent of the theoretical amount) of citraconic acid which melts at 92–93°.