Org. Synth. 1931, 11, 28
DOI: 10.15227/orgsyn.011.0028
Submitted by R. L. Shriner, S. G. Ford, and L. J. Roll.
Checked by C. R. Noller
1. Procedure
(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°.
2. Notes
1. The crude itaconic anhydride obtained as described on p. 368 was used. Itaconic acid may be substituted for the anhydride.
2. The success of the preparation depends upon a rapid distillation and changing the receivers without interrupting the distillation. The best yields are obtained when the heating period is of short duration.
3. The crude citraconic anhydride contains a small amount of water, acetone, and citraconic acid. Vacuum distillation allows the removal of these impurities without materially decreasing the yield.
3. Discussion
Citraconic anhydride has been prepared by the distillation of citraconic acid and of citric acid.1
Citraconic acid has been obtained by distillation of citric acid,2 of lactic acid,3 and of hydroxypyrotartaric acid;4 and by treating citric acid with hydriodic acid.5 A mixture of citraconic and itaconic acids is obtained by flowing a concentrated aqueous solution of citric acid into a heated evacuated vessel, distilling under reduced pressure the mixture of anhydrides formed, and allowing the mixture to react with water.6
This preparation is referenced from:

References and Notes
  1. Anschütz, Ber. 14, 2788 (1881).
  2. Crasso, Ann. 34, 68 (1840); Kekulé, "Lehrbuch der organischen Chemie," 2, 317 (1866); Wilm, Ann. 141, 28 (1867).
  3. Engelhardt, ibid. 70, 243, 246 (1849).
  4. Demarçay, Ber. 9, 963 (1876).
  5. Kämmerer, Ann. 139, 269 (1866).
  6. Boehringer Sohn A.-G., Brit. pat. 452,460 [C. A. 31, 1045 (1937)].

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

citraconic and itaconic acids

Benzene (71-43-2)

citric acid (77-92-9)

acetone (67-64-1)

hydriodic acid (10034-85-2)

Citraconic anhydride (616-02-4)

Citraconic acid (498-23-7)

Itaconic anhydride (2170-03-8)

Itaconic acid (97-65-4)

lactic acid (50-21-5)

hydroxypyrotartaric acid

phosphorus pentoxide (1314-56-3)