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Org. Synth. 1939, 19, 38
DOI: 10.15227/orgsyn.019.0038
DICHLOROACETIC ACID
[Acetic acid, dichloro-]
Submitted by Arthur C. Cope, John R. Clark, and Ralph Connor.
Checked by R. L. Shriner and Neil S. Moon.
1. Procedure
A solution of 250 g. (1.5 moles) of u.s.p. chloral hydrate in 450 cc. of warm water (50–60°) is placed in a 3-l. round-bottomed flask bearing a reflux condenser and thermometer (Note 1). The condenser is temporarily removed and 152.5 g. (1.52 moles) of precipitated calcium carbonate added; this is followed by 2 cc. of amyl alcohol (Note 2) and a solution of 10 g. of technical sodium cyanide in 25 cc. of water. Although the reaction is exothermic, the reaction mixture is heated with a low flame so that it reaches 75° in about ten minutes; at this point heating is discontinued. The temperature continues to rise to 80–85° during five to ten minutes and then drops. As soon as the temperature begins to fall the solution is heated to boiling and refluxed for twenty minutes. The mixture is then cooled to 0–5° in an ice bath, acidified with 215 cc. of concentrated hydrochloric acid (sp. gr. 1.18), and extracted with five 100-cc. portions of ether (Note 3). The combined ether extracts are dried with 20 g. of anhydrous sodium sulfate, the ether is removed by distillation from a steam bath, and the residue is distilled in vacuum from a Claisen flask with a fractionating side arm (Note 4). The yield of dichloroacetic acid, b.p. 99–104°/23 mm., is 172–180 g. (88–92 per cent of the theoretical amount) (Note 5).
2. Notes
1. The amount of hydrogen cyanide evolved is small, and the reaction may be carried out in a hood without any special device for removing this gas. The use of mechanical stirring does not improve the results.
2. Amyl alcohol is added to decrease the amount of foaming.
3. The emulsion which often forms during the ether extraction may be broken by filtering through a fluted filter or with suction.
4. The product decomposes when distilled at atmospheric pressure.
5. The preparation has been carried out with equally good results using double the quantities given above.
3. Discussion
Dichloroacetic acid has been prepared by the chlorination of acetic1 or chloroacetic2 acid, by hydrolysis of pentachloroethane,3 from trichloroacetic acid by electrolytic reduction4 or the action of copper,5 and by the action of alkali cyanides on chloral hydrate.6 The method described here is essentially that of Delépine.7

References and Notes
  1. Müller, Ann. 133, 159 (1865); Dow Chemical Company, U. S. pat. 1,921,717 [C. A. 27, 5084 (1933)].
  2. Maumené, Compt. rend. 59, 84 (1864).
  3. Alais, Froges, and Camargue, Fr. pat. 773, 623 [C. A. 29, 1437 (1935)].
  4. Brand, Ger. pat. 246,661 [C. A. 6, 2496 (1912)].
  5. Doughty and Black, J. Am. Chem. Soc. 47, 1091 (1925); Doughty and Derge, ibid. 53, 1594 (1931).
  6. Wallach, Ann. 173, 288 (1874); Pucher, J. Am. Chem. Soc. 42, 2251 (1920); Chattaway and Irving, J. Chem. Soc. 1929, 1038.
  7. Delépine, Bull. soc. chim. (4) 45, 827 (1929).

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

hydrochloric acid (7647-01-0)

ether (60-29-7)

sodium cyanide (143-33-9)

hydrogen cyanide (74-90-8)

sodium sulfate (7757-82-6)

copper (7440-50-8)

calcium carbonate (471-34-1)

chloral hydrate (302-17-0)

amyl alcohol (71-41-0)

dichloroacetic acid,
Acetic acid, dichloro- (79-43-6)

pentachloroethane (76-01-7)

trichloroacetic acid (76-03-9)