Organic Syntheses Procedure

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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.

Working with Hazardous Chemicals

The procedures in Organic Syntheses are intended for use only by persons with proper training in experimental organic chemistry. All hazardous materials should be handled using the standard procedures for work with chemicals described in references such as "Prudent Practices in the Laboratory" (The National Academies Press, Washington, D.C., 2011; the full text can be accessed free of charge at http://www.nap.edu/catalog.php?record_id=12654). All chemical waste should be disposed of in accordance with local regulations. For general guidelines for the management of chemical waste, see Chapter 8 of Prudent Practices.

In some articles in Organic Syntheses, chemical-specific hazards are highlighted in red "Caution Notes" within a procedure. It is important to recognize that the absence of a caution note does not imply that no significant hazards are associated with the chemicals involved in that procedure. Prior to performing a reaction, a thorough risk assessment should be carried out that includes a review of the potential hazards associated with each chemical and experimental operation on the scale that is planned for the procedure. Guidelines for carrying out a risk assessment and for analyzing the hazards associated with chemicals can be found in Chapter 4 of Prudent Practices.

The procedures described in Organic Syntheses are provided as published and are conducted at one's own risk. Organic Syntheses, Inc., its Editors, and its Board of Directors do not warrant or guarantee the safety of individuals using these procedures and hereby disclaim any liability for any injuries or damages claimed to have resulted from or related in any way to the procedures herein.

The paragraphs above were added in September, 2014. The statements above do not supersede any specific hazard caution notes and safety instructions included in the procedure.

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

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