Organic Syntheses, CV 2, 181
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.
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
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