Organic Syntheses, Coll. Vol. 2, p.181 (1943); Vol. 19, p.38 (1939).
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.
per cent of the theoretical amount) (Note 5)
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.
The emulsion which often forms during the ether
extraction may be broken by filtering through a fluted filter or with suction
The product decomposes when distilled at atmospheric pressure.
The preparation has been carried out with equally good results using double the quantities given above.
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