Organic Syntheses, Coll. Vol. 2, p.88 (1943); Vol. 10, p.12 (1930).
A 5-l., three-necked, round-bottomed flask
is provided with an efficient mechanical stirrer
, a 48-cm. Allihn reflux condenser
, a thermometer
, and a 500-cc. separatory funnel
, the stem of which reaches nearly to the bottom of the flask (Note 1)
Through the separatory funnel are introduced 1.6 l. of water, 500 cc. of c. p. acetone
, and 372 cc. of glacial acetic acid
. The stirrer is started and the temperature of the water bath
is raised to 70–80°, so that the mixture in the flask is at about 65° (Note 2)
. Then 354 cc. (7.3 moles) of bromine
is carefully added through the separatory funnel. The addition, which requires one to two hours, is so regulated as to prevent the accumulation of unreacted bromine (Note 3)
. As a rule the solution is decolorized in about twenty minutes after the bromine
has been added. When the solution is decolorized, it is diluted with 800 cc. of cold water, cooled to 10°, made neutral to Congo red
with about 1 kg. of solid anhydrous sodium carbonate
, and the oil which separates is collected in a separatory funnel and dried with 80 g. of anhydrous calcium chloride
. After drying, the oil is fractionated and the fraction boiling at 38–48°/13 mm.
is collected. The yield is 470–480 g.
per cent of the theoretical amount). It may be used without further purification for the preparation of acetol (p. 5)
; but, if a purer product is desired, the above product is refractionated and the fraction boiling at 40–42°/13 mm.
is collected. The yield is 400–410 g.
per cent of the theoretical amount).
The higher-boiling fraction contains a mixture of isomeric dibromoacetones.
The apparatus should be set up with the flask in a large container
(such as a 14-qt. galvanized pail
) to be used as a water bath, and under a well-ventilated hood
, as both the bromine
are powerful irritants to the skin and mucous membranes.
It is necessary to warm the reaction mixture to this temperature to ensure a smooth reaction
It is not advisable to have too great an excess of bromine
present at any time, as it sometimes reacts suddenly with great violence.
A procedure similar to the one described above, except that the reaction mixture is illuminated with a powerful light, has been published.6
This preparation is referenced from:
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