Org. Synth. 1939, 19, 24
Submitted by R. M. Cowper and L. H. Davidson.
Checked by Lee Irvin Smith and E. W. Kaiser.
A solution of 50 g. (0.42 mole) of acetophenone (Org. Syn. Coll. Vol. I, 1941, 111)
in 50 cc. of pure anhydrous ether (Note 1)
is placed in a dry three-necked flask
fitted with a separatory funnel
, mechanical stirrer
, and reflux condenser (Note 2)
. The solution is cooled in an ice bath
, 0.5 g. of anhydrous aluminum chloride
is introduced (Note 3)
, and 67 g. (21.5 cc., 0.42 mole) of bromine
is added gradually from the separatory funnel, with stirring, at the rate of about 1 cc. per minute. The bromine
color disappears rapidly although very little hydrogen bromide
is evolved; towards the end of the reaction the solution becomes pink.
After the bromine has been added the ether and dissolved hydrogen bromide are removed at once (Note 4) under reduced pressure with a slight current of air. The phenacyl bromide remains as a solid mass of brownish yellow crystals (Note 5); the color is removed by shaking with a mixture of 10 cc. of water and 10 cc. of petroleum ether. The crystals are filtered with suction and washed several times with fresh portions of the solvent mixture, if necessary, until a white product is obtained (Note 6). The crude phenacyl bromide weighs 74–80 g. (88–96 per cent of the theoretical amount) and melts at 45–48°. This material is sufficiently pure for many purposes. If higher purity is desired the crude product may be recrystallized from 25–30 cc. of methanol, yielding 54–55 g. (64–66 per cent of the theoretical amount) of white crystals melting at 49–51° (Note 7).
Dry carbon tetrachloride
may be used as a solvent but is less favorable than dry ether
Quantities up to 200 g. of acetophenone
may be brominated in a single operation with equally good yields but this is not generally advisable unless the product is to be used at once, since it becomes discolored on standing.
Without aluminum chloride
the reaction is slow and incomplete.
If the ether
and hydrogen bromide
are not removed immediately the solution blackens on standing and a lower yield of less pure product results.
is a lachrymator and should be manipulated carefully, to avoid contact with the skin and inhalation of the vapor.
The water removes yellow color due to residual hydrogen bromide
, and the petroleum ether
removes unchanged acetophenone
or oily by-product. Since the product is quite insoluble in water and only slightly soluble in cold petroleum ether
, it may be washed several times with little loss.
The checkers observed that all specimens of the product, even after recrystallization, although white at first, became dark and discolored on standing in a vacuum desiccator
over calcium chloride
has been prepared by the bromination of acetophenone
without a solvent,1
in carbon disulfide
in acetic acid
and in other organic solvents.5
The quantitative aspects of the bromination in various solvents have been investigated by Kröhnke.3
The use of ether
in the method described is based on the use of this solvent in the bromination of desoxybenzoin
is a useful reagent for the identification of organic acids by conversion to crystalline phenacyl esters.4
This preparation is referenced from:
Chemical Abstracts Nomenclature (Collective Index Number);
calcium chloride (10043-52-4)
acetic acid (64-19-7)
hydrogen bromide (10035-10-6)
carbon tetrachloride (56-23-5)
aluminum chloride (3495-54-3)
carbon disulfide (75-15-0)
Acetophenone, α-bromo- (70-11-1)
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