Org. Synth. 1947, 27, 5
DOI: 10.15227/orgsyn.027.0005
BENZALACETONE DIBROMIDE
[2-Butanone, 3,4-dibromo-4-phenyl-]
Submitted by Norman H. Cromwell and Richard Benson.
Checked by R. L. Shriner and William O. Foye.
1. Procedure
In a
1-l. three-necked round-bottomed flask fitted with an efficient mechanical stirrer, a thermometer, and a 125-ml. dropping funnel are placed
100 g. (0.68 mole) of pure, redistilled benzalacetone1 and
300 ml. of carbon tetrachloride. The reaction flask is immersed in an
ice-water bath to maintain the reaction mixture between 10° and 20°. With stirring, a cooled solution of
109.5 g. (34.2 ml., 0.68 mole) of bromine in
60 ml. of carbon tetrachloride is run through the
dropping funnel as rapidly as the color is destroyed
(Note 1). During this addition the reaction flask should be shielded from direct sunlight
(Note 2).
After all the bromine has been added, stirring is continued for 4–5 minutes longer and the dibromide is collected by filtration on an 11-cm. Büchner funnel, using suction. The product is washed with 100 ml. of warm 75% ethanol (Note 3). The crude product is purified by dissolving in the minimum amount of boiling methanol (800–1000 ml.) and cooling the solution in an ice bath for 4 hours. The product is collected by filtration and dried in a vacuum desiccator in the absence of light for 24 hours. The yield amounts to 110–120 g. (52–57%) of white needles which melt at 124–125° (Note 4).
2. Notes
1.
Until a considerable amount of the dibromide has precipitated, the
bromine solution may be run into the reaction mixture as fast as the color is discharged, within the temperature limits of 10–20°. As the mixture becomes thick with the precipitated bromide it is necessary to reduce the speed of the addition of the
bromine solution considerably.
2.
Strong sunlight seems to favor the substitution of the available
α-hydrogen as evidenced by the strong evolution of
hydrogen bromide.
3.
If the crude product is dried it is found to melt at
114–117° and to weigh
138–144 g. This is probably a mixture of the two racemic forms.
4.
Evaporation and subsequent cooling of the filtrate give a second crop of white crystals, about
15 g., melting at
112–115°. This may be the lower-melting racemate.
3. Discussion
Benzalacetone dibromide has been prepared by the addition of
bromine to a solution of
benzalacetone in
chloroform,
2 in
carbon disulfide,
3 and in
carbon tetrachloride;
4 and by the reaction of
benzalacetone with
N-bromosuccinimide.
5
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
α-hydrogen
ethanol (64-17-5)
methanol (67-56-1)
chloroform (67-66-3)
hydrogen bromide (10035-10-6)
bromine (7726-95-6)
carbon tetrachloride (56-23-5)
Benzalacetone (122-57-6)
carbon disulfide (75-15-0)
Benzalacetone dibromide,
2-Butanone, 3,4-dibromo-4-phenyl- (6310-44-7)
N-bromosuccinimide (128-08-5)
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