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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:

References and Notes
  1. Org. Syntheses Coll. Vol. 1, 77 (1941).
  2. Claisen and Claparede, Ber., 14, 2463 (1881).
  3. Watson, J. Chem. Soc., 85, 464 (1904).
  4. Cromwell, J. Am. Chem. Soc., 62, 3471 (1940).
  5. Southwick, Pursglove, and Numerof, J. Am. Chem. Soc., 72, 1600 (1950).

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)