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).