Bromination of Ketones and Dehydrobromination

Stirring. The succinimide is removed by suction filtration and washed twice with 10-mI portions of carbon tetrachloride. The combined filtrate and washings are fractionally distilled at atmospheric pressure to remove the carbon tetrachloride and excess olefin (steam bath). The residue is distilled under vacuum, giving about 60 % yield of 3-bromo-cyclohexene, bp 68715 mm or 4472 mm. 

The above procedure is applied to 2-heptene (9.8 g, 0.1 mole), 11.5 g (0.066 mole) of NBS, and 0.1 g of benzoyl peroxide in 50 ml of carbon tetrachloride. The mixture is refluxed with stirring for 2 hours. Final fractionation yields 50-65% of 4-bromo-2-heptene, bp 70-71732 mm. 

A mixture of ethylbenzene (11.7 g, 0.11 mole), NBS (17.8 g, 0.10 mole), benzoyl peroxide (0.24 g), and carbon tetrachloride (55 ml) is refluxed as in the above experiments for 25 minutes. After removal of the succinimide and solvent, the residue is distilled, giving the product in about 80% yield, bp 87-90°/14 mm. 

Base catalyzed dehydrobromination of a-bromoketones is frequently employed in steroidal systems as a means to obtain a,/9-unsaturated ketones (12). An example of this reaction employing lithium carbonate as the base is also given. 

The bromination given in the preceding experiment may be applied to trans-lO-methyl-2-decalone prepared in Chapter 3, Section III. The product is recrystallized from petroleum ether-benzene (10 1) giving colorless needles, mp 101-103°. 

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