Hydrogen Bromide → 3-(2,2-Dibromovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid

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Reaction Steps

Anhydrous hydrogen bromide gas was introduced through a pipet (below the liquid level in the flask) to a stirred suspension of a small portion of aluminum shot in methylene bromide (250 ml) at 60°. The temperature was maintained at 60°-65° by heating or cooling as required during the portionwise addition of the aluminum shot (9.67 g, 0.358 mole total). The flow of HBr was maintained until all the aluminum had reacted to produce a cloudy brown mixture. The temperature of the reaction mixture was then reduced to 0°-5°, and a solution of cis-3-(2,2-dichlorovinyl)2,2-dimethylcyclopropanecarboxylic acid (50.0 g, 0.24 mole) in methylene bromide was added dropwise over a period of an hour to the vigorously stirred mixture under a nitrogen atmosphere. The reaction mixture was allowed to stir for 1 hour 20 minutes at 0.5°; then a flow of nitrogen was passed through the reaction mixture at reduced pressure (20 mm) for 11/2 hours. The entire reaction mixture was then poured slowly into a mixture of ice and 1 N hydrochloric acid and extracted twice with diethyl ether. The combined ethereal solution was dried over anhydrous magnesium sulfate, and the ether was removed under reduced pressure, affording a gray-brown solid, which was dried in a vacuum oven, affording 3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylic acid (70.7 g). The crude product was recrystallized from hexane and sublimed. The cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylic acid thus obtained was 93% pure by glc analysis.

Provenance & Evidence