For anaesthetic purposes, ethyl bromide may be prepared by distilling a mixture

1 Trans. Chem. Soc, 25, 1874, 641. 2 D.R.-P. 280740, 1913 of sulphuric acid (1 part), strong alcohol (1 part, by weight) and sodium bromide (2 parts). The acid is first carefully run into the alcohol, the mixture being kept cooled. According to F. E. Weston,1 the alcohol should be mixed with 5 to 10 per cent. of its weight of water. This is conveniently added in the form of ice after the mixture of acid and alcohol has cooled down. To the cold mixture the sodium bromide, coarsely powdered, is added, and the whole very gently distilled, first on a water-bath and finally on a sand-bath, the temperature being only allowed to rise as the distillation slackens. Ethyl bromide distils over. It is purified by washing with dilute sodium carbonate solution, and dried with fused calcium chloride, followed by re-distillation if necessary. To remove any ether which it may contain, the bromide can be shaken up repeatedly with a small quantity of strong sulphuric acid.2

A less pure product is obtained by the action of bromine and red phosphorus upon alcohol. One part of the phosphorus is mixed with 6 parts of strong alcohol and 6 parts of bromine are allowed to run slowly into the mixture, which is kept cooled and shaken during the addition. After standing for a few hours the mixture is distilled from a water-bath, the temperature of which is raised slowly. The distillate is shaken with dilute soda solution to remove alcohol and free bromine, and the ethyl bromide drawn off, further purified by washing with water, dried over calcium chloride, and re-distilled.

The chemical reaction involved may be expressed thus: -

5C2H5.OH

+

5Br

+

P

=

5C2H5Br

+

H3PO4

+

H1O.

Alcohol.

Ethyl bromide.

For medical purposes ethyl bromide prepared by the first method is preferred, as it is more free from impurities than that made by the phosphorus process.

Ethyl bromide is a colourless liquid, of boiling point 38. 8°. It is used as an inhalation anaesthetic in minor medical operations, either alone or mixed with ethyl chloride or methyl chloride. It is also employed as an alkylating agent, though less frequeutly than ethyl chloride.