A 2-l. three-necked flask, supported in an oil bath, is fitted with a mechanical stirrer and an inlet tube which reaches almost to the bottom of the flask. In it is placed 696 g. (4 moles) of decamethylene glycol, and, after the oil bath is heated to 95–100°, a rapid stream of dry hydrogen bromide is introduced, with stirring. When the mixture becomes saturated with the gas, as shown by vigorous fuming at the open neck of the flask (Note 1), the temperature of the oil bath is raised to 135° and a slow current of hydrogen bromide is passed in for 6 hours (Note 2).

After cooling, the crude product is transferred to a separatory funnel and the lower aqueous layer is drawn off and discarded. The upper layer is washed once with an equal volume of warm water, and then with successive portions of 10% sodium carbonate solution until all acid has been removed. It is then washed once with warm water, which is separated as completely as possible (Note 3). The product thus washed is distilled from a Claisen flask under reduced pressure. The first few drops of distillate containing some water are discarded: the main fraction distils at 139–142°/2 mm. The yield is 1080 g. (90%) (Note 4).