β-ETHOXYETHYL BROMIDE

In a 2-l. three-necked flask, fitted with a mechanical stirrer (Note 1), a reflux condenser, and a dropping funnel, is placed 630 g. (670 ml., 7 moles) of β-ethoxyethyl alcohol (Note 2). The stirrer is started, and 600 g. (210 ml., 2.2 moles) (Note 3) of phosphorus tribromide is added from the dropping funnel over a period of 1.5–2 hours. The temperature is permitted to rise until the reaction mixture refluxes gently.

The mixture is then distilled, and the distillate boiling below 150° is collected in a 2-l. flask containing 1 l. of water. The lower layer of crude β-ethoxyethyl bromide is separated and dried over 10 g. of calcium chloride. The liquid is decanted and distilled through a 25-cm. fractionating column, and the fraction boiling at 125–127°/760 mm. is collected (Note 4). The yield of pure product is 660–670 g. (65–66% based on the phosphorus tribromide).

1. A rubber sleeve lubricated with a drop of oil provides an effective seal for the stirrer.

2. Technical β-ethoxyethyl alcohol is marketed commercially as Cellosolve; it should be dried over calcium oxide and distilled.

3. A slight excess of β-ethoxyethyl alcohol gives the best results.

4. The first fraction, boiling at 38–40°, is ethyl bromide, and it weighs 120–130 g. Lower yields (56–59%) of β-ethoxyethyl bromide are obtained by distillation without a fractionating column. The residue, however, should not be overheated, for at high temperatures phosphorous acid decomposes to give phosphine and perhaps even elementary phosphorus, and then, when air is admitted to the apparatus an explosion may occur. A minor explosion in connection with this preparation has been reported (N. L. Drake, private communication) and a similar situation has been observed in reactions with phosphorus trichloride.¹