Organic Syntheses, CV 2, 358
Submitted by C. R. Noller and R. Dinsmore.
Checked by Frank C. Whitmore, D. E. Badertscher, and A. R. Lux.
1. Procedure
In a
2-l. three-necked flask, fitted with a
mechanical stirrer, a
thermometer, and a
dropping funnel, is placed
518 g. (643 cc., 7 moles) of dry isobutyl alcohol (b.p.
106–108°). The alcohol is cooled to −10° by immersing the flask in an
ice-salt bath, and
695 g. (244 cc., 2.56 moles) of phosphorus tribromide (Note
1) is slowly added with stirring at such a rate as to keep the temperature below 0° (about four hours). The cooling bath is removed, and stirring is continued until the mixture reaches room temperature; it is then allowed to stand overnight. The stirrer, funnel, and thermometer are removed, and the flask is fitted with a
30-cm. fractionating column and a
condenser. The crude
isobutyl bromide is distilled from the reaction mixture under diminished pressure, e.g., at about 50°/200 mm. (Note
2).
The distillate is cooled to about 0° and washed three times with
50-cc. portions of concentrated sulfuric acid cooled to 0°; it is then shaken with
25 g. of anhydrous potassium carbonate until the odor of
hydrobromic acid disappears. It is distilled through a
1-m. fractionating column at atmospheric pressure collecting the portion boiling at
91–93° (
88.5–90.5°/728 mm.), or under reduced pressure through a 70 by
2-cm. total reflux, adjustable take-off, adiabatic column (Note
3), b.p.
41–43°/135 mm. The product weighs
525–570 g. (
55–60 per cent of the theoretical amount) (Note
4).
2. Notes
1. The
phosphorus tribromide boiled at
171–173° (
168–170°/725 mm.), and was prepared in
90–95 per cent yield by adding
bromine to a stirred suspension of
red phosphorus in
carbon tetrachloride. A
good fractionating column is necessary. Old,
red phosphorus containing acids of
phosphorus gives a poorer yield.
2. In some runs, the crude bromide was successfully distilled at atmospheric pressures; in others it decomposed violently. With reduced pressure no difficulty was experienced. A
water pump with an adjustable leak in the vacuum line was used.
3. The column used with reduced pressure was similar to those described by Whitmore and Lux, J. Am. Chem. Soc.
54, 3451 (1932). The product, fractionated under reduced pressure using a reflux ratio of 5:1, contained less than 1 per cent of
tertiary butyl bromide.
4. By similar procedures, the following bromides can be prepared with the yields indicated:
sec.-butyl, b.p.
90–93°,
80 per cent;
n-propyl, b.p.
70–73°,
95 per cent;
isopropyl, b.p.
60–63°,
68 per cent.
3. Discussion
This preparation is referenced from:
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