Org. Synth. 1933, 13, 20
DOI: 10.15227/orgsyn.013.0020
ISOBUTYL BROMIDE
[Propane, 1-bromo-2-methyl-]
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.
In the preparation of these three bromides and
isobutyl bromide as well, the
phosphorus tribromide procedure described above gives purer products in better yields than the hydrobromic-sulfuric acid method described in
Org. Syn. Coll. Vol. I, 1941, 25. The
phosphorus tribromide method is not convenient for the preparation of
tertiary butyl bromide; the product is difficult to purify.
3. Discussion
Isobutyl bromide has been prepared from
isobutyl alcohol by the action of
bromine and
phosphorus,
1 aqueous
hydrobromic acid,
2 and gaseous
hydrobromic acid;
3 from
isobutylene and gaseous
hydrogen bromide;
4 or
hydrogen bromide in glacial
acetic acid;
5 and by the rearrangement of
tertiary butyl bromide at 210–220°.
6 A number of bromides, including
isobutyl bromide, have been prepared by the action of
phosphorus tribromide on alcohols.
7 The procedure described above is a modification of one used for preparing
cyclopentyl bromide.
8
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
red phosphorus
potassium carbonate (584-08-7)
sulfuric acid (7664-93-9)
acetic acid (64-19-7)
HYDROBROMIC ACID,
hydrogen bromide (10035-10-6)
bromine (7726-95-6)
PHOSPHORUS (7723-14-0)
Isopropyl bromide (75-26-3)
n-PROPYL BROMIDE (106-94-5)
sec.-BUTYL BROMIDE (78-76-2)
tertiary butyl bromide,
t-butyl bromide (507-19-7)
phosphorus tribromide (7789-60-8)
carbon tetrachloride (56-23-5)
isobutyl alcohol (78-83-1)
Isobutyl bromide,
Propane, 1-bromo-2-methyl- (78-77-3)
isobutylene (9003-27-4)
cyclopentyl bromide (137-43-9)
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