Org. Synth. 1933, 13, 20
DOI: 10.15227/orgsyn.013.0020
[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

References and Notes
  1. Wurtz, Ann. 93, 114 (1855).
  2. Norris, Am. Chem. J. 38, 640 (1907).
  3. Fournier, Bull. soc. chim. (3) 35, 623 (1906); Longinov and Lerman, Khim Farm. Prom. 1933, 14 [C. A. 27, 3443 (1933)].
  4. Brunel, J. Am. Chem. Soc. 39, 1978 (1917).
  5. Ipatiew and Ogonowsky, Ber. 36, 1988 (1903).
  6. Faworsky, Ann. 354, 343 (1907).
  7. Reynolds and Adkins, J. Am. Chem. Soc. 51, 280 (1929); Tseng and Hou, J Chinese Chem. Soc. 2, 57 (1934) [C. A. 28, 3711 (1934)].
  8. Adams and Noller, J. Am. Chem. Soc. 48, 1084 (1926).

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)

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)