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Org. Synth. 1925, 4, 9
DOI: 10.15227/orgsyn.004.0009
α-BROMO-n-CAPROIC ACID
[Caproic acid, α-bromo-]
Submitted by H. T. Clarke and E. R. Taylor.
Checked by C. S. Marvel and R. L. Shriner.
1. Procedure
Two hundred grams (1.72 moles) of freshly distilled dry n-caproic acid (Note 1) is placed in a 1-l. flask with 300 g. (96 cc., 1.88 moles) of bromine which has been dried by washing once with 200 cc. of concentrated sulfuric acid (Note 2). A 3-cc. portion of phosphorus trichloride is cautiously added and the flask connected to a reflux condenser (Note 3), the top of which is connected with a trap and absorption bottle containing water. The mixture is then heated in a water or oil bath to 65–70°, at which temperature the reaction commences and hydrogen bromide is given off smoothly. After five to six hours, the bromine has all reacted (Note 4). Towards the end of the reaction, the temperature is allowed to rise to about 100°. The contents of the flask are now distilled under diminished pressure (Note 5). The fraction boiling at 132–140°/15 mm. is collected and weighs 280–298 g. (83–89 per cent of the theoretical amount).
2. Notes
1. The n-caproic acid can be prepared by the general procedure described in Org. Syn. 11, 78, Note 8.
2. The reagents must be dry or the yield will be lowered.
3. A flask fitted with a ground-glass connection to the reflux condenser will assist in reducing the amount of tar.
4. For larger runs, a longer time is required. A run of 2 kg. of caproic acid requires about fifteen hours.
5. It is best to distil the first low-boiling fractions with a water pump, since a considerable amount of hydrogen bromide is evolved. In order to obtain a light-colored product, the distillation should take place under as low pressure as possible. The α-bromo-n-caproic acid boils at 116–125°/8 mm. The product obtained is sufficiently pure for most purposes; upon redistillation, however, it comes over almost entirely between 128° and 131°/10 mm.
3. Discussion
α-Bromo-n-caproic acid can be prepared by heating n-caproic acid with bromine in a sealed tube to 140°1 and with bromine and phosphorus;2 and by the action of heat on α-bromo-α-butylmalonic acid.3
This preparation is referenced from:

References and Notes
  1. Hüfner, Z. Chem. 616 (1868); J. prakt. Chem. (2) 1, 7 (1870).
  2. Auwers and Benhardi, Ber. 24, 2222 (1891); Fischer, Ber. 33, 2381 (1900); Abderhalden, Froehlich and Fuchs, Z. physiol. Chem. 86, 455 (1913).
  3. Adams and Marvel, J. Am. Chem. Soc. 42, 319 (1920); Marvel and du Vigneaud, Org. Syn. 11, 22.

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

sulfuric acid (7664-93-9)

hydrogen bromide (10035-10-6)

bromine (7726-95-6)

PHOSPHORUS (7723-14-0)

Caproic acid, α-bromo-,
α-bromo-n-caproic acid (616-05-7)

phosphorus trichloride (7719-12-2)

Caproic acid,
n-caproic acid (142-62-1)

α-bromo-α-butylmalonic acid