A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1943, 23, 67
DOI: 10.15227/orgsyn.023.0067
[Pentane, 1,5-dibromo-]
Submitted by D. W. Andrus
Checked by Nathan L. Drake and Charles M. Eaker.
1. Procedure
A hydrobromic acid solution [Org. Syntheses Coll. Vol. 1, 26 (1941)] is prepared in a 500-ml. round-bottomed flask by passing sulfur dioxide into a mixture of 120 g. (37.7 ml., 0.75 mole) of bromine, 50 ml. of water, and 150 g. of crushed ice. This is equivalent to a mixture of 253 g. (1.5 moles) of 48% hydrobromic acid and 74 g. of concentrated sulfuric acid. To the mixture 21.5 g. (0.25 mole) of tetrahydropyran (p. 794) is added, a reflux condenser is attached to the flask, and the light-brown homogeneous mixture is refluxed for 3 hours (Note 1).
The heavy lower layer is separated (Note 2), washed once with a saturated solution of sodium bicarbonate and once with water, and then dried over 4–5 g. of anhydrous calcium chloride. The crude product is decanted from the calcium chloride, and the drying agent is rinsed once or twice with a small quantity of ethyl bromide which is added to the main product. The mixture is distilled under reduced pressure, and the pentamethylene bromide, which weighs 46–47 g. (80–82%), is collected at 104–106°/19 mm.
2. Notes
1. The submitter refluxed the mixture for 10 hours, but the checkers obtained equally good yields in 3 hours.
2. The upper aqueous layer contains considerable unchanged hydrobromic acid. If this layer is distilled, about 150 g. (0.9 mole) of constant-boiling hydrobromic acid (b.p. 123–124°/748 mm.) may be recovered.
3. Discussion
The methods of preparing pentamethylene bromide are given in Org. Syntheses Coll. Vol. 1, 428 (1941), where the preparation of the dihalide from benzoylpiperidine and phosphorus pentabromide is described in detail. The procedure given above is based upon the work of Paul.1

References and Notes
  1. Paul, Bull. soc. chim. France, (4) 53, 1489 (1933).

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

calcium chloride (10043-52-4)

sulfuric acid (7664-93-9)

sodium bicarbonate (144-55-8)


bromine (7726-95-6)

sulfur dioxide (7446-09-5)

Ethyl bromide (74-96-4)

Benzoylpiperidine (776-75-0)

pentamethylene bromide,
Pentane, 1,5-dibromo- (111-24-0)

Tetrahydropyran (142-68-7)

phosphorus pentabromide (7789-69-7)