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Org. Synth. 1925, 5, 21
DOI: 10.15227/orgsyn.005.0021
p-BROMOTOLUENE
[Toluene, p-bromo-]
Submitted by L. A. Bigelow
Checked by C. S. Marvel and A. E. Broderick.
1. Procedure
A mixture of 63 g. (0.25 mole) of crystallized copper sulfate, 20 g. (0.31 atom) of copper turnings, 154 g. (1.1 moles) of sodium bromide dihydrate, 30 g. (16.3 cc., 0.28 mole) of concentrated sulfuric acid (sp. gr. 1.84), and 1 l. of water is refluxed over a flame for three to four hours until the color becomes yellowish (Note 1).
When the hydrobromic acid-cuprous bromide solution is ready for use, the diazonium solution is prepared. A solution of 107 g. (1 mole) of p-toluidine and 196 g. (107 cc., 1.9 moles) of concentrated sulfuric acid (sp. gr. 1.84) in 1 l. of water is cooled below 20° and diazotized with a solution of 70 g. (1 mole) of sodium nitrite in 125 cc. of water. This requires about twenty to thirty minutes when the temperature is maintained between 15° and 20° by means of an ice bath.
A 5-l. round-bottomed flask containing the hydrobromic acid-cuprous bromide solution, is arranged for steam distillation. After the copper solution is heated to boiling, the diazonium solution is gradually added from a separatory funnel and a vigorous current of steam is passed through the reaction mixture at the same time. This procedure requires about two hours.
The aqueous distillate is made alkaline with sodium hydroxide solution and the p-bromotoluene is separated from the water layer (Note 2). The crude product weighs 131–137 g. For purification the crude product is washed once with concentrated sulfuric acid (Note 3) and then with water. It is dried over a little calcium chloride, filtered, and distilled. The yield of pure product amounts to 120–126 g. (70–73 per cent of the theoretical amount) boiling at 183–185° and melting at 25–26°.
2. Notes
1. If the color of the solution has not been discharged after heating for three to four hours, a few grams of sodium sulfite may be added to complete the reduction.
2. A small amount of ether or benzene may be used to aid in the separation if it is needed.
3. The sulfuric acid treatment is necessary if a colorless product is to be obtained. If ether is used in the extraction of the p-bromotoluene, it must be removed before washing with sulfuric acid.
3. Discussion
p-Bromotoluene can be prepared by the bromination of toluene with bromine1 or hypobromous acid;2 and, preferably, by the diazotization of p-toluidine followed by replacement of the diazonium group by bromine.3
This preparation is referenced from:

References and Notes
  1. Glinzer and Fittig, Ann. 136, 301 (1865); Hübner and Wallach, Ann. 154, 294 (1870); Z. Chem. 138 (1869); Michaelis and Genzken, Ann. 242, 165 (1887); Schramm, Ber. 18, 608 (1885); Gay, Ducelliez and Raynaud, Compt. rend. 158, 1806 (1914); Varma and Narayan, Quart. J. Indian Chem. Soc. 4, 283 (1927) [Chem. Zentr. I, 489 (1928)].
  2. Stark, Ber. 43, 673 (1910).
  3. Acree, Ber. 37, 994 (1904); Neogi and Mitra, J. Chem. Soc. 1332 (1928).

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

calcium chloride (10043-52-4)

sulfuric acid (7664-93-9)

Benzene (71-43-2)

ether (60-29-7)

sodium sulfite (7757-83-7)

sodium hydroxide (1310-73-2)

bromine (7726-95-6)

copper sulfate (7758-98-7)

sodium nitrite (7632-00-0)

copper turnings (7440-50-8)

toluene (108-88-3)

hypobromous acid (13517-11-8)

sodium bromide dihydrate

hydrobromic acid-cuprous bromide

p-toluidine (106-49-0)

p-Bromotoluene,
Toluene, p-bromo- (106-38-7)