Organic Syntheses, CV 1, 136
Submitted by L. A. Bigelow
Checked by C. S. Marvel and A. E. Broderick.
1. Procedure
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. Discussion
This preparation is referenced from:
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