Org. Synth. 1929, 9, 22
DOI: 10.15227/orgsyn.009.0022
o-BROMOTOLUENE
[Toluene, o-bromo-]
Submitted by L. A. Bigelow
Checked by C. S. Marvel and S. V. Puntambeker.
1. Procedure
A solution of 162 g. (1.5 moles) of commercial o-toluidine in 880 cc. (6 moles) of 40 per cent commercial hydrobromic acid (Note 1) in a 3-l. flask is cooled to 10° and diazotized with 116 g. (1.7 moles) of coarsely powdered commercial sodium nitrite, added about 10 g. at a time. After each addition the flask is stoppered and shaken until all the red fumes are absorbed. The temperature must be kept below 10°. When diazotization is complete, 5 g. of copper powder (Note 2) is added, the flask is attached to a reflux condenser and heated very cautiously. As soon as the first sign of reaction is observed, the flask is cooled with ice. Nitrogen is evolved vigorously. When the reaction subsides, the mixture is heated one-half hour on the steam bath.
Then 1 l. of water is added and the mixture is distilled with steam until about 1.5 l. has passed over. The distillate is made alkaline with about
10 g. of powdered sodium hydroxide and the lower red layer of crude
o-bromotoluene separated
(Note 3). This weighs about
140 g. It is washed with concentrated
sulfuric acid, which removes almost all the color, and then twice with water. It is dried over a little
calcium chloride, filtered and distilled twice from a
modified Claisen flask (p. 130). The yield of pure product boiling at
178–181° is
110–120 g. (
43–47 per cent of the theoretical amount).
2. Notes
1.
If
48 per cent (constant boiling) hydrobromic acid is used the diazotization is very difficult to control. The reaction becomes very vigorous and forces out the stopper.
2.
Either reduced
copper or fine
copper filings may be used.
3.
This gives as good results as when the
o-bromotoluene is extracted from the alkaline mixture with
ether.
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3. Discussion
o-Bromotoluene can be prepared by the bromination of
toluene;
1 by the bromination of
potassium p-toluenesulfonate and subsequent hydrolysis;
2 and by the diazotization of
o-toluidine under different conditions.
3
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
calcium chloride (10043-52-4)
sulfuric acid (7664-93-9)
ether (60-29-7)
sodium hydroxide (1310-73-2)
HYDROBROMIC ACID (10035-10-6)
nitrogen (7727-37-9)
sodium nitrite (7632-00-0)
copper,
copper powder,
copper filings (7440-50-8)
toluene (108-88-3)
o-Bromotoluene,
Toluene, o-bromo- (95-46-5)
o-toluidine (95-53-4)
potassium p-toluenesulfonate
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