Submitted by Johannes S. Buck and Walter S. Ide.
Checked by John R. Johnson and Paul W. Vittum.
1. Procedure
A solution of
450 g. (2 moles) of stannous chloride crystals (Note
1) in
600 cc. of concentrated hydrochloric acid is placed in a
3-l. beaker provided with an
efficient mechanical stirrer and cooled in an
ice bath. When the temperature of the solution has fallen to +5°,
100 g. (0.66 mole) of m-nitrobenzaldehyde (Note
2) is added in one portion. The temperature rises slowly at first, reaching 25–30° in about five minutes, then rises very rapidly to about 100°. Stirring must be vigorous or the reaction mixture may be forced out of the beaker (Note
3). During the reaction the
nitrobenzaldehyde dissolves, and an almost clear, red solution is obtained. The solution is cooled in an ice-salt mixture until the temperature has fallen to about +2°. During the cooling, orange-red crystals separate and a pasty suspension results.
A
250-cc. separatory funnel is fixed so that its stem extends below the surface of the pasty suspension. A solution of
46 g. (0.67 mole) of sodium nitrite in 150 cc. of water is placed in the funnel and is slowly added to the well-stirred mixture until it shows a positive starch-iodide test for
nitrous acid. The temperature of the mixture is maintained between 0° and +5° (Note
4) throughout the addition of the nitrite solution, which requires about ninety minutes. Usually, all but
5–8 cc. of the nitrite solution must be added before a positive test for
nitrous acid appears.
During the latter part of the diazotization of the
aminobenzaldehyde, a hot solution of
cuprous chloride is prepared. In a
5-l. round-bottomed flask,
189 g. (0.75 mole) of powdered copper sulfate crystals and
161 g. of sodium chloride are dissolved in 600 cc. of hot water, and to this solution is added a solution of
41 g. (0.22 mole) of sodium metabisulfite (Na2S2O5) and
27 g. (0.67 mole) of sodium hydroxide in 300 cc. of water. The final temperature of the resulting
cuprous chloride solution should be about 75°.
The diazonium solution is added to the hot
cuprous chloride solution while the latter is shaken by hand but is not cooled. After the solutions are thoroughly mixed,
840 cc. of concentrated hydrochloric acid is added and the mixture is allowed to stand overnight. The reaction mixture is steam-distilled to separate the
m-chlorobenzaldehyde, which is collected practically completely in the first 1.5 l. of distillate. The
m-chlorobenzaldehyde is removed from the aqueous distillate by extraction with two
150-cc. portions of ether, and the ethereal solution is dried with
10–15 g. of anhydrous calcium chloride. After being decanted from the drying agent, the
ether is distilled, and the residual liquid is distilled under diminished pressure. The
m-chlorobenzaldehyde boils at
84–86°/8 mm.,
107–109°/26 mm. (Note
5). The yield is
70–74 g. (
75–79 per cent of the theoretical amount) (Note
6).
2. Notes
3. During the vigorous reaction it is advisable to keep the cooling bath and the reaction mixture well stirred. Less satisfactory yields were obtained when the reaction was moderated by adding the
nitrobenzaldehyde in several portions.
4. At temperatures below 0° the speed of diazotization is markedly decreased. Above +5° some decomposition of the diazonium salt takes place.
5. Since
m-chlorobenzaldehyde is oxidized easily by atmospheric
oxygen, it should be stored in a
tightly corked or sealed container.
A solution of
stannous bromide is prepared by heating
119 g. (1 gram atom) of mossy tin with
705 g. (4 moles) of 46 per cent hydrobromic acid for two hours on a
steam bath, with mechanical stirring. The solution is cooled to 40°, and
50 g. (0.33 mole) of m-nitrobenzaldehyde is added in one portion, with continued stirring. The temperature rises from the heat of reaction and finally reaches about 105°. After heating for one-half hour longer on a steam bath, the reaction mixture is cooled to 0° and the
aminobenzaldehyde diazotized by the gradual addition of
23 g. (0.33 mole) of sodium nitrite in 75 cc. of water. The diazonium solution is poured into a hot suspension of
cuprous bromide,
100 cc. of 46 per cent hydrobromic acid is added, with stirring, and the mixture is allowed to stand overnight. The mixture is steam-distilled and the
m-bromobenzaldehyde isolated by
ether extraction and vacuum distillation; b.p.
90–92°/4 mm. The yield is
41 g. (
67 per cent of the theoretical amount). (F. T. Tyson, private communication.)
3. Discussion
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