Submitted by R. B. Woodward
Checked by C. S. Hamilton and Raymond J. Andres.
1. Procedure
A solution of
450 g. (2 moles) of powdered stannous chloride dihydrate (Note
1) in
600 ml. of concentrated hydrochloric acid in a
3-l. beaker provided with an efficient mechanical stirrer is cooled in an
ice-salt bath. When the temperature of the solution has fallen to 5°, the ice bath is removed, and
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 5 minutes. As it then rises rapidly to about 100° the ice-salt bath is again placed around the beaker. Stirring must be vigorous or the reaction mixture may be forced out of the beaker (Note
3). During the reaction the
m-nitrobenzaldehyde dissolves, and an almost clear red solution is obtained. The solution is cooled with very slow stirring (Note
4) in an ice-salt mixture for 2.5 hours. The orange-red paste of the stannichloride of
m-aminobenzaldehyde (Note
5) is filtered on a
sintered-glass funnel (Note
6).
A suspension of the material in
600 ml. of concentrated hydrochloric acid is stirred mechanically in a
3-l. beaker which is set in an ice-salt bath. A solution of
46 g. of sodium nitrite in 150 ml. of water in a
250-ml. dropping funnel fixed with its stem below the surface of the suspension is added slowly while the temperature of the mixture is kept at 4–5° (Note
7). After the addition is completed (in approximately 80 minutes), stirring in the ice-salt bath is continued for 1 hour to crystallize completely the stannichloride of the diazonium salt. The reddish brown salt is filtered on a sintered glass funnel (Note
6).
The damp salt is added cautiously in small portions to 1.7 l. of boiling water in a
4-l. beaker in the course of 40 minutes. During the reaction, the water lost by vaporization is replaced (Note
8). The solution is treated with
4 g. of Norit, boiled a few minutes, and filtered hot. The red filtrate is kept in an
icebox for 12–16 hours; during this time scratching is employed occasionally to induce crystallization (Note
9). The yield of orange crystals melting at
99–101° is
48–52 g. (
59–64%). A solution of this product in about
1 l. of boiling benzene is treated with
Norit, filtered, and concentrated to 300 ml. On cooling,
41–45 g. (
51–56%) of light-tan crystals melting at
101–102° is obtained (Note
10).
2. Notes
3. Less satisfactory yields are obtained when the reaction is moderated by the addition of the
m-nitrobenzaldehyde in several portions.
4. Stirring must be very slow since gradual cooling is necessary in order to obtain particles large enough to permit fairly rapid filtration.
6. As a substitute for the
sintered-glass funnel, a
large Büchner funnel provided with an asbestos fiber mat under the filter paper will serve. The asbestos mat can be washed and used repeatedly.
7. Best results are obtained by keeping the temperature during diazotization at 4–5°. Below 0° the speed of diazotization is greatly decreased, and above 5° the diazonium salt begins to decompose.
8. Concentrating the solution below 1.7 l. results in markedly decreased purity.
9. If scratching does not succeed in inducing crystallization, a small portion of the solution may be removed and evaporated for seed.
10. According to the submitter, further purification can be effected by sublimation: the material is placed in the bottom of a
Pyrex desiccator which is then evacuated and placed on a
steam bath overnight. The mat of interwoven needles can be removed easily. One crystallization from
benzene gives
37–40 g. (
47–49%) of needles melting at
103–104°.
3. Discussion
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