Submitted by F. D. Hager
Checked by Henry Gilman and R. McCracken.
1. Procedure
In a
2-l. three-necked, round-bottomed flask, fitted with a very
efficient mechanical stirrer, a
100-cc. separatory funnel, and a
large air-cooled reflux condenser (Note
1), the upper part of which is bent downwards and attached to a
vertical water condenser, are placed
176 g. (1.04 moles) of ground diphenylamine (Note
2),
204 g. (1 mole) of iodobenzene,
1 l. of nitrobenzene (Note
3),
138 g. (1 mole) of finely powdered anhydrous potassium carbonate, and
5 g. of copper powder (Note
4).
The reaction mixture is then stirred very vigorously and boiled at such a rate that the
nitrobenzene condenses in the upper third of the air-cooled reflux condenser and flows back in an almost steady stream. The water formed in the reaction passes over, together with a small amount of
nitrobenzene and
iodobenzene, and is condensed by the water-cooled condenser. This distillate is freed of water by shaking with a small quantity of
sodium sulfate and returned at intervals through the
separatory funnel to the reaction flask. Heating is continued for about twenty-four hours or until the reaction is complete, as is evidenced by the non-evolution of water (Note
5).
The reaction mixture is allowed to cool somewhat and is then transferred to a
5-l. flask, and the
nitrobenzene together with a little of the excess
diphenylamine is removed by steam distillation. During distillation the flask should be heated to prevent excessive condensation of steam (Note
6). Steam distillation should be continued until a liter of distillate contains less than 5 cc. of water-insoluble material (Note
7).
The reaction mixture is cooled, and the crude amines which separate are collected on a
suction funnel and washed twice with 400-cc. portions of water. The filtrate and washings should be saved for the recovery of
iodine (Note
8). The precipitate on the funnel is transferred to a
2-l. beaker, dissolved in about
1 l. of benzene, filtered, and the benzene-insoluble part washed three times with
75-cc. portions of benzene. The
benzene solution and washings are combined and separated mechanically from as much water as possible. The water is then completely removed by distilling until the distillate comes over clear. If necessary, dry
benzene is added to the solution in order to have a final volume of about 1200 cc.
After standing about three hours, the
diphenylamine hydrochloride is filtered and washed with
benzene (Note
10). The
benzene is distilled from the filtrate (Note
11), and the residual
triphenylamine is transferred to a
500-cc. modified Claisen flask (p. 130) and distilled under reduced pressure. The first fraction consists of some
benzene, then the temperature rises rapidly and a few cubic centimeters of deeply colored distillate come over just before the amine fraction, which is collected at 195–205°/10–12 mm. The distillate is a yellow liquid which soon solidifies to a light yellow solid. The side arm of the
distilling flask should be of rather large bore (about 10 mm.) to prevent clogging by the amine which solidifies. The crude product weighs
220–235 g. and melts at
120–124°.
In order to obtain a pure product the amine is dissolved in about
700 cc. of boiling ethyl acetate under a
reflux condenser. When the amine has dissolved the solution is rapidly cooled and stirred, whereupon the amine separates in almost white crystals. Further crops of crystals may be obtained on concentrating the solution and cooling. The last portions may be colored, but one recrystallization from
ethyl acetate gives a nearly colorless product (Note
12). The total yield of pale yellow product which melts at
126° is
200–210 g. (
82–85 per cent of the theoretical amount) (Note
13).
2. Notes
1. The
air condenser used here was 65 cm. long and of 13-mm. bore, and the
vertical water condenser, 40 cm. in length.
Cork stoppers were used, and it was found desirable to protect their exposed surfaces by coating them with water-glass, allowing these to dry, and then coating with lead foil. It is best to boil the mixture on a
sand bath and to cover with asbestos that part of the flask not immersed in the sand.
2. Technical
diphenylamine which has been distilled under reduced pressure and collected over a 5° range (
159–164°/4 mm.) is satisfactory.
4. "Natur Kupfer C" is a good catalyst, but ordinary
copper bronze may be used.
5. The time required for the completion of reaction varies with the rate of stirring. When the stirring is very vigorous most of the water comes over within twelve hours.
6. This heating should be done carefully, preferably on a sand bath, because of the danger of breaking the flask due to the caking of some undissolved
potassium carbonate.
7. In general, about 8–10 l. of aqueous distillate is required, and practically all but about
25 cc. of the nitrobenzene is recovered. It is recommended that the removal of
nitrobenzene by steam distillation be fairly complete in order to avoid a gummy residue.
9. The
hydrogen chloride is introduced through a
delivery tube at least 25 mm. in diameter and about 10 cm. under the surface of the liquid. If the gas is introduced rapidly enough and the mixture stirred occasionally there is little trouble with clogging of the delivery tube.
10. The crude
diphenylamine
may be recovered by decomposing the hydrochloride with water and filtering the mixture.
11. A large amount of
hydrogen chloride is evolved during the distillation, and some provision must be made to keep it out of the room.
A gas-absorption trap (Fig. 7 on p. 97) may be used.
12. Because of the lower solubility of
triphenylamine in
ethyl alcohol this solvent may be used advantageously in washing the crystals and in recrystallizing small amounts of the compound.
13.
N-Phenylcarbazole may be made in an analogous manner by substituting
carbazole for
diphenylamine. If stirring and heating are both very vigorous, twelve hours suffices for the reaction. The yield of purified product is about
88 per cent of the theoretical amount, and the compound melts at
88–89°. The crystals, when crushed, emit a strong violet light.
3. Discussion
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