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Org. Synth. 1922, 2, 75
DOI: 10.15227/orgsyn.002.0075
PHTHALIMIDE
Submitted by W. A. Noyes and P. K. Porter.
Checked by H. T. Clarke and J. H. Bishop.
1. Procedure
(A) In Pyrex 5-l. round-bottomed flask is placed a mixture of 500 g. (3.4 moles) of phthalic anhydride and 400 g. (444 cc., 6.6. moles) of 28 per cent aqueous ammonia. The flask is fitted with an air condenser not less than 10 mm. in diameter and is then slowly heated with a free flame until the mixture is in a state of quiet fusion at a temperature of about 300° (Note 1). It requires about one hour before all the water has gone and about one and one-half to two hours before the temperature of the reaction mixture reaches 300° and the mixture is a homogeneous melt. It is advisable, during the heating, to shake the flask occasionally; some material sublimes into the condenser and must be pushed down with a glass rod. The hot reaction mixture is now poured out into a crock, covered with a paper to prevent loss by sublimation, and allowed to cool (Note 2). The product is practically pure without further treatment, and melts at 232–235° (Note 3). The yield is 470–480 g. (95–97 per cent of the theoretical amount) (Note 4).
(B) Phthalimide may also be made by fusing 500 g. (3.4 moles) of phthalic anhydride and 500 g. (4.4 moles) of ammonium carbonate which has been previously ground in a mortar. The subsequent procedure is the same as when aqueous ammonia is used. Frequent shaking is necessary, and the sublimed material must be pushed back occasionally into the reaction flask. About two hours are required for completion.
2. Notes
1. On a large scale, it would be advisable to collect the small amount of ammonia given off during the reaction.
2. If desired, the product obtained by pouring the reaction mass into the crock may be treated with hot water to soften the cake, broken up with a glass rod, transferred to a flask, and boiled with water for a few minutes. This treatment, however, is quite unnecessary; for all preparative purposes, the crude cake, as it is obtained, may be ground up and used directly.
3. Phthalimide may be recrystallized from water, but only about 4 g. of phthalimide will dissolve in a liter of boiling water. It may also be crystallized from alcohol, in which solvent it dissolves to the extent of five parts in a hundred at boiling temperature.
4. Several smaller runs of 25 g. of phthalic anhydride gave the same percentage yield.
3. Discussion
Phthalimide can be prepared by heating ammonium phthalate,1 by heating acid ammonium phthalate,2 and by passing dry ammonia over heated phthalic anhydride.3 It was found that the last of these methods was by no means easy to bring about: dry phthalic anhydride is apparently only superficially affected by the dry ammonia, and it was difficult to introduce sufficient heat into the loose mass of crystals to initiate reaction.
This preparation is referenced from:

References and Notes
  1. Laurent, Ann. 19, 47 (1836); Ann. 41, 110 (1842); Marignac, Ann. 42, 220 (1842); Wagner, Jahresber. 549 (1868); Cohn, Ann. 205, 300 (1880); Landsberg, Ann. 215, 181 (1882).
  2. Marignac, Jahresber. 590 (1847–48).
  3. Kuhara, Am. Chem. J. 3, 29 (1881).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

acid ammonium phthalate

alcohol (64-17-5)

ammonium carbonate (506-87-6)

ammonia (7664-41-7)

phthalic anhydride (85-44-9)

Phthalimide (85-41-6)

ammonium phthalate (523-24-0)