Submitted by P. L. Salzberg and J. V. Supniewski.
Checked by F. C. Whitmore and H. C. Benedict, Jr.
1. Procedure
(
A)
Potassium Phthalimide.—In a
2-l. round-bottomed flask fitted with a
reflux condenser are placed
80 g. (0.54 mole) of phthalimide (Note
1) and
1600 cc. of absolute alcohol (p. 249). The mixture is gently boiled for about fifteen minutes or until no more of the
phthalimide dissolves (Note
2). The hot solution is decanted from any solid into a specially prepared solution of
30.5 g. (0.54 mole) of potassium hydroxide (Note
3). A precipitate of
potassium phthalimide separates at once. The mixture is stirred and cooled quickly to room temperature, and the precipitate is filtered with suction. To the alcoholic mother liquors a second
80-g. portion of phthalimide is added, and the entire process is repeated. The two crops of crystals are united (Note
4) and washed with
200 cc. of acetone to remove any unchanged
phthalimide. The yield of air-dried
potassium phthalimide is
160–180 g. (
80–90 per cent of the theoretical amount).
(
B)
β-Bromoethylphthalimide.—In a
1-l. two-necked round-bottomed flask fitted with an
efficient stirrer and a
reflux condenser are placed
150 g. (0.81 mole) of potassium phthalimide and
450 g. (2.4 moles) of ethylene dibromide (Note
5). The stirrer is started and the mixture is heated for about twelve hours in an
oil bath maintained at 180–190°. The condenser is then set for distillation, and the excess of
ethylene dibromide is distilled under reduced pressure. The recovery of the
bromide amounts to
290–295 g. (Note
6).
The crude
bromoethylphthalimide is extracted from the
potassium bromide by refluxing with
300 cc. of alcohol (98–100 per cent) (Note
7) until the dark oil is entirely dissolved. This requires about one-half. hour. The hot solution is filtered with suction, and the residue of salt is washed with a little hot alcohol. The alcohol is distilled under reduced pressure, and the dry residue is refluxed with
500 cc. of carbon disulfide for about fifteen minutes in order to separate the soluble
bromoethylphthalimide from the insoluble
diphthalimidoethane (Note
8). The warm solution is filtered with suction. The
carbon disulfide is distilled under diminished pressure (Note
9). The
bromoethylphthalimide remains as light tan crystals which melt at
78–80°. The yield is
140–160 g. (
69–79 per cent of the theoretical amount).
The product thus obtained is pure enough for most purposes. However, a purer product may be obtained by recrystallization from dilute alcohol in the presence of
decolorizing carbon. When 50 g. of crude product is dissolved in
200 cc. of 75 per cent alcohol, boiled for about ten minutes with
5 g. of decolorizing carbon (Norite), filtered, and the solution cooled to 0°, 40 g. of white product is obtained. The recrystallized product melts at
80–81°. A second recrystallization raises the melting point to
82–83°.
2. Notes
2. The crude product always contains a small amount of material insoluble in alcohol.
3. It is convenient to prepare enough
potassium hydroxide solution for the two precipitations at one time. This solution is prepared by dissolving 61 g. of
potassium hydroxide in 60 cc. of water. To this solution is then added
180 cc. of absolute alcohol. One-half of the resulting solution is used for each
80-g. portion of phthalimide.
4. After the first crop has been filtered, most of it should be removed and the second crop should be filtered through the same paper. The alcoholic filtrate on distillation yields about
1500 cc. of 98 per cent alcohol.
6. The last 15 to 20 g. of this recovered product distils very slowly.
7. The alcohol recovered from the preparation of the
potassium phthalimide may be used for this extraction.
9. If the
carbon disulfide is distilled at ordinary pressures, the residue melts and turns very dark. The crude yield is not lowered, but the purification is made more difficult.
3. Discussion
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