(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°.