A
2-l. three-necked flask is fitted with a
sealed mechanical stirrer, a
gas-inlet tube, and a
dry ice condenser protected from the air by a
soda-lime drying tube (Note
1). The system is flushed thoroughly with dry
ammonia, and
32.8 g. (0.84 mole) of sodium amide (Note
2) is added to the flask. The system is again flushed with
ammonia, the condenser is provided with dry ice covered by
acetone, and
1.2 l. of liquid ammonia is condensed in the flask. The gas-inlet tube is replaced with a
dropping funnel, the stirrer is started, and
118 g. (0.72 mole) of N-(2-bromoallyl)ethylamine2 is added dropwise in 20–30 minutes; during the addition, the
ammonia boils vigorously, and the color of the slurry changes from gray to black. Stirring is continued for 3 hours, and the dry ice is then allowed to evaporate. The condenser is provided with an ice-salt mixture, and the
ammonia is allowed to evaporate until the volume is reduced to about 800 ml. (Note
3).
Ethanol-free ether (200 ml.) is added rapidly through the dropping funnel, and the reaction is stopped by the slow, dropwise addition (Caution!) of 5 ml. of water. The
ammonia is allowed to evaporate overnight. Water (150 ml.) and
100 ml. of ether are added to the residue, and the mixture is stirred for 2 minutes in order to dissolve the precipitated salts. The resulting mixture, which consists of aqueous and ethereal solutions, is separated, and the aqueous phase is extracted with
75 ml. of ether. The
ether solutions are combined, dried over
sodium hydroxide (Note
4), and distilled through an
efficient low-holdup column (Note
5). The fraction with b.p.
77–80°,
n25D 1.4260–1.4268, which is
96–97% N-ethylallenimine (Note
6), weighs
30–34 g. (
48–55%). Pure (>99.5%)
N-ethylallenimine has b.p.
77–79°,
n25D 1.4281–1.4284 (Note
7) and (Note
8).