Organic Syntheses, Coll. Vol. 5, p.541 (1973); Vol. 44, p.53 (1964).
Caution! This preparation should be carried out in a good hood
to avoid exposure to ammonia
. The operator should wear rubber gloves and protective goggles because 2-haloallylamines and ethylenimines can cause severe skin and eye irritation.
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°
1.4260–1.4268, which is 96–97% N-ethylallenimine (Note 6)
, weighs 30–34 g.
). Pure (>99.5%) N-ethylallenimine
has b.p. 77–79°
1.4281–1.4284 (Note 7)
and (Note 8)
The glassware should be dried in an oven
before use, and water must be rigorously excluded from the reaction mixture.
The sodium amide was obtained from Roberts Chemical Co., Nitro, West Virginia
About 1.5–2.5 hours is required; stirring is continued and ice is prevented from forming on the outside of the flask. The checkers used an inner-spiral condenser cooled by ice water.
solution and fractions taken during the subsequent distillation may be assayed by gas-liquid partition chromatography on a 0.8-cm. × 200-cm. column
heated at 120° and packed with nonyl phthalate
supported on ground firebrick.
The submitters concentrated the dry ether
solution to a volume of 80–100 ml. by distillation through a 1.0-cm. × 40-cm. column
packed with glass helices and equipped with a total-reflux head. p-Xylene
(10 ml.) was added to the residue, and this solution was fractionated through a 0.8-cm. × 30-cm. Podbielniak-type column
fitted with a total-reflux head. The submitters recommend that, during distillation of the concentrated solution, a slow stream of nitrogen
be passed through the boiling liquid to minimize the formation of dark, tarry products. The checkers used a 1-cm. × 100-cm. spinning-band column
(Nester and Faust Co.) for the distillation of N-ethylallenimine
and were able to obtain material of 99% purity (Note 7)
The submitters obtained essentially pure (>99.5%) N-ethylallenimine
by redistilling 30 g.
or more of the 96–97%
pure product through the Podbielniak column
and rejecting the first 10–20% and the last 20% of the distillate. The yield of pure N-ethylallenimine
is 18–21 g.
). Pure N-ethylallenimine
has also been obtained in comparable yields by (a
) distilling the combined concentrated solution from the equivalent of three runs through a 1.3-cm. × 100-cm. column
packed with glass helices and equipped with a total-reflux head, and (b
) treating the crude distillate with lithium aluminum hydride
as described for the purification of N-propylallenimine
Samples of pure N-ethylallenimine
and other allenimines have been stored at 0° for well over a year with no significant deterioration. Caution! N-Alkylallenimines, even as dilute solutions in aqueous ethanol, are rapidly destroyed by acid.4,5
Therefore concentrated solutions of N-alkylallenimines should not be allowed to come in contact with acid because of the possibilities of violent decomposition.
4. Merits of the Preparation
This is a general method for making N-alkylallenimines, and the following ones have been made in this way: N-methyl-,6
and N-(3,5,5-trimethylhexyl)-.4 N-t-Butylallenimine6
have also been prepared by this method, but with sodium amide
mole ratios of 1.75 and 2.1, respectively. This method has been used for the preparation of pure N-alkylpropargylamines from 2-chloroallylamines.6,7
The optimum sodium amide
ratio for the preparation of N-alkylpropargylamines is 2.1.
This preparation is referenced from:
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