Organic Syntheses, CV 5, 758
Submitted by S. Wawzonek, W. McKillip, and C. J. Peterson
1.
Checked by J. K. Williams, H. E. Winberg, C. L. Dickinson, and B. C. McKusick.
1. Procedure
A.
N-Benzylideneethylamine.
Benzaldehyde (466 g., 4.40 moles) is placed in a
2-l. three-necked flask equipped with a mechanical stirrer and a thermometer. The flask is cooled to 5° in an
ice bath, and
200 g. (4.44 moles) of anhydrous ethylamine (Note
1) is added to the stirred
benzaldehyde at such a rate that the temperature remains below 15°; about 50 minutes is required for the addition. The mixture is stirred for an additional 30 minutes at room temperature and allowed to stand for 1 hour.
The condenser is arranged for downward distillation, and the water is removed from the product by codistillation with
200 ml. of benzene. The residue,
N-benzylideneethylamine, is purified by distillation through a
25-cm. Fenske column; b.p.
52–53° (4.5 mm.);
n23D 1.5400; weight
470–523 g. (
80–89%) (Note
2).
B.
N-Methylethylamine N-Benzylideneethylamine. (133 g., 1.00 mole) is heated with
156 g. (1.10 moles) of methyl iodide (Note
3) in a
300-ml. pressure bomb at 100° for 24 hours (Note
4). The bomb is cooled to 50° (Note
5), and the dark, viscous oil is poured into a
1-l. beaker containing 200 ml. of water. The bomb is rinsed with three 50-ml. portions of water, and the washings are combined with the main solution. The resulting mixture is heated with manual stirring on a
steam bath for 20 minutes and then cooled in an
ice bath to room temperature. The resulting mixture is extracted with two
75-ml. portions of ether (Note
6). The
ether layer is washed with two 50-ml. portions of water, and the washings are combined with the main aqueous layer, which is then heated at 100° on a steam bath for 20 minutes to remove traces of
ether.
For the liberation of
N-methylethylamine, a
1-l. Claisen flask is equipped with a 250-ml. separatory funnel and an efficient condenser for distillation. The receiver is cooled with a mixture of
acetone and dry ice (Note
7). A solution of
100 g. (2.5 moles) of sodium hydroxide in 100 ml. of water is added to the flask and kept at about 100° by heating on a steam bath. The aqueous solution of
N-methylethylamine hydriodide is added to this solution through the separatory funnel in the course of 1.5 hours. After the addition is complete, the final solution is heated for an additional 30 minutes. Crude
N-methylethylamine, b.p.
30–70°, collects in the cooled receiver. It is purified by distillation from
25 g. of solid potassium hydroxide in a
250-ml. modified Claisen flask fitted with a 25-cm. Fenske column and a receiver cooled by dry ice and acetone.
N-Methylethylamine is collected at
34–35°; weight
49–55 g. (
83–93%);
n25D 1.3830.
2. Notes
1. The
ethylamine is cooled to 5° to prevent loss by evaporation. Addition is made directly from the bottle with intermittent cooling in an ice bath.
2. The aldimine need not be distilled but can be used directly in the next step.
5. The pressure bomb is opened while still warm (50°). If the bomb is allowed to cool below this temperature, the product solidifies and removal becomes a problem.
7. Because of the low boiling point of
N-methylethylamine, there must be efficient cooling or a portion of the product will be lost.
3. Discussion
4. Merits of the Preparation
The method gives better yields, utilizes more readily available starting materials, and is much less laborious than the hydrolysis of N-methyl-N-alkylarenesulfonamides and
p-nitroso-N, N-dialkylanilines, or the
lithium aluminum hydride reduction of alkyl isocyanates. Compared to the closely related procedure of Lucier, Harris, and Korosec,
12 in which the N-benzylidenealkylamine is treated with dialkyl sulfate at atmospheric pressure, the present procedure tends to give higher yields and purer products, but it is less convenient because of the need for a pressure vessel.
This preparation is referenced from:
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