Submitted by Ralph Mozingo and J. H. McCracken.
Checked by C. F. H. Allen and Joseph Dec.
1. Procedure
In a
2-l. flask, fitted with a
rubber stopper carrying a soda-lime drying tube and a glass tube reaching almost to the bottom, is placed
325 g. (420 ml.) of absolute ethanol. The whole is then tared and placed in an
ice bath, and the
inlet tube is connected to a source of dry methylamine.
The
methylamine generator consists of a
1-l. flask fitted with a
dropping funnel and outlet tube, which in turn is connected to a
25-cm. drying tower containing soda-lime, followed by a
1-l. safety trap (Note
1). In the flask is placed
200 g. of technical sodium hydroxide flakes, and
263 g. of a 33–35% solution of methylamine in water (Note
2) is dropped in slowly at such a rate that an even current of gas is evolved. When the addition has been completed and the gas bubbles very slowly into the
ethanol, the flask and contents are removed and weighed; the increase should be 84–86 g. (2.71–2.77 moles) (Note
3).
The flask is reimmersed in the ice bath, and
900–925 g. (5.4–5.5 moles), depending upon the weight of methylamine, of a 60% solution of ethyl acrylate in ethanol (Note
4) is added in portions of about 100 ml. at such a rate that the temperature of the mixture does not rise above 40°; this requires about 10 minutes. After each addition the flask is stoppered to exclude moisture. When all the ester has been added the flask is closed by a
rubber stopper and allowed to stand 6 days (Note
5).
Most of the
ethanol is removed by distillation (1.5 hours) on a
steam bath, and the residue is transferred to a
modified Claisen flask and distilled. The fraction boiling below 50°/20 mm. (Note
6) is removed with the aid of a
water pump, and the residue is distilled using an
oil pump (at 3 mm. pressure) (Note
7). The portion boiling at
105–108°/3 mm. (Note
8) is collected as
di-β-carbethoxyethylmethylamine (Note
9); it amounts to
519–550 g. (
83–86%) (Note
10).
2. Notes
1. The safety trap is important, since the
ethanol tends to suck back easily.
2. Solutions of
methylamine in water are obtainable from Eastman Kodak Company (33%) and Rohm and Haas Company (35%).
3. It is much more convenient to use the amount of
methylamine secured than to try to collect a predetermined weight.
4. The
ethyl acrylate (60% solution in ethanol) is available from the Rohm and Haas Company. The solution, containing a polymerization inhibitor, is used without treatment. The inhibitor must not be removed.
5. If the time is shortened, the yield is correspondingly decreased.
6. Most of this distillate comes over with the
oil-bath temperature at 75°; the temperature is finally raised to 150°. The fractionating arm of the Claisen flask used was wrapped with asbestos cord.
7. Any
ethyl N-methyl-β-aminopropionate formed comes over in the first or middle fraction (6–8 ml.). The middle fraction is obtained as the fraction boiling up to 105°/3 mm., on changing from the water pump to an oil pump. The oil bath is cooled to 100° before applying the higher vacuum.
8. The observed boiling points vary with the particular apparatus used.
9. Since the ester decomposes very slightly during distillation, the oil pump should be protected from
ethyl acrylate and
methylamine by a
Dry Ice trap. The distillation should not be interrupted.
3. Discussion
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