Organic Syntheses, CV 5, 376
Submitted by Walter H. Hartung, Jan H. R. Beaujon, and George Cocolas
1.
Checked by John C. Sheehan and Robert W. Parsons, Jr..
1. Procedure
A.
Diethyl aminomalonate. An ethereal solution
(about 150 ml.) of diethyl isonitrosomalonate prepared from
50 g. of diethyl malonate (Note
1) is washed with
80-ml. portions of 1% sodium bicarbonate solution until the final washing has a distinct yellow color (Note
2). The ethereal solution is dried over
40 g. of anhydrous sodium sulfate in a refrigerator overnight and then filtered into a tared
round-bottomed flask. The solvent is removed under reduced pressure at a temperature below 30° (
water bath). The weight of the residue in one case was 59.6 g. Assuming complete conversion of the
0.312 mole of diethyl malonate to
diethyl isonitrosomalonate, a 0.1-mole aliquot (19.1 g.) of the residue is placed in a
500-ml. reduction bottle provided for the
Parr Hydrogenator (Note
3). To this is added
100 ml. of absolute alcohol and
3 g. of 10% palladium-on-charcoal catalyst (Note
4). The bottle is placed in a hydrogenator, and the system is flushed three or four times with
hydrogen. With the initial reading on the pressure gauge at 50–60 lb., the bottle is shaken until no further drop in pressure is observed (about 15 minutes).
The catalyst is removed by filtration, using an absolute alcohol wash, and the clear filtrate is concentrated under reduced pressure at a temperature below 50° (water bath). As
diethyl aminomalonate is not so stable as its salts, the crude product is converted directly to
diethyl aminomalonate hydrochloride (Note
5).
2. Notes
2. About six washings are required. It may be necessary to add a total of 50 ml. of
ether during the first three washings and 20 ml. during the final washing to facilitate breaking of the interphase emulsions. In each case, after partial separation of phases has occurred,
ether is added and the
separatory funnel is swirled gently until the interphase clears. The washing process requires about 1.5 hours.
3. As
diethyl isonitrosomalonate may decompose with explosive violence on heating, further purification by distillation is not recommended.
4. The checkers used
10% palladium-on-charcoal catalyst obtained from Baker and Company, Inc., 113 Astor Street, Newark, New Jersey.
5. According to the submitters,
diethyl aminomalonate may be purified by distillation, b.p.
116–118°/12 mm. or
122–123°/16 mm.;
nD16 = 1.4353;
d1416 = 1.100.
6.
Hydrogen chloride is dried by passage through a train of two gas washing bottles containing concentrated
sulfuric acid. A
10-mm. tube through which the
hydrogen chloride is passed is placed just over the stirring liquid, instead of under the surface, to prevent clogging of the tube by the bulky precipitate which is formed.
The checkers found magnetic stirring satisfactory. More
ether may have to be added to prevent the heavy slurry from stopping the stirrer.
7. A
medium-porosity sintered-glass funnel was used by the checkers.
3. Discussion
Diethyl aminomalonate is a useful intermediate, lending itself to N-acylation;
3,7 the N-acyl derivatives may be alkylated by procedures as established for syntheses via malonic ester.
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