Checked by William S. Johnson and Duff S. Allen, Jr..
1. Procedure
A
2-l. three-necked flask, equipped with a
sealed stirrer, a
dropping funnel and a
reflux condenser provided with a
calcium chloride drying tube, is charged with
100 g. (0.625 mole) of diethyl malonate (Note
1) and
400 ml. of commercial absolute ethanol. Stirring is started, and a solution of
35 g. of potassium hydroxide pellets (Note
2) in
400 ml. of commercial absolute ethanol is added at room temperature during a period of 1 hour. A white crystalline precipitate forms during the addition, and, after all the hydroxide has been added, stirring is continued for an additional 2 hours. After the mixture has stood overnight, it is heated to boiling on the
steam bath and filtered while hot with suction (Note
3). Precipitation of the
potassium ethyl malonate is completed by cooling the filtrate in an
ice bath. The salt is collected by suction filtration, washed with a small amount of
ether, and dried under reduced pressure at room temperature. An additional amount of the potassium salt is obtained by concentrating the mother liquors on the steam bath to about 100–125 ml. The total yield is
80–87 g. (
75–82%).
A
250-ml. three-necked flask provided with a stirrer, a dropping funnel, and a
thermometer is charged with
80 g. (0.470 mole) of potassium ethyl malonate and 50 ml. of water. The mixture is cooled to 5° with an ice bath, and
40 ml. of concentrated hydrochloric acid is added over a 30-minute period while the temperature is maintained below 10°. The mixture is filtered with suction, and the precipitate of
potassium chloride washed with
75 ml. of ether. The aqueous layer of the filtrate is separated and washed with three
50-ml. portions of ether. The combined
ether solutions are dried over anhydrous
magnesium sulfate; then most of the solvent is removed by distillation at atmospheric pressure, and the remainder under reduced pressure. Finally, the liquid residue of
monoethyl malonate is dried at 50°/1 mm. for 1 hour. The yield is
58–62 g. (
93–100%).
A
500-ml. Pyrex heavy-walled, narrow-mouthed pressure bottle is charged with
100 ml. of ether and
3.5 ml. of concentrated sulfuric acid. The solution is cooled with an ice bath to 5°, and
56 g. (0.42 mole) of monoethyl malonate and approximately
60 ml. (about 0.75 mole) of isobutylene (Note
4) are added. The bottle is immediately closed with a
rubber stopper, which is clamped or wired in place, and is shaken mechanically at room temperature overnight (Note
5). The bottle is chilled in an
ice-salt bath and then opened. The reaction mixture is poured into a
1-l. Erlenmeyer flask containing a cooled solution of
50 g. of sodium hydroxide in 200 ml. of water and 200 g. of ice. The mixture is swirled a few times and then transferred to a
separatory funnel (Note
6). The layers are separated, and the aqueous portion is extracted with two
75-ml. portions of ether. The organic layers are combined and dried over anhydrous
magnesium sulfate. The solution is concentrated in a
125-ml. round-bottomed flask (Note
7) and distilled at reduced pressure through a
10-cm. Vigreux column. The fraction distilling at
98–100°/22 mm. or
107–109°/24 mm. is collected. The yield is
42–47 g. (
53–58%),
nD25 1.4128,
nD23 1.4142.
2. Notes
1.
Diethyl malonate as supplied by the Eastman Kodak Company (white label grade) or by Abbott Laboratories may be used without further purification.
2.
Potassium hydroxide (85% minimum assay) obtained from the Mallinckrodt Chemical Works is satisfactory.
3. A steam-heated Büchner or a warmed sintered
glass funnel is recommended.
4.
Technical grade isobutylene supplied by Matheson Company was used. The
isobutylene gas is liquefied by passage into a large test tube immersed in a
Dry Ice-acetone bath.
5. For convenience, the reaction was carried out overnight. The reaction time may probably be shortened (compare the preparation of
di-tert-butyl malonate,
p. 261).
6. The mixture may be filtered, if necessary, to remove ice.
3. Discussion
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