Organic Syntheses, CV 4, 298
Submitted by Wayne Feely and V. Boekelheide
1.
Checked by Max Tishler, Barbara P. Birt, and Arthur A. Patchett.
1. Procedure
A solution of
108 g. (0.5 mole) of diethyl ethoxymethylenemalonate (Note
1) in
100 ml. of commercial absolute alcohol is placed in an apparatus for high-pressure hydrogenation together with
10 g. of Raney nickel catalyst (Note
2). The pressure in the bomb is raised to 1000–1500 lb. with
hydrogen, and the temperature is adjusted to 45° (Note
3). The bomb is shaken, and the reaction is allowed to proceed for 12–20 hours, during which time
0.5 mole of hydrogen is absorbed.
The apparatus is allowed to cool to room temperature, the pressure is released, and the catalyst is removed by filtration. Concentration of the filtrate under reduced pressure at room temperature yields a colorless oil (Note
4).
The residual oil is transferred to a distillation flask (Note
5), and the flask is carefully warmed with a small flame (Note
6). After a fore-run of
ethanol is collected, the variable transformer controlling the heating tape is set at a voltage to give an internal temperature in the distilling head of 80–100° before distillation. The flask is then heated to effect slow distillation at atmospheric pressure. About
10–13 g. of fore-run is collected before the temperature of the distillate vapor reaches 200°. The main fraction (
68–71 g.,
79–82%) is collected between
200° and 216° as a colorless oil. For most purposes, the fore-run is sufficiently pure that it can be combined with the main fraction to give an over-all yield of
78–81 g. (
91–94%) (Note
7).
Diethyl methylenemalonate polymerizes on standing to a white solid, from which the monomer can be recovered by slow distillation. The
diethyl methylenemalonate should be distilled just prior to use (Note
8).
2. Notes
2.
Raney nickel catalyst can be prepared by the method of Mozingo.
3 The submitters used
Raney nickel catalyst obtained commercially from the Gilman Paint and Varnish Company, Chattanooga, Tennessee.
4. This oil,
n20D 1.4254, is presumably
diethyl ethoxymethylmalonate, as evidenced by its infrared and ultraviolet absorption spectra. It is relatively stable and can be stored at room temperature without change. If the concentration of the filtrate under vacuum is carried out by heating on a
steam bath instead of by keeping it at room temperature, the
diethyl ethoxymethylmalonate undergoes elimination of
ethanol to some extent, giving
diethyl methylenemalonate directly. The yield of
diethyl methylenemalonate obtained eventually is not altered by this procedure.
5. The distillation apparatus is shown in
f.htmig. 7. The upper part of the flask and the
short column are wrapped in electrical heater tape, which is operated during distillation of the product.
Fig. 7.
6. The elimination of
ethanol is slightly exothermic. It is advisable to heat the flask cautiously with a small flame until the reaction starts and then to remove the flame until the reaction subsides.
7. The fore-run has a refractive index (usually about
n22D 1.4154) lower than that of the main fraction (about
n22D 1.4250). The combined fractions show refractive indices in the range
n22D 1.4210–1.4259.
8. When the solid polymer from the above preparation was slowly distilled to recover
diethyl methylenemalonate, there was obtained
57 g. of colorless oil, b.p.
210–216° /730 mm.,
n20D 1.4220.
3. Discussion
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