Org. Synth. 1948, 28, 60
DOI: 10.15227/orgsyn.028.0060
[Malonic acid, ethoxymethylene-, diethyl ester]
Submitted by W. E. Parham and L. J. Reed1.
Checked by J. R. Roland, C. W. Todd, and R. S. Schreiber.
1. Procedure
A mixture of 1000 g. (6.75 moles) of ethyl orthoformate, 1260 g. (12.3 moles) of acetic anhydride, 960 g. (6.0 moles) of ethyl malonate, and 0.5 g. of anhydrous zinc chloride is prepared in a 5-l. three-necked flask equipped with a thermometer, a gas inlet tube, and a 12-in. column packed with Berl Saddles (Note 1). The column is attached to a still head and condenser. The contents of the flask are well agitated for 5 minutes by a stream of dry air and then heated (Note 2) as follows: 102–115° for 2.5 hours, 115–127° for 7 hours [after the eighth hour of heating, 250 g. (2.45 moles) of acetic anhydride and 200 g. (1.35 moles) of ethyl orthoformate are added], 127–145° for 2 hours, and 145–155° for 2 hours (Note 3). At the end of 13.5 hours of heating the mixture is cooled to room temperature and filtered (Note 4). The filtrate is distilled under reduced pressure (15–20 mm.) until the temperature at the still head reaches 100° (Note 5). The distillation is then continued under lower pressure (0.25 mm.). The yield of ethyl ethoxymethylenemalonate, b.p. 108–110°/0.25 mm. (Note 6), is 650–780 g. (50–60% based on the ethyl malonate used).
2. Notes
1. The use of this column prevents loss of acetic anhydride during the heating process and permits volatile products formed during the reaction to be removed by distillation. The checkers used a 1 by 12 in. column packed with 6 by 6 mm. glass rings.
2. The zinc chloride dissolves, and a chlorine-free crystalline precipitate soon separates. The checkers observed only traces of this precipitate.
3. The final heating is necessary to convert unchanged ethyl diethoxymethylmalonate, an intermediate in the reaction, into ethyl ethoxymethylenemalonate. This intermediate is difficult to separate from ethyl ethoxymethylenemalonate by distillation, and it is important that it be converted as completely as possible during the heating process.
4. The mixture is filtered through a fluted filter paper to remove suspended zinc salts.
5. Unchanged ethyl malonate (as much as 15% of the amount used) can be obtained by redistillation of the fraction boiling at 70–100°/17 mm.
6. Since ethyl diethoxymethylmalonate is difficult to separate from ethyl ethoxymethylenemalonate by distillation, it is necessary to follow the course of the distillation by observation of the change in refractive index instead of the change in boiling point. After a low-boiling fraction is collected, there is obtained an intermediate fraction (nD20 1.4142–1.4580), the size of which depends upon the amount of ethyl diethoxymethylmalonate present. Under the best of conditions it amounts to 15 g. In each of three runs, the checkers obtained about 300–400 g. of material having a refractive index in this range. The ethyl ethoxymethylenemalonate was collected at nD20 1.4580–1.4623. The checkers used a 5-in. Vigreux column and observed that at the low pressures the boiling point of the distillate in several runs was about 10° lower than that reported by the submitters. For example, in one run at 0.25 mm. (gauge pressure) the boiling point of the distillate never rose above 97.2°; however, the refractive indices of twelve 50-ml. fractions taken in the course of this distillation were all in the proper range, nD20 1.4612–1.4623. Interruption of the heating during the reaction period should be avoided. In an experiment in which the heating was discontinued after about 8 hours and resumed the next day the yield was about 50%.
3. Discussion
Ethyl ethoxymethylenemalonate has been prepared by heating ethyl orthoformate, ethyl malonate, and acetic anhydride in the presence of zinc chloride.2,3 A higher yield of purer product is obtained by the method described above,4 which is a modification of the Claisen procedure.
This preparation is referenced from:

References and Notes
  1. Work done under contract with the Office of Scientific Research and Development.
  2. Claisen, Ber., 26, 2729 (1893); Ann., 297, 76 (1897).
  3. Wheeler and Johns, Am. Chem. J., 40, 237 (1908).
  4. Fuson, Parham, and Reed, J. Org. Chem., 11, 194 (1946).

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

acetic anhydride (108-24-7)

zinc chloride (7646-85-7)

Ethyl orthoformate

ethyl malonate (1071-46-1)

ethyl ethoxymethylenemalonate

Malonic acid, ethoxymethylene-, diethyl ester (87-13-8)

ethyl diethoxymethylmalonate