Org. Synth. 1945, 25, 44
DOI: 10.15227/orgsyn.025.0044
[3-Pentenoic acid, 2-cyano-3-ethyl-2-methyl-, ethyl ester]
Submitted by Evelyn M. Hancock and Arthur C. Cope.
Checked by H. R. Snyder and J. H. Saunders.
1. Procedure
A solution of sodium ethoxide is prepared from 9.2 g. (0.40 mole) of freshly cut sodium and 400 ml. of absolute ethanol (Note 1) in a 1-l. three-necked flask fitted with a dropping funnel, a thermometer, a mercury-sealed stirrer, and a condenser protected by a drying tube (Note 2). To the stirred solution, which is kept at −5° (conveniently by partially immersing the flask in a Dry Ice bath), 72.4 g. (0.40 mole) of ethyl (1-ethylpropylidene) cyanoacetate (p. 399) is added dropwise from the funnel during 8–10 minutes. After the mixture has been stirred for an additional 20 minutes at −5°, 62.5 g. (0.44 mole) of methyl iodide is added from the dropping funnel as rapidly as possible. The flask is heated immediately with a strong flame which is withdrawn just as the solution reaches the boiling point. The alkylation is vigorous, but the flask is not cooled unless loss of material through the reflux condenser appears imminent (Note 3). After the spontaneous reaction has subsided, the solution is refluxed until a piece of red litmus paper dipped into the liquid and subsequently moistened shows a neutral reaction (15–30 minutes).
The solution is cooled and diluted with 1 l. of water, and the ester layer is separated. The aqueous layer is extracted with four 50-ml. portions of benzene, and the combined ester and benzene extracts are washed with two 25-ml. portions of water and then distilled from a 500-ml. modified Claisen flask. The fraction (above 75 g.) which is collected at 95–118°/10 mm. is shaken mechanically for 4 hours with 100 ml. of 20% sodium bisulfite solution (Note 4). The ester layer is separated, the aqueous layer is extracted with three 25-ml. portions of benzene, and the combined ester and benzene extracts are washed with 25 ml. of water. The product remaining after removal of the benzene is distilled under reduced pressure from a 250-ml. modified Claisen flask or through a Widmer column. The yield of ester boiling at 112–113°/8 mm. is 63.5–68 g. (81–87%).
2. Notes
1. Commercial absolute ethanol is dried with sodium and ethyl phthalate1 and redistilled. The checkers obtained a considerably lower yield in a run employing ethanol dried over magnesium methoxide.
2. The various pieces of apparatus are dried in an oven and assembled rapidly in order to exclude moisture.
3. Excessive cleavage (alcoholysis) of the product is avoided by carrying out the alkylation rapidly. This procedure minimizes the time during which the product is in contact with sodium ethoxide.
4. This treatment removes ethyl (1-ethylpropylidene) cyanoacetate as a water-soluble sodium bisulfite addition product (p. 399).
3. Discussion
The above procedure illustrates a general method for preparing homologous ethyl (dialkylvinyl) alkylcyanoacetates by the alkylation of ethyl alkylidenecyanoacetates.2

References and Notes
  1. Org. Syntheses Coll. Vol. 2, 155 (1943).
  2. Cope and Hancock, J. Am. Chem. Soc., 60, 2903 (1938).

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

ethanol (64-17-5)

Benzene (71-43-2)

sodium bisulfite (7631-90-5)

sodium (13966-32-0)

sodium ethoxide (141-52-6)

Methyl iodide (74-88-4)

magnesium methoxide

ethyl phthalate

3-Pentenoic acid, 2-cyano-3-ethyl-2-methyl-, ethyl ester (53608-83-6)

ethyl (1-ethylpropylidene) cyanoacetate (868-04-2)