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Org. Synth. 1952, 32, 52
DOI: 10.15227/orgsyn.032.0052
DIETHYL Δ2-CYCLOPENTENYLMALONATE
[2-Cyclopentene-1-malonic acid, diethyl ester]
Submitted by Robert Bruce Moffett1
Checked by R. T. Arnold and George P. Scott.
1. Procedure
Nine hundred and twenty-five milliliters of absolute ethanol (Note 1) is placed in a 2-l. three-necked round-bottomed flask, fitted with a mercury or glycerin-sealed stirrer (Note 2), dropping funnel, and reflux condenser. To this is added 46 g. (2 g. atoms)2 of freshly cut sodium, a few pieces at a time and at such a rate that the reaction proceeds rapidly but the solvent does not reflux too vigorously. When most of the sodium has dissolved, a calcium chloride drying tube is fitted to the top of the condenser and 320 g. (2 moles) of redistilled diethyl malonate is added from the dropping funnel. Then 205 g. (2 moles) of 3-chlorocyclopentene (p. 42) (Note 3) is added at such a rate that a gentle reflux is maintained. Toward the end of the addition, it is desirable to test the reaction mixture with pH test paper, and the addition should be stopped if the solution becomes acidic.
When the addition is complete, the condenser is set downward for distillation, the stirring is continued, and most of the ethanol is removed by distillation on a steam bath (Note 4). After cooling, the reaction mixture is diluted with sufficient water to dissolve the salt, and the layers are separated. The aqueous layer is extracted with 50 ml. of ether. The ethereal solution is added to the ester, and the resulting solution is washed with saturated salt solution and dried over anhydrous magnesium sulfate. The ethereal solution is transferred to a Claisen flask, the solvent is evaporated, and the product is distilled under reduced pressure. The fraction boiling at about 85–140°/12 mm. is collected and redistilled through an efficient fractionating column (Note 5). The product distils at 130°/12 mm. (Note 6). The yield is about 276.5 g. (61%); n20D 1.4536.
2. Notes
1. The preparation of absolute ethanol has been described earlier.3
2. The glycerin-sealed stirrer has been described earlier.2
3. It is not necessary to use redistilled 3-chlorocyclopentene; however, if large amounts of impurities are present, difficulty may be encountered in obtaining a pure product.
4. If a glycerin-sealed stirrer is used, the rate of solvent evaporation may be accelerated by means of gentle water-pump suction.
5. Careful fractionation is necessary in order to secure a pure product. The submitter used a 12-in. column packed with 1/8-in. glass helices. The fore-run should be redistilled to separate any ester it may contain.
6. Other boiling points are 140°/18 mm.; 97°/1 mm.
3. Discussion
Diethyl Δ2-cyclopentenylmalonate has been prepared by the alkylation of malonic ester with 3-chlorocyclopentene.4,5,6,7,8

References and Notes
  1. The Upjohn Company, Kalamazoo, Michigan.
  2. Org. Syntheses Coll. Vol. 3, 368 (1955).
  3. Org. Syntheses Coll. Vol. 1, 259 (1941).
  4. Noller and Adams, J. Am. Chem. Soc., 48, 2444 (1926).
  5. Perkins and Cruz, J. Am. Chem. Soc., 49, 518 (1927).
  6. Wagner-Jauregg and Arnold, Ann., 529, 274 (1937).
  7. Horclois, Chim. & ind. (Paris), 31, 357 (Special No., April, 1934).
  8. Buu-Hoï and Cagniant, Bull. soc. chim. France, [5] 9, 99 (1942).

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

Diethyl Δ2-cyclopentenylmalonate

ethanol (64-17-5)

ether (60-29-7)

sodium (13966-32-0)

diethyl malonate (105-53-3)

2-Cyclopentene-1-malonic acid, diethyl ester (53608-93-8)

magnesium sulfate (7487-88-9)

3-Chlorocyclopentene (96-40-2)