A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1945, 25, 42
DOI: 10.15227/orgsyn.025.0042
[Malonic acid, benzal-, diethyl ester]
Submitted by C. F. H. Allen and F. W. Spangler.
Checked by R. L. Shriner and Fred W. Neumann.
1. Procedure
In a 1-l. round-bottomed flask, which is fitted with a Clarke-Rahrs column1 with a unit for removing water and surmounted by a reflux condenser, are placed 100 g. (0.63 mole) of ethyl malonate (Note 1), about 72–76 g. of commercial benzaldehyde (Note 2), 2–7 ml. of piperidine (Note 3), and 200 ml. of benzene. The mixture is refluxed vigorously in an oil bath at 130–140° until no more water (total, 12–13 ml.) is collected; this operation requires 11–18 hours. After the mixture has been cooled, 100 ml. of benzene is added and the solution is washed with two 100-ml. portions of water, with two 100-ml. portions of 1 N hydrochloric acid, and then with 100 ml. of a saturated solution of sodium bicarbonate. The aqueous wash solutions are shaken with a single 50-ml. portion of benzene, the benzene extract is added to the original organic layer, and the organic solution is dried with 30 g. of anhydrous sodium sulfate. After the benzene has been removed under reduced pressure on a steam bath, the residue is distilled under reduced pressure from a 250-ml. modified Claisen flask well wrapped with asbestos. The yield of colorless ethyl benzalmalonate boiling at 140–142° /4 mm. (Note 4) is 137–142 g. (89–91%) (Note 5).
2. Notes
1. B.p. 94–96° /16mm. The checkers used redistilled ethyl malonate.
2. Commercial benzaldehyde which contains 2–8% of benzoic acid is eminently satisfactory. The acid content is determined (conveniently by titration of a sample in neutral ethanol with standard alkali), and a quantity of aldehyde containing 70 g. (0.66 mole) of benzaldehyde is used. The checkers used 76 g. of commercial benzaldehyde which contained 8% of benzoic acid. If pure benzaldehyde is employed, then 2 g. of benzoic acid should be added. It has been shown2 that piperidine salts and not the free base act as the catalyst in the Knoevenagel reaction. The checkers obtained only a 71% yield with benzaldehyde containing less than 0.2% of benzoic acid.
3. The amount of piperidine that is employed depends on the benzoic acid content of the aldehyde; it should be slightly in excess of that required to neutralize the benzoic acid. About 1.2 ml. of piperidine per gram of acid is satisfactory.
4. Another boiling point is 179–181° /10 mm. The boiling points reported for ethyl benzalmalonate vary widely. The temperature observed depends on the degree of superheating and the rapidity of distillation.
5. Methyl benzalmalonate (b.p. 143–146° /2 mm., 169–171° /10 mm.) can be prepared in the same manner and in the same apparatus in yields of 90–94%.
3. Discussion
Ethyl benzalmalonate has been prepared by the esterification of benzalmalonic acid in the presence of concentrated sulfuric acid;3 by the action of benzal chloride on sodiomalonic ester;4 by the condensation of benzaldehyde and malonic ester in the presence of hydrogen chloride,5,6 acetic anhydride,7 alcoholic piperidine or ammonia,8 or aluminum chloride,9 and by the action of phenylmagnesium bromide on hydroxymethylene malonic ester.10

References and Notes
  1. Clarke and Rahrs, Ind. Eng. Chem., 18, 1092 (1926).
  2. Kuhn, Badstubner, and Grundmann, Ber., 69, 98 (1936).
  3. Stuart, J. Chem. Soc., 47, 158 (1885).
  4. Avery and Bouton, Am. Chem. J., 20, 510 (1898).
  5. Claisen, Ber., 14, 348 (1891).
  6. Claisen and Crismer, Ann., 218, 131 (1883).
  7. Knoevenagel, Ber., 31, 2591 (1898); Gravel, Nat. canadien, 57, 181 (1931) [C. A., 28, 169 (1934)].
  8. Ger. pat. 97,734 [Frdl., 5, 906 (1898–1900)].
  9. Breslow and Hauser, J. Am. Chem. Soc., 62, 2385 (1940).
  10. Reynolds, Am. Chem. J., 44, 314 (1910).

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

sodiomalonic ester

hydroxymethylene malonic ester

ethanol (64-17-5)

sulfuric acid (7664-93-9)

hydrogen chloride,
hydrochloric acid (7647-01-0)

ammonia (7664-41-7)

Benzene (71-43-2)

acetic anhydride (108-24-7)

sodium bicarbonate (144-55-8)

sodium sulfate (7757-82-6)

Benzoic acid (65-85-0)

benzaldehyde (100-52-7)

aluminum chloride (3495-54-3)

piperidine (110-89-4)

Phenylmagnesium bromide (100-58-3)

ethyl malonate (1071-46-1)

Ethyl benzalmalonate

benzal chloride (98-87-3)

Malonic acid, benzal-, diethyl ester (5292-53-5)

Methyl benzalmalonate

benzalmalonic acid (584-45-2)