Org. Synth. 1945, 25, 42
DOI: 10.15227/orgsyn.025.0042
ETHYL BENZALMALONATE
[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 shown
2 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
This preparation is referenced from:
Appendix
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)
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