Org. Synth. 1926, 6, 36
DOI: 10.15227/orgsyn.006.0036
ETHYL ACETOACETATE
[Acetoacetic acid, ethyl ester]
Submitted by J. K. H. Inglis and K. C. Roberts.
Checked by C. S. Marvel and F. E. Kendall.
1. Procedure
In a 2-l. round-bottomed flask, fitted with an efficient reflux condenser, are placed 500 g. (531 cc., 5.7 moles) of ethyl acetate (Note 1), and 50 g. (2.2 atoms) of clean sodium wire or finely sliced sodium (Note 2) is added. The reaction is at first quite slow, and must be started by warming on a water bath (Note 3). After the reaction is once started it proceeds vigorously and cooling is then necessary in order to avoid loss of material through the condenser. When the rapid reaction slows down, the reaction mixture is heated on a water bath until the sodium has completely dissolved. This usually requires about one and one-half hours. At this stage the reaction mixture should be a clear red liquid with a green fluorescence.
This solution is then cooled and made slightly acid by adding about
275 cc. of 50 per cent acetic acid (Note 4). Salt is added if necessary to cause the ester to separate. The ester layer is separated, dried over
calcium chloride, and fractionally distilled under reduced pressure from a
modified Claisen flask (p. 130).
The yield of ester boiling at 76–80°/18 mm. is 105–110 g. (28–29 per cent of the theoretical amount based on the ethyl acetate) (Note 5).
2. Notes
1.
The grade of
ethyl acetate used is very important. It must be entirely free from water and should contain about
2–3 per cent of alcohol. The
absolute ethyl acetate of the U. S. Industrial Alcohol Company is satisfactory for use. If this grade is not available, ordinary
ethyl acetate may be purified by washing it with twice its volume of water and drying over fused
potassium carbonate, from which it is decanted, and used directly. The
ethyl acetate purified in this way contains enough
ethyl alcohol to allow the reaction to run well. The
ethyl acetate in the wash water may be recovered by distilling through a
short column from a
steam cone until the vapors reach a temperature of 72°. Dry
ethyl acetate containing
2–3 per cent of alcohol has a boiling point range of 2 to 3°.
If the ester is dry enough to use in this reaction it will not give a gelatinous mass of sodium hydroxide when treated with a little sodium.
2.
Sodium wire and finely sliced
sodium are equally good to use in this reaction. It is important to avoid exposure of the
sodium to the air which converts part of it into
sodium hydroxide.
3.
It is convenient to arrange the water bath so that it may be heated by passing in steam or cooled by running in cold water.
4.
It is advisable to avoid a large excess of
acetic acid since it increases the solubility of the ester in water.
5.
When larger runs are made, the yields increase; thus
2000 g. of ethyl acetate and
200 g. of sodium give
515–568 g. of ethyl acetoacetate. From a run of this size it is possible to recover about
700 cc. of ethyl acetate. An approximately proportional recovery is obtained in smaller runs.
The yield is based on ethyl acetate and not on sodium, because it is uncertain whether one atom or two atoms of sodium react with one mole of ethyl acetate.
3. Discussion
Ethyl acetoacetate can be prepared from
ethyl acetate by the action of
sodium,
1 sodium ethoxide,
2 sodamide,
3 and
calcium.
4 When the condensation, using
sodium ethoxide, is carried out in such a manner as to remove the alcohol formed, the yield is reported to be
80 per cent of the theoretical amount.
5
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
ethyl alcohol,
alcohol (64-17-5)
calcium chloride (10043-52-4)
potassium carbonate (584-08-7)
acetic acid (64-19-7)
ethyl acetate (141-78-6)
sodium hydroxide (1310-73-2)
calcium (7440-70-2)
sodium (13966-32-0)
sodium ethoxide (141-52-6)
Ethyl acetoacetate,
Acetoacetic acid, ethyl ester (141-97-9)
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