Org. Synth. 1926, 6, 40
DOI: 10.15227/orgsyn.006.0040
ETHYL ACETOPYRUVATE
[Valeric acid, α,γ-dioxo-, ethyl ester]
Submitted by C. S. Marvel and E. E. Dreger.
Checked by Frank C. Whitmore and Gladys E. Woodward.
1. Procedure
In a 5-l. round-bottomed flask fitted with a reflux condenser, a mechanical stirrer (Note 1) and a 1-l. separatory funnel, is placed 2800 cc. of absolute ethyl alcohol (Note 2), and to this is added 125 g. (5.4 atoms) of sodium over a period of one to two hours. The stirrer is started and the mixture allowed to cool to room temperature (Note 3), and a mixture of 730 g. (673 cc., 5 moles) of ethyl oxalate (Note 4) and 290 g. (366 cc., 5 moles) of acetone (Note 5) is added slowly over a period of two to three hours. At first a white precipitate forms; this is followed by a yellow precipitate that darkens as the reaction proceeds and later turns yellow again. The temperature rises to about 40°. Toward the end the mixture becomes so thick that stirring is difficult. Stirring is continued for one hour after the addition of the oxalate and acetone mixture. The yellow sodium salt is filtered by suction on two 20-cm. Büchner funnels (Note 6). The reaction flask is rinsed with 200 cc. of absolute ethyl alcohol, which is then used to wash the salt. The filtrate is turbid as a rule, but there is not enough sodium salt in suspension or solution to warrant recovery.
When the sodium salt has been sucked dry, it is returned to the
5-l. flask and treated with 1.5 l. of water and 1 kg. of cracked ice. The stirrer is started and there is added rapidly a cold
sulfuric acid solution made by adding enough ice to
200 cc. of concentrated sulfuric acid (sp. gr. 1.84)
(Note 7) so that some of the ice is not melted. The stirring is continued for five or ten minutes or until the yellow lumps of the sodium salt disappear. The mixture is then extracted with three
600-cc. portions of benzene (Note 8). The
benzene is distilled
(Note 9) from the extracts on a water bath and the residue is transferred to a special
2-l. Claisen flask (p. 130) and distilled under diminished pressure. The product boils at
130–132°/37 mm. or
117–119°/29 mm. A small high-boiling fraction is redistilled to yield
20–30 g. more of the
ethyl acetopyruvate. The total yield is
480–520 g. (
61–66 per cent of the theoretical amount)
(Note 10).
2. Notes
1.
The stirrer used is a
bent glass rod which nearly scrapes the sides of the flask. A simple
paddle stirrer is not efficient enough to stir the semi-solid mass.
2.
The quality of the absolute
alcohol (p. 249) influences the yields decidedly. The amount of alcohol indicated is the smallest which can be used effectively.
3.
No better yields were obtained at lower temperatures.
4.
The
ethyl oxalate used
(p. 261) was dried over
calcium chloride for a week.
5.
The
acetone used was commercial
acetone dried over
calcium chloride for a week and then distilled. Some
acetone is lost in this operation as it combines chemically with the
calcium chloride.
1 See, Org. Syn.
20, 7.
6.
The filtration is likely to be slow and may take as much as two or three hours. When a
40-cm. Büchner funnel was used, it was complete in less than one hour.
7.
This is sufficient acid to turn Congo red paper distinctly blue. If less acid is used, a troublesome emulsion is likely to form. If such an emulsion forms it can be broken by pouring into it a small amount of
sulfuric acid cooled by the addition of ice.
8.
If less than
600-cc. portions of benzene are used, the danger of emulsion formation is greater.
9.
About
1 l. of benzene is recovered.
10.
Care should be exercised in storing
ethyl acetopyruvate because spontaneous decomposition, accompanied by gas evolution, may shatter the container.
3. Discussion
Ethyl acetopyruvate can be prepared by the condensation of
ethyl oxalate and
acetone in the presence of
sodium ethoxide.
2 The procedure described is based on that of Claisen and Stylos.
2 It is reported that the condensation of
ethyl oxalate and
acetone by means of
sodium methoxide furnishes
methyl acetopyruvate in excellent yields and that the reaction requires less care than when the ethoxide is used.
3
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)
sulfuric acid (7664-93-9)
Benzene (71-43-2)
acetone (67-64-1)
sodium methoxide (124-41-4)
sodium (13966-32-0)
sodium ethoxide (141-52-6)
Ethyl acetopyruvate,
Valeric acid, α,γ-dioxo-, ethyl ester (615-79-2)
Ethyl oxalate
methyl acetopyruvate (20577-61-1)
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