Submitted by S. M. McElvain and K. H. Weber.
Checked by R. L. Shriner and C. H. Tilford.
1. Procedure
A
2-l. three-necked flask is mounted on a
steam bath and fitted with a
reflux condenser, a
separatory funnel, and an
efficient sealed stirrer. In the flask is placed
600 ml. of absolute ethanol, and to this is added gradually
46 g. (2 gram atoms) of clean sodium cut into small pieces. The
sodium ethoxide solution is stirred and cooled to room temperature, after which
267 g. (260 ml., 2.05 moles) of ethyl acetoacetate (Note
1) is added slowly through the separatory funnel. The reflux condenser is then replaced by a short still head, and the
ethanol is removed by distillation at approximately room temperature and under the pressure of a
water pump. When approximately half the
ethanol has been removed, sufficient sodium enolate precipitates so that stirring has to be discontinued. When the residue appears dry (after about 2 hours) the last traces of
ethanol are removed by heating for an hour on the steam bath under a pressure of 2 mm. The flask is allowed to cool to room temperature under reduced pressure.
To the cooled residue of sodium enolate is added
600 g. (570 ml., 4 moles) of ethyl benzoate. The steam bath is replaced by an
oil bath, and the temperature of the bath is raised to 140–150° and maintained there for 6 hours. Then, over a period of another hour, the temperature of the bath is gradually raised to 180° (Note
2). The distillate that is collected during this period of heating amounts to 200–210 g. and consists chiefly of
ethyl acetate and
ethanol.
The reaction mixture is cooled, 250 ml. of water is added, and the mixture is made acid to litmus by addition of a cooled solution of
100 g. of concentrated sulfuric acid in 200 ml. of water. Chipped ice is added if necessary to keep the mixture cool. The upper ester layer is separated, and the aqueous layer is extracted with
200 ml. of ether. The combined
ether and ester layers are shaken with
350 ml. of a saturated sodium bicarbonate solution until no more
carbon dioxide is evolved, and then the organic layer is washed with 200 ml. of water. The water layer is combined with the
sodium bicarbonate solution and extracted with
400 ml. of ether. The combined
ether and ester layers are dried over
sodium sulfate. The
ether is removed by distillation on the steam bath, and the excess
ethyl benzoate and acetoacetic ester (Note
3) are then removed by distillation under reduced pressure through a
15-cm. fractionating column. Finally, the
ethyl benzoylactetate is distilled (Note
3) at
101–106° /1 mm. (
130–135° /3 mm.). The yield of ester boiling over a 5° range is
190–210 g. (
50–55% based on the
ethyl acetoacetate).
2. Notes
1. Commercial
ethyl acetoacetate was distilled, and the fraction boiling at 68–69° /11 mm. was used.
3. A mixture of
ethyl acetoacetate and
ethyl benzoate (100–150 g.) was collected at 75–90° /12 mm., after which
250–300 g. of pure ethyl benzoate, b.p. 90–93° /12 mm., was recovered. These products were removed through a 15-cm. fractionating column. The remaining
ethyl benzoylacetate was distilled through a short still head without a fractionating column.
3. Discussion
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