Org. Synth. 1940, 20, 26
Submitted by F. Arndt
Checked by W. W. Hartman and A. Weissberger.
A 250-ml. round-bottomed flask
is fitted with a thermometer
reaching nearly to the bottom (Note 1)
and a three- or four-bulb fractionating column
without a side arm, at the upper end of which is attached a partial condenser (Fig. 11) (Note 2)
. The side arm (A
) of the partial condenser carries a 110° thermometer
and is connected to a condenser set
for downward distillation. The inside container (B
) of the partial condenser is filled halfway with toluene
, a chip of porous plate
is added, and the top is attached to a reflux condenser
In the 250-ml. flask 100 g. (0.78 mole) of freshly vacuum-distilled ethyl acetoacetate and 0.05 g. of sodium bicarbonate (Note 3) are placed and heated so that the toluene is kept just boiling until the liquid in the flask has reached 200–210° (Note 4). The time for heating is usually 7–8 hours, during which period 27 g. of distillate boiling at 72° (mostly ethanol) is collected, and the color of the reaction mixture becomes dark brown. The dehydroacetic acid, while still hot (Note 5), is transferred to a 200-ml. distilling flask (Note 6) and distilled under reduced pressure. After a fore-run boiling up to 128° at 12 mm., consisting of ethyl acetoacetate, has been collected, the receiver is changed and dehydroacetic acid is collected up to 140°/12 mm. The yield of dehydroacetic acid melting at 104–110° is 34 g. (53%) (Note 7). A purer product, m.p. 108°, may be secured in 80% yield by recrystallization from ethanol, using 2 ml. per gram of material (Note 8).
The bulb of the thermometer must be immersed in the liquid.
This partial condenser, which is a modification of one described by Hahn,1
is very effective in reducing the time required for fractional distillation of many mixtures. It is best constructed of Pyrex. The dimensions given are approximate and may be varied to suit individual needs. The inside container is a 30 by 140 mm
. Pyrex test tube
sealed at the top to standard Pyrex tubing. It is very effective in the purification of cyclohexene [Org. Syntheses Coll. Vol. 1, 183 (1941)]
The crude hydrocarbon mixture is first put into the flask with ethanol
in the partial condenser, and the whole heated as long as a distillate is obtained. The ethanol
is then replaced by ethylene chloride
and the cyclohexene
It is essential to use sodium bicarbonate
to secure consistent results.
Above this temperature extensive decomposition sets in. The time required varies with the size of the run, being less with smaller quantities.
The residue solidifies on cooling. The dehydroacetic acid
may be filtered and washed at this stage, but the yield is lower, owing to its solubility in the reaction mixture.
An ordinary 200-ml. distilling flask with a large-diameter side arm placed well down on the neck gave the best results. There was no foaming, frothing, or spattering.
The yield falls off with larger amounts; e.g., 500 g. of ester
gave only 35%
of the calculated quantity of acid.
The acid may be isolated through the sodium salt, but the quality is poorer and the yield less.
has been prepared by the action of acetic anhydride
on acetonedicarboxylic acid
as a by-product in the pyrolysis of acetone
to give ketene
by treatment of ketene dimer with pyridine5
or sodium phenoxide
and by removal of ethanol
from acetoacetic ester
This preparation is referenced from:
Chemical Abstracts Nomenclature (Collective Index Number);
acetic anhydride (108-24-7)
sodium bicarbonate (144-55-8)
ethylene chloride (107-06-2)
Ethyl acetoacetate (141-97-9)
Dehydroacetic acid (520-45-6)
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