Organic Syntheses, Coll. Vol. 4, p.467 (1963); Vol. 31, p.59 (1951).
In a 1-l. round-bottomed flask
fitted with a thermometer
and a mechanical stirrer
are placed 130 ml. of saturated aqueous magnesium sulfate
solution, 500 ml. of light petroleum ether (Note 1)
, 50 g. (0.42 mole) of ethyl lactate (Note 2)
, and 20 g. (0.13 mole) of sodium dihydrogen phosphate dihydrate
. The stirrer is started (Note 3)
, the temperature is brought to 15° by means of an ice-water bath
, and 55 g. (0.35 mole) of powdered potassium permanganate
is added during 25–30 minutes. Stirring is continued until the oxidation is complete (Note 4)
, the temperature being kept near 15° throughout the process. The petroleum ether
solution is decanted and the sludge stirred with three 50-ml. portions of light petroleum ether
. The combined petroleum ether
extracts are evaporated on a steam bath
under a short fractionating column (Note 5)
. The residual oil is shaken thoroughly with two 10-ml. portions of a saturated aqueous calcium chloride
solution (Note 6)
and then distilled under reduced pressure. Almost the whole product boils at 56–57°/20 mm.
The yield is 25–27 g.
) of nearly pure ethyl pyruvate
1.4053. This product compares favorably with material prepared by esterification of pyruvic acid (Note 7)
. Further purification may be effected through the sodium bisulfite
compound (Note 8)
, b.p. 40–60°
, was washed with concentrated sulfuric acid
before use. The checkers used the hexane
fraction of petroleum.
The ethyl lactate
should be of good quality, as its impurities tend to appear in the final product. The submitter used a good commercial grade supplied by British Industrial Solvents, Ltd. Its specification included an ester content of not less than 99% (calculated as ethyl lactate
The commercial 99% ethyl lactate
available to the checkers did not give satisfactory results. It was purified by distillation through a fractionating column 8 by in., packed with glass beads
. The portion having the following properties was used: b.p. 154–155°
The thick lower layer is stirred continuously and not too fast. Vigorous agitation of the upper layer is not advisable. A short Hershberg wire stirrer
The oxidation requires about 2.5 hours. Unreduced permanganate is easily detected by spotting on filter paper
. If a cake of manganese dioxide
is formed beyond the compass of the stirrer, it should be pushed down. It is rarely necessary to do this more than once.
The distillate of petroleum ether
, which contains ethanol
and some ethyl pyruvate
, can be recovered for another run by shaking with a little concentrated sulfuric acid
This treatment removes unoxidized ethyl lactate
. Each shaking should be continued for 5 minutes. It is convenient to separate the layers by centrifuging. Droplets of calcium chloride
solution should not be present in the oil when it is to be distilled, or some polymerization will occur.
No satisfactory criterion of purity for ethyl pyruvate
is available in the literature. The submitter used a method of assay which was devised2
for the estimation of aldehydes. One hundred and sixteen milligrams of the ester is weighed in a 100-ml. conical flask
, dissolved in 5 ml. of water, and treated with 0.3 ml. of saturated sodium bisulfite
solution. After 1–2 minutes, a little starch solution is added, the mixture is chilled, and 0.1N iodine
solution is run in as rapidly as possible until the blue color is stable for a few seconds (about 12 ml. is required). Six milliliters of saturated sodium bicarbonate
solution is added, and titration with iodine
solution is carried out in the ordinary way. The end point is stable for 1 minute or more. The theoretical volume of 0.1N iodine
required for pure ethyl pyruvate
in the second stage is 20 ml. Thus if n
ml. is required the estimated purity is 5n
%. The results are perfectly consistent but may be slightly lower than the true values owing to dissociation of the bisulfite complex. The results from four different samples are as tabulated.
Method of Preparation
Estimated Ethyl Pyruvate Content, %
(1) Oxidation of ethyl lactate
(2) Esterification of once-distilled pyruvic acid
(3) Sample (2) twice redistilled; fraction b.p. 147–148° taken
(4) Sample (1) purified through bisulfite complex (Note 8)
The bisulfite compound is best made in small batches. The ester (2.2 ml.) in a large test tube
is underlaid with 3.6 ml. of saturated sodium bisulfite
solution. The tube is chilled in a freezing mixture, and the layers are shaken together. Crystallization occurs rapidly, especially if seed crystals are present. After 3 minutes, 10 ml. of ethanol
is added and the crystalline product is washed on a filter with ethanol
. The yield is 3.0 g. Sixteen grams of the bisulfite complex
is mixed with 32 ml. of saturated magnesium sulfate
solution, and 5 ml. of 40% formaldehyde
is added. After shaking, the oil is separated and the aqueous layer extracted with a little ether
, which is added to the oil. After drying with magnesium sulfate
the product is distilled at low pressure and affords 5.5 g.
of ethyl pyruvate
, b.p. 56°/20 mm.
On redistillation, the purified ester boils at 147.5°/ 750 mm.
1.4052, f.p. around −50°.
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