Organic Syntheses, Coll. Vol. 6, p.797 (1988); Vol. 55, p.77 (1976).
has been identified as a carcinogen; OSHA has issued emergency standards on its use. All procedures involving benzene
should be carried out in a well-ventilated hood
, and glove protection is required.
A. Dipotassium salt of nitroacetic acid
. A 3-l., three-necked, round-bottomed flask
equipped with a sealed mechanical stirrer
, a condenser
fitted with a calcium chloride drying tube
, and a pressure-equalizing dropping funnel
is charged with a fresh solution of 224 g. of potassium hydroxide
in 112 g. of water. From the dropping funnel is added, over 30 minutes (Note 1)
, 61 g. (1.0 mole) of nitromethane
. The reaction mixture is heated to reflux for 1 hour in an oil bath
maintained at approximately 160° (Note 2)
. After cooling to room temperature, the precipitated crystalline product is filtered, washed several times with methanol
, and dried in a vacuum desiccator
under reduced pressure, yielding 71.5–80.0 g.
) of the dipotassium salt of nitroacetic acid
, m.p. 262°
The reaction mixture is cooled to −15° ± 3° and 116 g. (1.16 moles) of concentrated sulfuric acid
is added with vigorous stirring over approximately 1 hour at such a rate that the reaction temperature is maintained at −15°. The reaction mixture is allowed to warm to room temperature over a 4-hour period and stirred for another 4 hours at room temperature. The precipitate is removed by suction filtration, and the filtrate is concentrated on a rotary evaporator
at 30–40°. The residual oil is dissolved in benzene
and washed with water. The organic layer is dried over anhydrous sodium sulfate
, and the benzene
is removed by distillation. Further distillation under reduced pressure yields 30–32 g.
) of methyl nitroacetate
, b.p. 80–82° (8 mm.)
, 111–113° (25 mm.) (Note 5)
The reaction mixture heats to 60–80° during the addition of nitromethane
. The mixture may require external heating to maintain this temperature. The initial, yellowish color begins to turn red-brown and gradually deepens as ammonia
gas is liberated.
The reaction mixture should not be stirred mechanically during this period in order to avoid decomposition of the product.
This crude product is rather pure. It can and should be employed for the esterification step without further purification. Elemental analyses for C2
were as follows; calculated:
C, 13.26; H, 0.56; N, 7.73; K, 43.16%, found:
C, 13.27; H, 0.57; N, 7.80; K, 42.68%. This is a hygroscopic crystalline powder and should be used immediately after drying. There is a report2
regarding an explosion of the dry dipotassium salt prepared by another method. There is no evidence that this procedure produces the same unstable impurities.
This must be ground into a fine powder with a mortar and pestle
immediately prior to use.
The spectral properties of the product are as follows; IR (neat) cm.−1
: 1776, 1760; 1
H NMR (CDCl3
), δ (multiplicity, number of protons, assignment): 3.83 (s, 3H, OCH3
), 5.20 (s, 2H, CH2
is an improvement in that the reaction time is reduced and the yield is improved by increasing the concentration of alkali.
The acid-catalyzed esterification has been accomplished with either hydrochloric acid3
or sulfuric acid
an improvement on the Steinkopf method has been reported,7
but the procedure lacks the simplicity of the present method.
Application of sulfuric acid
as the catalyst is considered more practical for esterification because of its higher boiling point, its incompatibility with benzene
, and the stability of nitroacetic acid
in the reaction mixture, which allows omission of the final neutralization step.
This preparation is referenced from:
Copyright © 1921-, Organic Syntheses, Inc. All Rights Reserved