Organic Syntheses, Coll. Vol. 3, p.644 (1955); Vol. 29, p.72 (1949).
In a 3-l. three-necked flask
provided with a dropping funnel
, a thermometer
, and an efficient mechanical stirrer
is placed 1.25 l. of technical concentrated sulfuric acid
(sp. gr. 1.84). The acid is stirred during the fairly rapid addition of 167 ml. (250 g., 4 moles) of technical fuming nitric acid
(sp. gr. 1.49–1.50), with sufficient cooling by an ice bath
so that the temperature of the mixed acids does not exceed 10°. The mixture is maintained at 5–10° while 213 g. (2 moles) of U.S.P. benzaldehyde (Note 1)
is added with good stirring over a period of 2–3 hours. At the end of the addition the ice bath is removed and the mixture is allowed to stand overnight at room temperature.
The mixture is poured carefully onto about 3.25 kg. of cracked ice in a 2-gal. crock (Note 2)
with manual stirring. The yellow precipitate is collected on a large Büchner funnel
, washed with cold water, and pressed as dry as possible (Note 3)
. Further removal of water is accomplished by dissolving the moist product in about 100 ml. of warm benzene
and separating the water layer in a separatory funnel
. The benzene
solution is filtered (Note 4)
into a 1-l. distilling flask
and concentrated on a steam bath
. Distillation is discontinued when benzene
no longer comes over or when nitrous fumes (from incompletely removed nitric acid
) appear. The residual m-nitrobenzaldehyde
is sufficiently pure for use in the next step (Note 5)
B. m-Nitrobenzaldehyde dimethylacetal.
The above crude product is dissolved in 750 ml. of technical anhydrous methanol
, 1 ml. of concentrated hydrochloric acid
is added if necessary (Note 6)
, and the solution is allowed to stand at room temperature for 5 days (Note 7)
. A solution of sodium methoxide in methanol
is added until the solution is just alkaline to moistened litmus paper. The methanol
is removed by distillation on a steam bath; the residue is cooled to room temperature and treated with cool water to dissolve the inorganic salts. The aqueous solution is extracted with two 50-ml. portions of ether
, and the extracts are added to the crude acetal
. The solution is subjected to a preliminary drying over anhydrous magnesium sulfate (or sodium sulfate)
, filtered, and then dried for at least 12 hours over anhydrous sodium carbonate
. After the ether
has been removed by distillation on a steam bath the residue is distilled under reduced pressure from a 500-ml. Claisen flask
. The yield of the light-yellow liquid acetal
, boiling at 141–143°/8 mm. (Note 8)
, is 300–335 g.
) (Note 9)
may contain some benzoic acid
. When taken from a previously unopened bottle, U.S.P. benzaldehyde
usually is quite satisfactory. If there is any doubt concerning its purity, the aldehyde may be washed with dilute sodium carbonate
solution, dried over anhydrous sodium carbonate
, and distilled under diminished pressure just before use.
Two 4-l. beakers
may be used.
A small amount of an oily liquid passes through the filter; this material is a mixture of the ortho
isomers. If a very pure product is desired, this oil may be discarded, although some of the meta
isomer will be lost. It is usually satisfactory to combine it with the solid material, the m-nitro acetal
being obtained in a state of purity sufficient for most purposes in the final distillation.
A small amount of a solid by-product is removed.
If pure m-nitrobenzaldehyde
is desired, the benzene
solution is diluted with additional benzene
and is washed well with aqueous sodium bicarbonate
solution until the washings are alkaline. (Warning! It has been reported
] that incomplete washing of the product in solution may result in an explosion during the distillation; all remaining acids must be removed before distillation is attempted
.) The solution is dried (with anhydrous sodium
or magnesium sulfate
), and the solvent is removed. The aldehyde is distilled under reduced pressure from a Claisen flask connected to an air-cooled condenser. The yield of product boiling at 119–123°/4 mm.
is 226–254 g.
). The product readily crystallizes in the receiver.
When nitrous fumes are observed, there usually is enough acid present to catalyze the acetal
The yield is not increased by extending the reaction period beyond 5 days.
boils at 116–119°/1 mm.
, 122–126°/2 mm.
, 130–132°/3 mm.
The boiling range depends somewhat upon the rate of distillation.
The submitters obtained yields in the upper part of this range from runs twice the size described. They have stored samples of the product for as long as 4 years without deterioration.
The only satisfactory method for the preparation of m-nitrobenzaldehyde
is the direct nitration of benzaldehyde
with a mixture of nitric and sulfuric acids. The procedure described is essentially that of Baker and Moffitt.1
This preparation is referenced from:
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