Organic Syntheses, Coll. Vol. 4, p.31 (1963); Vol. 31, p.6 (1951).
To 600 ml. of distilled water in a 1-l. beaker
are added 30 g. (0.125 mole) of crystalline sodium sulfide nonahydrate (Note 1)
, 15 g. (0.47 g. atom) of flowers of sulfur
, and 27 g. (0.67 mole) of sodium hydroxide pellets
. The mixture is heated on a steam bath
for 15–20 minutes with occasional stirring and then poured into a 2-l. round-bottomed flask
containing a hot solution of 50 g. (0.36 mole) of p-nitrotoluene (Note 2)
in 300 ml. of 95% ethanol
. A reflux condenser
is attached, and the mixture is heated under reflux for 3 hours. The resulting clear but deep red solution is rapidly steam-distilled until about 1.5–2 l. of condensate has been collected (Note 3)
. The distillate should be clear when the distillation is stopped. The residue in the 2-l. flask should have a volume of 500–600 ml.; if less, it should be diluted to this volume with boiling water. The solution is rapidly chilled in an ice bath with occasional vigorous shaking and stirring to induce crystallization. After 2 hours in the ice bath the golden yellow crystals of p-aminobenzaldehyde
are collected on a Büchner funnel
and washed with 500 ml. of ice water to remove sodium hydroxide (Note 4)
. The product is immediately placed in a vacuum desiccator
over solid potassium hydroxide pellets
for 24 hours. The yield of p-aminobenzaldehyde
, m.p. 68–70°
, amounts to 18–22 g.
). The product contains some impurities but is pure enough for most purposes (Note 5)
. It should be stored in a sealed bottle (Note 6)
It has been reported2
that a large amount of a dark oily tar may be present at this stage. Presumably it consists of Schiff's base polymers which have formed during the time necessary for reflux and steam distillation. The clear solution may be decanted from the oil, and the expected orange-yellow crystals of p-aminobenzaldehyde
are obtained on cooling the solution.
The oily tar may be dissolved in boiling acetic anhydride
, and upon dilution of the reaction mixture with water and partial concentration, crude p-acetamidobenzaldehyde
separates. The latter may be purified by dissolving it in hot sodium bisulfite
solution and fractionally precipitating the aldehyde by the addition of sodium hydroxide
solution. From 12.3 g. of intractable tars there were obtained a first fraction which consisted of a dark sludge which was discarded, a second fraction which weighed 5.2 g., m.p. 150°, and a third which weighed 1.9 g., m.p. 147°. The melting point of p-acetamidobenzaldehyde
It is sometimes necessary to suspend the precipitate in about 200 ml. of ice water, stir it vigorously, and filter again to remove all traces of alkali.
The chief impurities are the polymeric condensation products of p-aminobenzaldehyde
with itself. No satisfactory method for recrystallization has been found. If the melting point is high and a pure product is desired, it is best to extract with boiling water until the filtrate is clear, and extract the monomer from the water with ether
. This procedure gives recoveries of 25–30%.
Readily purified aldehyde derivatives may be prepared in good yields from the crude polymer mixture. The oxime melts at 124°, the azine at 245°, and the phenylhydrazone at 175°.4
If these derivatives are hydrolyzed, the same crude p-aminobenzaldehyde
of broad melting range results.
Care must be taken to exclude all traces of acid fumes from p-aminobenzaldehyde
, since they catalyze its self-condensation.
This preparation is referenced from:
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