Submitted by G. M. Bennett and E. V. Bell.
Checked by J. B. Conant and R. E. Schultz.
1. Procedure
A solution of
300 g. (2.5 moles) of technical dimethylaniline in
1050 cc. of concentrated hydrochloric acid is placed in a
large jar or crock and finely divided ice is added until the temperature has fallen to 5°. The contents of the jar are then stirred mechanically, and a solution of
180 g. (2.6 moles) of sodium nitrite in 300 cc. of water is slowly added from a
separating funnel, the stem of which dips beneath the surface of the liquid. The addition takes one hour, and the temperature is kept below 8° by the addition of ice if necessary. When all the nitrite has been added the mixture is allowed to stand one hour and then filtered. The solid
p-nitrosodimethylaniline hydrochloride is washed with
400 cc. of 1:1 hydrochloric acid and then with
100 cc. of alcohol. After drying in air, it weighs
370–410 g. (
80–89 per cent of the theoretical amount) (Note
1).
In a
3-l. flask a mixture of
330 g. (1.8 moles) of air-dried p-nitrosodimethylaniline hydrochloride (Note
2) with
100 g. of anhydrous sodium carbonate and
1.5 l. of 95 per cent alcohol is heated on the
steam bath for thirty minutes and filtered to remove
sodium chloride and unchanged carbonate. The filtrate is placed with
300 g. (1.6 moles) of 2,4-dinitrotoluene (m.p.
70°) in a
5-l. flask provided with a
mechanical stirrer and a
reflux condenser and heated on the steam bath with stirring for five hours. When the contents of the flask are cold, the condensation product is collected on a
Büchner funnel and well drained by means of a
suction pump and a piece of "
rubber dam" fastened over the top of the funnel. The rubber is drawn down onto the solid by the suction, thus forcing the liquid out. The dark green solid is washed by transferring it to a
large beaker, stirring it with
1 l. of 95 per cent alcohol on the steam bath for half an hour, cooling, and filtering again, using the rubber dam. The
dinitrobenzylidene-p-aminodimethylaniline is placed while still damp in a
large round-bottomed flask containing
500 cc. of a mixture of equal volumes of concentrated hydrochloric acid and water, and steam is blown in by a tube reaching to the lowest part of the vessel. Vigorous injection of steam is continued for fifteen minutes after the liquid has reached a temperature of 105° (Note
3).
When cold the aqueous layer is decanted (or filtered) from the solidified product, and the process of steam-agitation with acid is repeated, another
500 cc. of dilute acid being added (Note
4). Finally the solid is filtered, washed with water, and dried
in vacuo. The crude
dinitrobenzaldehyde so obtained weighs
170–210 g. and melts at
40–50°. It is purified by heating in two lots each with
8 l. of naphtha (b.p.
90–110°) in a large flask on the steam bath with mechanical stirring for three hours, decanting the solution (temperature of liquid 80°) and allowing the aldehyde to crystallize. The purified
dinitrobenzaldehyde, air-dried, weighs
79–104 g. (
24–32 per cent of the theoretical amount) and melts at
69–71° (Note
5). From the mother liquors impure material may be recovered by evaporation or by distillation in steam, from which by a similar process of crystallization a further
20 g. of aldehyde of m.p.
66° can be separated.
2. Notes
1. It is reported that
p-nitrosodiethylaniline hydrochloride can be prepared by a similar procedure and that the free base can be obtained from the hydrochloride in the following way: The reaction mixture containing the
p-nitrosodiethylaniline hydrochloride prepared from
50 g. of once-distilled diethylaniline is stirred and kept at 5° while
580 cc. of 2 N sodium carbonate solution is added dropwise. The addition requires about two hours, after which the color of the reaction mixture changes to dark green and a dark green solid separates. Stirring is continued for ten minutes, then the precipitate is allowed to settle for five minutes and is filtered with suction. The precipitate is washed with three 25-cc. portions of distilled water, added dropwise by means of a
pipet, then with three
20-cc. portions of a 1:1 alcohol-ether mixture, also added dropwise. The
p-nitrosodiethylaniline is dried in a
desiccator over
calcium chloride. The material weighs
57 g. (
95 per cent of the theoretical amount). If a very pure sample is desired, the nitrosoamine should be crystallized from
petroleum ether. (M. Q. Doja and A. Mokeet, private communication.)
2. Attempts to use technical
nitrosodimethylaniline in place of the freshly prepared material were not successful.
3. It is essential that the temperature reach the maximum (about 105°) and be kept at this point for sufficient time during the hydrolysis.
5.
2,4-Dinitrobenzaldehyde is a useful reagent since it forms crystalline condensation products with amines and with substances having a reactive methylene or methyl group.
1
3. Discussion
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