Organic Syntheses, CV 2, 583
Submitted by G. H. Coleman and David Craig.
Checked by Henry Gilman and J. B. Dickey.
1. Procedure
The apparatus shown in
.htmFig. 18 is set up in a
hood. The
narrow reaction bottle A, of about 500-cc. capacity and having a wide mouth, is provided with an
efficient mercury-sealed mechanical stirrer, an
inlet tube B for admitting the mixture of gases, and an
outlet tube connected with the
wash bottle E. Into A, contained in a
water bath at 20°, is placed
200 g. (2.17 moles) of dry toluene; then
30 g. (0.3 mole CuCl) of cuprous chloride (Note
1) and
267 g. (2 moles) of finely powdered anhydrous aluminum chloride are added rapidly with active stirring.
Fig. 18
A mixture of
hydrogen chloride and
carbon monoxide (Note
2) is led to the bottom of the reaction bottle through tube B at such rates that the
carbon monoxide is admitted uniformly during seven hours and the
hydrogen chloride at about one-half this rate. The rates of flow of the two gases may be compared by the bubbling in wash bottles C and D. The extent of absorption can be estimated from the bubbling of the effluent gases in wash bottle E. The
carbon monoxide is absorbed almost quantitatively at the beginning, and as the mixture thickens the absorption becomes less complete.
The mixture is hydrolyzed by adding it (Note
3) slowly and with shaking to 1.5 kg. of cracked ice in a
3-l. flask. The resulting mixture is then steam-distilled until all the aldehyde and unchanged
toluene are driven over.
Fifty cubic centimeters of ether is added to the distillate, the two layers are separated, and the aqueous layer is washed with
150 cc. of ether which is then added to the first non-aqueous layer (Note
4). After drying with
calcium chloride, the aldehyde is obtained by distilling from a
500-cc. flask provided with a short fractionating column (Note
5). The yield of
p-tolualdehyde distilling at
201–205° is
121–132 g. (
46–51 per cent of the theoretical amount based on the
toluene). Redistillation involves but a slight loss and gives an almost colorless product which distils at
203–205° (Note
6).
2. Notes
2. The
carbon monoxide may be forced by water from a
75-l. container, after which it is dried by bubbling through two
wash bottles containing concentrated sulfuric acid.
In place of this large container for
carbon monoxide it is possible to generate the gas more conveniently by adding
170 g. (141 cc., 3.69 moles) of pure formic acid (sp. gr. 1.2) to
250 g. (135.8 cc.) of concentrated sulfuric acid contained in a
1-l. distilling flask heated on an
oil bath to 70–80°. The side arm of the flask is connected to the sulfuric acid wash bottles. In order to ensure a smooth and constant flow of
carbon monoxide, the
formic acid is placed in a
dropping funnel which extends through a
two-holed rubber stopper in the neck of the distilling flask. The other hole of this stopper is connected by rubber tubing to a
one-holed stopper in the dropping funnel. No frothing was evident under these conditions, but should frothing occur it is recommended that a small quantity of paraffin be added to the
sulfuric acid in the generating flask.
3. The mixture frequently is too thick to be poured, and a
spatula must be used to remove it.
4. The extraction of the aldehyde from the unchanged
toluene with
sodium bisulfite at this point in the preparation does not appreciably increase the purity of the product.
5. It is necessary to use a
water-condenser until the temperature reaches 150°, after which an
air-condenser is used.
3. Discussion
The method described is that of Gattermann and Koch.
1 p-Tolualdehyde has also been prepared from
toluene,
hydrogen cyanide,
hydrogen chloride, and
aluminum chloride;
2 from
toluene,
nickel carbonyl, and
aluminum chloride;
3 from
p-tolunitrile by reduction with
stannous chloride followed by hydrolysis of the aldimine;
4 from
p-xylene by oxidation, particularly with
chromyl chloride;
5 and from
p-tolylmagnesium bromide with
formaldehyde phenylhydrazone,
6 ethyl orthoformate,
methylformanilide,
ethoxymethyleneaniline, or
carbon disulfide. The syntheses involving the Grignard reagent, except the first mentioned, have been examined and evaluated by Smith and Bayliss
7 and Smith and Nichols:
7 the use of
ethoxymethyleneaniline or of
ethyl orthoformate is recommended.
This preparation is referenced from:
Copyright © 1921-2002, Organic Syntheses, Inc. All Rights Reserved