A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1922, 2, 59
DOI: 10.15227/orgsyn.002.0059
[α-Toluic acid, p-nitro-]
Submitted by G. Ross Robertson
Checked by Roger Adams and H. O. Calvery.
1. Procedure
In a 1-l. round-bottomed flask is placed 100 g. (0.62 mole) of p-nitrobenzyl cyanide (p. 396). A solution of 300 cc. (5.4 moles) of concentrated sulfuric acid (sp. gr. 1.84) in 280 cc. of water is prepared, and two-thirds of this solution is poured onto the p-nitrobenzyl cyanide. The mixture is shaken well, until the solid is all moistened with the acid. Any solid material adhering to the walls of the vessel is now washed down into the liquid with the remainder of the acid; the flask is attached to a reflux condenser, then set, without shaking, over a 10-cm. hole in a large sheet of asbestos board which rests on a tripod, and heated until the mixture boils (Note 1). The boiling is continued for fifteen minutes (Note 2).
The reaction mixture, which becomes rather dark, is diluted with an equal volume of cold water and cooled to 0° or below. The solution is filtered; the precipitate is washed several times with ice water and then dissolved in 1600 cc. of boiling water (Note 3). This solution is filtered as rapidly as possible through a large folded filter, preferably with a steam funnel (Note 4). In spite of all precautions, however, some solid usually separates on the filter. This must be redissolved in a minimum quantity of boiling water, and this solution then filtered into the main solution. The p-nitrophenylacetic acid separates in long, pale yellow needles, which melt at 151–152°. The yield is 103–106 g. (92–95 per cent of the theoretical amount).
2. Notes
1. If the flask is not protected with an asbestos board or the equivalent, decomposition occurs where the substance is superheated on the side walls of the flask. If crystals of the cyanide are allowed to remain on the upper walls of the flask, they are not easily washed down and so are not hydrolyzed.
2. In making experiments with 500 g. of p-nitrobenzyl cyanide, it was found that the time for hydrolysis was about the same as when smaller amounts were used.
3. If a good grade of cyanide is used, it is not necessary to add animal charcoal in order to obtain the acid in a pure state. With technical p-nitrobenzyl cyanide, a few grams of animal charcoal are added in dissolving the precipitate.
4. The solubility curve of p-nitrophenylacetic acid is very steep at temperatures near 100°, so that the filtering of the boiling solution should be rapid.
3. Discussion
p-Nitrophenylacetic acid can be prepared by the nitration of phenylacetic acid1 and by the hydrolysis of its nitrile with hydrochloric acid.2

References and Notes
  1. Maxwell, Ber. 12, 1765 (1879); Borsche, Ber. 42, 3596 (1909).
  2. Gabriel, Ber. 15, 834 (1882).

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

sulfuric acid (7664-93-9)

hydrochloric acid (7647-01-0)

Phenylacetic acid (103-82-2)

p-Nitrophenylacetic acid (104-03-0)

p-Nitrobenzyl cyanide (555-21-5)

α-Toluic acid, p-nitro-