Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

292 ^-TOLUIC AND TBKBPHTHALIC ACIDS
and, by staking the warm residue with a solution of 4 g. of stannous
chloride in 10 c.c. of concentrated hydrochloric acid, the azotoluene
which gives the material its yellow colour is removed. 1 The liquid
is diluted with water and the toluic nitrile which soon solidifies is
collected at the pump and dried on porous plate. If the material
remains partly oily it is dissolved in ether and shaken again with
sodium hydroxide solution in order to remove stannous chloride.
The ethereal solution is then dried and the nitrile is distilled. Boiling
point 218°. Melting point 38°. Yield 12-14 g.
Benzonitrile.—In the same apparatus benzonitrile can be prepared
in a corresponding yield from the diazonium chloride solution
obtained from 18-6 g. of aniline. Liquid boiling at 186°.
^-Toluic Acid.—If the hydrolysis of a nitrile to an acid has not
already been carried out (benzyl cyanide ->phenylacetic acid, p. 140)
this process should be learned here.
In a small round-bottomed flask mix 20 c.c. of concentrated
sulphuric acid with 10 c.c. of water and add 5-5 g. of toluic nitrile
gradually in small portions. Then heat the mixture to boiling under
reflux condenser for about one hour on the sand bath or on wire
gauze. After cooling, dilute with water, collect the crystalline acid
at the pump, remove any amide which may be present by dissolving
the crude material in dilute alkali solution and filtering, then
precipitate the toluic acid from the filtrate with hydrochloric acid.
A purer product is obtained by hydrolysis for five hours at 150° (in
the oil bath). For purification dissolve the material (not previously
dried) in the minimum quantity of boiling alcohol, add water to the
boiling solution until turbidity just fails to persist, and continue the
boiling for a few minutes longer with a little animal charcoal, but do
not add the latter while the solution is boiling. Filter and allow the
filtrate to cool. The acid which crystallises melts at 177°. Yield4 g.
The best preparative method of obtaining terephthalic acid is to
oxidise the sodium salt of y-toluic acid with permanganate at the temperature
of the water bath. In the same way toluene can be converted
into benzoic acid, and an important technical example of this reaction
is the oxidation, of o-tolylsulphonamide to saccharin.
Henle, Organ, chem. Praktikum, 3rd Ed., p. 149.