276 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVESare separated individually, as all three are raw materials for the manufacture of the
corresponding toluidines and tolidines, which are valuable dyestuffs intermediates.
Recently, as the disposal of large volumes of toxic waste waters from the puri-
fication of TNT by sulphitation has. become a problem (p. 390), new ways are
being sought for the manufacture of TNT free from the unsymmetrical isomers.
Apart from the possibility, mentioned above, of the utilization of nitrotoluene
obtained by nitrating toluene with a mixture of acetic anhydride and nitric acid,
factories TNT are now tending to separate nitrotoluene isomers by methods similar
to those applied in the manufacture of dyestuffs intermediates.
This separation may be accomplished in two ways:
(1) By fractional distillation (under reduced pressure, if possible).
(2) By freezing. When the mixture has been cooled to about -12°C, p- nitro-
toluene crystallizes out, while the o- and m- isomers remain liquid. Further
cooling results in the crystallization of o- nitrotoluene, while the m- isomer
remains liquid, forming an eutectic with the o- isomer.
The Griesheim (I. G. Farbenindustrie) method, described below, may be
cited as an example of an industrial method of preparing and separating
nitrotoluenes.
3000 1. of toluene are run into a nitrator of 12 m^3 capacity. Mixed acid of com-
position :HNO 3 28-32%
H 2 SO 4 52-56%
H 2 O 20-12%is added in over a period of 8 hr at a temperature of 25°C. The amount of acid
is 99% of the theoretical, calculated on the quantity of HNO 3 required. After
adding all the mixed acid, the temperature is raised to 35-40°C and the nitrator
contents are stirred for 2 hr. A sample taken from the nitrator should have a den-
sity of 1.155-1.160 g/cm3
.
The stirrer is then stopped and the contents allowed to settle for 2 hr. The waste
acid (the lower layer) containing less than 0.2% HNO 3 (sp. gr. = 1.60-1.61) is
transferred to a storage vessel.
The oil is run into a washing tank where it is mixed with 100 1. of a 10%
NaOH solution. The aqueous alkaline solution becomes dark red owing to the
presence of sodium salts of mono- and di-nitrocresols.
The aqueous layer is separated and the oil washed with water until alkali free
when tested with phenolphthalein. The oil is steamed to remove un-nitrated
toluene and aliphatic compounds. Distillation is continued until the oil coming
over sinks in water. The distillate is collected and fractionated once or twice a year.
It contains ca. 20% of nitrotoluenes.
The steamed oil is dried in a drier of 25 m^3 capacity under reduced pressure
(40 mm Hg) until a sample dissolves completely in an equal volume of 95%sulphuric acid.