urbaf2

NITRO DERIVATIVES OF TOLUENE

To obtain 100 kg of nitrotoluene require

277

toluene 69 kg

mixed acid 150 kg

sodium hydroxide solution (10%) 2.2 kg

electricity 22 kWh

steam 930 kg

The washed and dried crude product should have a setting point not lower

than 15.1%.

At Griesheim a continuous method of nitrating toluene to nitrotoluenes was

also used. The nitration unit consisted of two nitrators connected by their bottom

outlets, fed with mixed acid of the same composition as in the batch process.

The temperature in the two nitrators was:

I 25°C

II 45°C

The product and spent acid overflowed into a lead-lined separating tank. The

nitration product contained l-2% of dinitrotoluene.

SEPARATION OF ISOMERS

The composition of the mononitrotoluenes prepared at Griesheim is:

62-63% ortho

33-34% para

3-4% meta

Distillation of crude nitrotoluene. The still kettle is of 60 m^3 capacity, heated
with 18.5 atm steam. The column has 40 plates, 8 m height, 2 m diameter.
55,000 1. of the crude, steam distilled and dried nitrotoluene are sucked into
the still while heating up. Distillation begins under reduced pressure (15 mm Hg
on the receiver and 120 mm Hg in the kettle) at a still temperature of 160°C. First
runnings (ca. 200 1.) have a setting point lower than -10°C and contain nitro-
benzene. As soon as the setting point reaches -10°C the second fraction (mainly
o- nitrotoluene) is collected at a still base temperature of 180°C. The bulk of this
faction has a setting point of -9.2°C.
When the contents of the still have a setting point of 40°C, the column is emp-
tied into the base and distillation is continued without the column, at the still base
temperature 185°C. This third fraction (mainly p-nitrotoluene) has a setting point
of 40°C. The residue is tar.
Further purification is carried out by crystallization.
Crystallization of p- nitrotoluene. 8000 1. of crude molten p- nitrotoluene are
charged into a tubular crystallizer, cooled to 39-40°C and this temperature is main-
tained for 24 hr. Then the whole is cooled to 18°C for 24 hr and the crystallizer is
opened. The mother liquor is collected and the crystalline contents heated slowly
to 50°C. The oil that was drawn off is collected separately and when it reaches