urbaf2

NITRO DERIVATIVES OF HALOGENOBENZENES 459

is added to the solution at 40-55°C, while stirring and cooling. The whole is heated

to 70°C and stirred at this temperature for 2 hr. When nitration has been completed
the stirrer is stopped and the mixture is allowed to remain at rest. After it has sepa-

rated into two layers, the lower one - spent acid containing 70% of H 2 SO 4 - is

transferred to a tank of 13 m

3
capacity lined with acid resistant bricks, where it is
agitated with chlorobenzene. The chlorobenzene, now containing chloronitroben-

zne extracted from the spent acid, is used for nitration, while the acid freed
from the nitro compound is concentrated.

Dinitration. 5100 kg of a nitrating mixture of the composition:

HNO 3 35%

H 2 SO 4 65%

is run into the nitrator containing the chloronitrobenzene, a temperature of 50-55°C

being maintained by cooling.

The whole is heated to 70°C and stirred for 2 hr at 70-80°C. Nitration is com-

plete if a sample of the product has a melting point of 47.6°C, and, when steam

distilled after being brought to alkalinity, the distillate does not smell of o- nitro-

phenol. After nitration has been completed, the whole is cooled to 50°C diluted

at this temperature with 390 kg of water and allowed to remain at rest for separation.

The lower spent acid layer, containing 78% of H 2 SO 4 is used for mononitration.

Chlorodinitrobenzene forming the upper layer is washed with warm water.

then with a warm dilute solution of sodium carbonate and again with warm water,

until entirely free from acid. Then it is dried by heating under reduced pressure

in a 20 m^3 tank.

From 100 parts of chlorobenzene 175 parts of chlorodinitrobenzene with a melt-

ing point of 47.6°C is obtained, which corresponds to 97.5% of the theoretical

yield.

TRINITRO DERIVATIVES OF CHLOROBENZENE

Of the trimtro derivatives of chlorobenzene, l-chloro-2,4,6-nitrobenzene

(m. p. 81.5-83°C), known also as picryl chloride, is the most important. Next

in importance is 1-chloro-2,4,5-trinitrobenzene (m. p. 116°C):

picryl chloride

l-Chloro-2,4,6-trinitrobenzene (picryl chloride) was obtained by Pisani in 1854,

in the reaction of phosphorus pentachloride with picric acid. Similarly Ullmann [25]

prepared picryl chloride when treating picric acid with toluene-p-sulphonchloride.