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232 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

dizziness, and disturbed functioning of the stomach. A blue tinge of the lips and

face - cyanosis -is one of the most characteristic symptoms. In acute poisoning,

these symptoms are very severe and heart palpitation, loss of consciousness, cramps,

and disturbance of vision may also appear. In women it may cause severe men-

strual bleeding. The urine of people suffering from nitrobenzene poisoning contains

the blood pigment. Chronic poisoning by nitrobenzene may cause anaemia and

liver damage.

PREPARATION OF NITROBENZENE

Nitrobenzene is prepared by the nitration of benzene with mixtures of nitric

and sulphuric acids of the composition ranging from:

27 to 28% of HNO 3

56 to 58% of H 2 SO 4

14 to 17% of H 2 O

By the end of the reaction the temperature rises to 70°C.

The quantity of nitrating mixture is calculated with a small excess of HNO 3

(1%), or the nitration is carried out with a volume of mixture insufficient for com-

plete nitration (e.g. 95-97.5%). In the latter case the spent acid does not contain

any nitric acid or nitrogen oxides. Nitrobenzene, together with unreacted benzene,

is separated from the spent acid. Then benzene is separated from nitrobenzene

by distillation. The yield generally amounts to 98% on a large scale, and to about

95% in the laboratory.

At present the nitration of benzene is one of the simplest processes in the organic

chemical industry. Nevertheless, the safety factor should not be neglected. The

explosion in Rummelsburg of the plant for the nitration of benzene to nitrobenzene,

described earlier (p. 152), was the result of defective operation of the nitrator.

The manufacture of nitrobenzene on an industrial scale in the Griesheim (I. G.

Farbenindustrie) plant is described below:

2300 kg of benzene is fed to the nitrator and 6500 kg of the nitrating mixture

of the composition:

HNO 3 28%

H 2 SO 4 58%

H 2 O 14%

is added gradually, with vigorous stirring.
At the beginning of acidification a temperature of 25°C should be maintained.
During the addition of the first 4000 kg of acid the temperature is allowed to rise
up to 35°C. On adding a further 2500 kg of acid the temperature rises up to 60°C.
Then the whole is mixed for an hour at 70°C. After cooling, the layer of nitro com-

pound is separated from that of the acid. The spent acid is shaken with benzene

to remove any nitrobenzene, nitric acid and nitrogen oxides that may be left. Then
the spent acid is transferred to a distillation plant, where it is subjected to concen-

tration up to 70% of H 2 SO 4. The benzene from the extraction is either recycled
to the nitration plant or is distilled off to separate it from nitrobenzene.