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458 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

Fraction II is recrystallized. From fraction III o- chloronitrobenzene is isolated

by crystallization, effected by slow cooling to 15-18°C for about 80 hr.

The resultant crystals are not washed with methyl alcohol. The product melts

at about 32°C. The crystallization liquor is added to that from the first crystalli-

zation.

At the Griesheim Works the isomers are separated in a similar way but using

chlorobenzene for washing instead of methyl alcohol.

NITRATION OF p- CHLORONITROBENZENE TO

l-CHLORO-2,4-DINITROBENZENE

According to the Griesheim method of nitration of p- chloronitrobenzene to

l-chloro-2,4-dinitrobenzene, 4500 kg of molten p- chloronitrobenzene (m. p. 82.4°C)

is introduced into a nitrator, followed by 5700 kg of a nitrating mixture,

HNO 3 35%

H 2 SO 4 65%

with simultaneous stirring and cooling.

The cast iron nitrator of 8 m^3 capacity is equipped with a jacket and a lead coil.

Nitration starts at 95°C the temperature then being lowered to 45-55°C. After

all the acid has been added the mixture is stirred for 2 hr at 65°C. Nitration is con-

sidered to be complete when a sample of the dry product solidifies at 49.6°C.

The mixture in the nitrator is then cooled to 55-60°C diluted. with 1000 kg of

water, stirred and allowed to settle. Then the lower spent acid layer is drained off

and mixed with chlorobenzene to recover nitrogen oxides and nitro compounds

present in the acid. The chlorobenzene is then nitrated to chloronitrobenzene (as

described above), while the spent acid goes to the concentration plant to obtain

concentrated sulphuric acid.

The nitro compound layer is washed with warm water, then with a warm dilute

solution of sodium carbonate and again with warm water. The washed nitro com-

pound is dried by heating under reduced pressure. From 100 kg of p- chloronitro-

benzene 128.5 kg of 1-chloro-2,4-dinitrobenzene is obtained, which is 98.5% of the

theoretical yields.

NITRATION OF CHLOROBENZENE TO CHLORODINITROBENZENE

(GRIESHEIM METHOD)

The nitration of chlorobenzene to chlorodinitrobenzene without separating

the isomers of chloronitrobenzene is accomplished in two successive stages in the

same nitrator.

Mononitration. 3000 kg of chlorobenzene, boiling within a range of 0.8°C,

is mixed with the spent acid from dinitration, containing 78% of H 2 SO 4. Then

1850 kg of a nitrating mixture of the compositions :

HNO 3 87-88%

H 2 SO 4 11%