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NITRO DERIVATIVES OF HIGHER BENZENE HOMOLOGUES 407

Nitrating mixture of a composition:

HNO 3 18-19%

H 2 SO 4 78-79%

H 2 O 3%

is run into the nitrator. Then the stirrer (120-150 r. p. m.) is started and cooling

water is passed through the jacket and the coil of the nitrator. When the temperature

reaches 12°C xylene is run into the nitrator at such a rate as to allow the whole

quantity to be introduced in 4-4.5 hr (for 1 part by weight of xylene 13.5 parts

of the nitrating mixture is applied). Thus, the excess of nitric acid used amounts

to 43%). During the introducing of the xylene a temperature of 30-40°C is main-

tained, and by the end of the operation it is raised to 65-70°C.

When all the xylene has been run into the nitrator the temperature rises spon-

taneously to 90°C. This is a critical moment, as the rise of temperature is accom-

panied by vigorous oxidation and frothing of the reaction mixture, owing to the

evolution of gases (mainly carbon dioxide and nitrogen oxides). The reaction mixture

is likely to run over if the process is too vigorous. When the violent reaction has

subsided the mixture is heated to 105°C, this temperature being maintained for

one hour.

The whole operation takes nearly 7 hr, including half an hour for charging

the nitrator, 6 hr for the nitration, and half an hour for unloading.

After nitration has been completed the mixture is sent to a settler and allowed

to remain there for 2 hr for the nitro compound to settle. The product is separated

from the spent acid on a vacuum filter, and then transferred by means of shovels

or by a stream of water to a washing tank.

The composition of the spent acid is:

HNO 3 0.8-1.5%

NO 2 3-5%

H 2 SO 4 81-82.5%

nitro compounds 3-4.5%

H 2 O 8-11%

Trinitroxylene is washed in a lead-lined wooden tank (Fig. 103) first several
limes with cold water (1 part of water for 1 part of the product), then with hot water

(80-85°C) and finally with cold water again. In all, the washing is repeated 6-7

times, each washing taking about 1 hr.

Compressed air, introduced through a lead bubbler, is used for mixing the nitro

compound with water.

When the acid content of the washings falls below 0.1%, the product together

with the washing water is drained off to a centrifuge. At this stage the trinitroxylene

still contains oily admixtures apart from water.

When heated, it melts partially at 120-125°C, and becomes completely molten

at 160-177°C. The melting point of the main part of the product is 163°C.

By passing moist hot trinitroxylene through a centrifuge not only the water

but also the oily components are removed. Under these circumstances the product