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NITRO DERIVATIVES OF NAPHTHALENE^443

French method

The nitration of naphthalene to dinitronaphthalene (after Pascal [20a]) is effected

in a nitrator essentially of the same type as that used for the nitration of naphthalene
to nitronaphthalene by the French method (Fig. 108, p. 441), the only difference
being in the outlet which is wider at the bottom - 8 cm in diameter - since the

nitration product is solid.

The nitrator is charged with 1060 kg of a nitrating mixture of the composition:

HNO 3 23-24%

H 2 SO 4 54-55%

H 2 O 21-21.5%

Then finely ground and sifted naphthalene is added at a rate which at the beginning

is about 50 kg/hr, and by the end 35-40 kg/hr. During the addition of naphthalene

the temperature is controlled by cooling, so that it does not exceed 55°. By the end

of the process the mixture has heated up to 70°C.

After the completion of the reaction, the nitrator contents are discharged into

a lead vacuum filter of 1000 1. capacity for separating the product from the spent

acid. The spent acid has the composition:

HNO 3 0.5-1.5%

NO 2 1.5-2.5%

H 2 SO 4 62-63%

H 2 O 33-35%

organic matter ca. 1.5%

The product is washed as described below (see preparation of dinitronaphthalene

from nitronaphthalene).

NITRATION OF NITRONAPHTHALENE TO DINITRONAPHTHALENE

French method

As Pascal [20a] reports, the reaction is carried on in the following way. The

nitrator is fed with 1150 kg of a nitrating mixture of the composition:

HNO 3 26.5%

H 2 SO 4 51%

H 2 O 22.5%

Then during 3-4 hr 400 kg of α− nitronaphthalene is added in lumps obtained

by breaking with a hammer the product of mononitration. The temperature is main-

tained within the range 38-45°C by cooling. A ternary eutectic formed by α− nitro-

naphthalene and 1,5- and 1,8-dinitronaphthalenes melts within the range 44-54°C,

So that at this stage of the process the substance being nitrated is in a molten state,

thus facilitating nitration. A stirrer keeps the substance in suspension in the form

of drops of l-2 mm in diameter.

After all the nitronaphthalene has been added, the temperature is raised to 55°C

within one hour, and then cooled to 40°C. The dinitronaphthalene solidifies in the

form of granules.