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244 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

In 1933, Hetherington and Masson [33] made a systematic study of nitration

of nitrobenzene to dinitrobenzene using a wide range of mixtures of sulphuric

and nitric acids and water. They plotted their results on a curve of “limiting com-

positions” beyond which the reaction does not occur (Fig. 27, p. 154). They also

showed the change in molar composition of the acid during nitration (Fig. 48).

For example, an acid of initial composition will nitrate nitrobenzene until its com-

position moving along the parallel XY reaches Y, when it practically ceases to

react. Figure 49 gives the molar compositions of the acid present in both the organic

and acid layer. The rate of nitration was given in Fig. 28 (p. 155).

In practice, for the nitration of nitrobenzene, a nitrating. mixture of the com-

position:

HNO 3 18%

H 2 SO 4 80%

H 2 O 2%

is generally used, in about 10% excess over the theoretical amount.

Pure o- and p- dinitrobenzenes may be obtained from the corresponding nitro-

anilines in two ways: either by diazotization (Meisenheimer and Patzig [34],) or

by oxidation (Bamberger and Hübner [35], Witt and Kopetschni [36]):

(7)

(8)

Nitration in two stages in two nitrators. In industrial practice the preparation
of dinitrobenzene is commonly carried out by nitration in two stages:

Benzene -> Nitrobenzene -> Dinitrobenzene

In this way, operating conditions are safer during the process and acid con-

trol can be made more efficient.

The first operation, i.e. the nitration of benzene to nitrobenzene, has been al-

ready described (pp. 232, 233). The second stage of the process, i.e. the nitration
of nitrobenzene to dinitrobenzene by the method used at Höchst (I. G. Farben-

industrie) is described below.
Nitrobenzene is pumped into a measuring tank of 5 m^3 capacity, lined with

sheet lead. 3660 kg of nitrobenzene is fed from the tank to a nitrator of 10 m

3