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274 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

For TNT manufacture the presence of m- nitrotoluene in mononitrotoluene

is naturally undesirable, as it is a source of unsymmetrical trinitrotoluenes.

Therefore, it would be preferable to apply a nitration method in which the

m- isomer would not be formed at all, or only in an insignificant quantity. But as

Table 50 indicates, this is impossible to achieve by nitrating with a mixture of

nitric and sulphuric acids.

The fact that in the nitration of toluene with a solution of nitric acid in acetic

anhydride, a mixture of 88% of o- and 12% of p- nitrotoluene, i.e. a mixture free

from m- nitrotoluene, can been obtained, has been mentioned in the literature only

once (Pictet and Khotinsky [15]).

T. Urbanski and his co-workers [16] recently confirmed this observation and

reported the following nitration conditions:

composition of the nitrating mixture 68% of acetic anhydride

32% of nitric acid

excess of nitrating mixture (calculated on HNO 3 ) 10%

temperature of nitration 10°C

nitration period 2hr

The mixture of o- and p- nitrotoluene they obtained was free from the m- isomer.

The authors used it for further nitration, and found that the resulting trinitro-

toluene was of much higher purity than that produced from mononitrotoluene

according to the conventional industrial method.

An interesting method of reducing the proportion of m- nitrotoluene was de-

veloped by Orlova [2a]. It consists in adding sodium nitrite to the nitrating mix-

ture. The results of these experiments are given in Table 51.

The nitration was carried out using acid with 10% HNO 3 , for 100 min at 55°C.

TABLE 51

% NaNO 2 0 1.5 3.0 4.5 5.9 8.6 11.0

Proportion of m- nitro-

toluene 5.4 4.3 4.1 3.5 2.8 2.1 2.6

Setting point of TNT, °C 78.0 78.6 78.75 78.75 78.93 78.2 77.9

Recently Kobe and Lakemeyer [17] drew attention to the fact that nitrating

mixtures used for mononitration of toluene prepared spent acid from trinitration

contain 14-17 wt. % of nitrosylsulphuric acid. They investigated the influence of

nitrosylsulphuric acid, SO 2 (OH)ONO, on the rate of mononitration of toluene. The

rate at 35°C is at a maximum at ca. 4.0 mole % of nitrosylsulphuric acid.

More dilute nitric acid, when used for nitration, favours side reactions, prima-

rily oxidation reactions, yielding benzoic acid. According to Konovalov [18], if

a 70% nitric acid (sp. gr. 1.42) is used for the nitration of toluene, nothing but

benzoic acid is formed.