CHAPTER VIIINITRO DERIVATIVES OF TOLUENE
ONE, two, or three nitro groups can be introduced by direct nitration of toluene.
Tetranitrotoluene can be obtained only by indirect methods.
Of all nitro derivatives of toluene, trinitrotoluene is the most important as an
explosive. It is by far the most often used high explosive among those derived
from aromatic compounds. It is popular because it is simple and relatively safe to
manufacture, and has high explosive power, and above all because its high chemical
stability and low sensitiveness to impact and friction make it safe to handle. In
addition, its toxicity is low and thus it compares favourably in this respect with
the nitro derivatives of benzene.
NITRATION OF TOLUENE
Nitration of toluene has this specific feature: the presence of a methyl group
greatly facilitates the nitration as compared with benzene. The reaction of intro-
ducing the first nitro group therefore proceeds very quickly. In addition to this.
the methyl group is readily oxidized. Mononitration results in the oxidation of
the ring and the formation of cresols (as in the case of benzene, which is oxidized
to phenol). The oxidation reactions proceed especially readily under drastic con-
ditions which introduce several nitro groups at a high temperature.
Sometimes, for example, if the nitration mixture is poor in nitric acid, tar
formation may take place readily. It may also occur if an insufficient amount of
the nitration mixture (calculated on HNO 3 ) has been used for the nitration. For
this reason it is preferable to use mixtures richer in HNO 3 , and to use a distinct
excess of the nitrating mixture. On the other hand, both these factors (high con-
tent of HNO 3 , and excess of nitrating mixture) favour oxidation processes in
practice; therefore, limits are applied, i.e. nitrating mixtures should not be too
rich in HNO 3 , and a very slight excess (e.g. 1-2%) of it should be used.
Kostevich and Sapozhnikov [1] have carried out extensive studies on the nitra-
tion of toluene to mononitrotoluene, using nitrating mixtures of various compositions
and determining the composition of mixtures leading to dinitrotoluene. All the
reactions were carried out under similar conditions. The results are given in a