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(^92) CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES
However, a homolytic dissociation into free radicals NO 2 is possible:
N 2 O 4 <-> 2NO 2 (19)
This has been confirmed by experiments on the addition of N 2 O 4 to asym-
metrically substituted olefins (Shechter and Conrad [49]). The most recent
review of the chemistry of nitrogen dioxide is that of Gray and Yoffe [50]
published in 1955.
The experiments of Falecki, Mint, Slebodzinski and T. Urbanski [185a] men-
tioned below also suggest that under the action of γ− radiation dinitrogen tetroxide
is split mainly into ions NO 2 + or (even more likely) into free radicals .NO 2 (accord-
ing to eqn. 19).
NITRATION WITH NITROGEN DIOXIDE ALONE
Aromatic compounds
The nitration of aromatic compounds with nitrogen dioxide was mentioned
by Hasenbach [51] as early as 1871. He observed that when treating benzene with
N 2 O 4 (N 2 O 4 <-> 2NO 2 ) at room temperature for 7 days, nitrobenzene was formed
along with oxalic acid. Leeds [52] also found picric acid in the reaction products.
On treating toluene with N 2 O 4 he obtained nitro derivatives of phenols and benzoic
acid apart from nitrotoluenes. Naphthalene was nitrated similarly to give nitro
and hydroxynitro derivatives.
When nitrating anthracene with N 2 O 4 at a temperature of 10-15°C Liebermann
and Lindermann [53] obtained nitro derivatives of this hydrocarbon.
Meisenheimer’s observation [54], in 1904, that anthracene combined with
nitrogen dioxide to form meso-dihydrodinitroanthracene, was of special import-
ance :
(20)
It inspired Wieland [55] in 1921 to investigate the possibility of nitrating aro-
matic compounds with nitrogen dioxide.
When studying the action of nitrogen dioxide on benzene at 80°C Wieland
found 1,3,5-trinitrobenzene and picric acid were present along with oxidation
products (oxalic acid, CO 2 ). Nitrobenzene was not obtained in the reaction and
a large quantity of benzene remained unconverted. Wieland tried to explain this
by assuming that in the first stage of the reaction six molecules of NO 2 combine
with benzene just as chlorine or bromine do under the influence of light. The hexa-
nitrocyclohexane thus formed gives off three HNO 2 molecules to form 1,3,5-tri-
nitrobenzene :