The Chemistry of Powder and Explosives - Sciencemadness Dot Org

126 AROMATIC NITRO COMPOUNDS
phenols, cresol, xylenol, etc., where they reduce the toxicity of
the substances but increase their antiseptic strength.
In the manufacture of explosives the nitro groups are always
introduced by the direct action of nitric acid on the aromatic
substances. The simple reaction involves the production of water
and is promoted by the presence of sulfuric acid which thus
functions as a dehydrating agent. We shall later see cases in
which sulfuric acid is used as a means of hindering the introduction
of nitro groups. In consequence of the reaction, the nitrogen
atom of the nitro group becomes attached to the carbon atom of
the aromatic nucleus. Nitro groups attached to the nucleus,
unless ortho and para to other nitro groups, are not affected by
sulfuric acid as are nitro groups attached to oxygen (in nitric
esters) and to nitrogen (in nitroamines), or, ordinarily, by hydrolytic
agents as are nitro groups attached to oxygen. Nitric acid
is a nitrating agent both at low and at elevated temperatures;
its vigor in this respect depends upon the concentration. But
it is an oxidizing agent even in fairly dilute solution, and becomes
more vigorous if the temperature is raised. Further, it decomposes
when heated to produce nitrous acid, which is also a powerful
oxidizing agent and may reduce the yield of the desired
product. Nitrous acid present in the nitrating acid may also
result in the formation of nitrophenols from aromatic amines.
Aromatic nitro compounds, such as TNT and picric acid, on
refluxing for some hours with nitric acid id. 1.42) and then
distilling the mixture, yield appreciable quantities of tetranitromethane,
formed by the rupture of the ring and the nitration of
the individual carbon atoms. The nitro group "strengthens" the
ring against attack by acid oxidizing agents, but makes it more
accessible to attack by alkaline ones. The polynitro compounds
are destroyed rapidly by warm alkaline permanganate yielding
oxalic acid. They combine with aniline, naphthylamine, etc., to
form brightly colored molecular compounds. All aromatic nitro
compounds give colors, yellow, orange, red, even purple, with
alkaline reagents.
The position which the nitro group takes on entering the
aromatic nucleus and the ease with which the substitution is
accomplished depend upon the group or groups already present