1. Introduction
The nitration of aromatics is one of the oldest and most ubiquitous
reactions utilized in industrial production and laboratory research.
Similar to the nitration of benzene and toluene,1,2the nitration of chlorobenzene (CB) is representative, and its products
are important raw materials and intermediates, that are widely applied
in dyes, pharmaceuticals, explosives, pesticides, and
spices.3 Generally, the nitration of aromatics is a
liquid-liquid heterogeneous reaction. The reaction mainly takes place in
the acid phase containing a large excess of sulfuric acid, and the
amount of nitric acid is stoichiometrically proportional to that of the
aromatic hydrocarbons. Taking the nitration of CB as an example, when
nitric acid reacts with sulfuric acid, its hydroxyl group is protonated,
and a molecule of water is removed to form nitronium ions (). The
general consensus that is the true nitrating agent in the
nitration.4 CB molecules diffuse into the acid phase
and undergo an electrophilic substitution reaction with nitronium ions
to generate three isomers: 1-chloro-2-nitrobenzene (o -NCB),
1-chloro-4-nitrobenzene (p -NCB), and a very small amount of
1-chloro-3-nitrobenzene (m -NCB). These isomers can further react
with nitronium ions to form the secondary nitration product
1-chloro-2,4-dinitrobenzene (DNCB). The reactions are shown inScheme 1 .