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 .