The preparation of 2-chloro-4-nitroaniline from aniline and chlorine gas involves a two-step process: nitration followed by chlorination. Here's the complete mechanism:Step 1: Nitration of aniline1. Protonation of aniline: Aniline C6H5NH2 reacts with a strong acid, such as concentrated sulfuric acid H2SO4 , to form the anilinium ion C6H5NH3+ .C6H5NH2 + H2SO4 -> C6H5NH3+ + HSO4-2. Formation of nitronium ion: Concentrated nitric acid HNO3 reacts with the sulfuric acid to form the nitronium ion NO2+ , which is the active electrophile in the nitration process.HNO3 + 2H2SO4 -> NO2+ + H3O+ + 2HSO4-3. Electrophilic aromatic substitution: The nitronium ion NO2+ attacks the anilinium ion at the para position, forming a para-nitroaniline intermediate.C6H5NH3+ + NO2+ -> C6H4 NH3+ NO2 + H+4. Deprotonation: The para-nitroaniline intermediate loses a proton to form para-nitroaniline p-nitroaniline, C6H4 NH2 NO2 .C6H4 NH3+ NO2 + HSO4- -> C6H4 NH2 NO2 + H2SO4Step 2: Chlorination of p-nitroaniline1. Activation of chlorine gas: Chlorine gas Cl2 is activated in the presence of a Lewis acid catalyst, such as aluminum chloride AlCl3 , to form a chloronium ion Cl+ .Cl2 + AlCl3 -> Cl+ + AlCl4-2. Electrophilic aromatic substitution: The chloronium ion Cl+ attacks the p-nitroaniline at the ortho position, forming an ortho-chloro-p-nitroaniline intermediate.C6H4 NH2 NO2 + Cl+ -> C6H3 NH2 NO2 Cl + H+3. Rearrangement: The ortho-chloro-p-nitroaniline intermediate rearranges to form the more stable 2-chloro-4-nitroaniline C6H3 NH2 NO2 Cl .C6H3 NH2 NO2 Cl -> 2-chloro-4-nitroanilineThe final product is 2-chloro-4-nitroaniline.