The preparation of 2-chloro-4-nitroaniline from aniline and chlorine gas involves a two-step process: nitration followed by chlorination. Here is the step-wise mechanism for this reaction:Step 1: Nitration of aniline1.1 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+ + HSO4-1.2 Formation of nitronium ion: Concentrated nitric acid HNO3 reacts with the protonated sulfuric acid to form the nitronium ion NO2+ , which is the electrophile in the nitration reaction.HNO3 + 2H2SO4 NO2+ + H3O+ + 2HSO4-1.3 Electrophilic aromatic substitution: The nitronium ion NO2+ attacks the anilinium ion C6H5NH3+ at the para position due to the activating effect of the amino group to form 4-nitroaniline C6H4 NO2 NH3+ .C6H5NH3+ + NO2+ C6H4 NO2 NH3+1.4 Deprotonation: The 4-nitroaniline is deprotonated by the bisulfate ion HSO4- to form the neutral 4-nitroaniline C6H4 NO2 NH2 .C6H4 NO2 NH3+ + HSO4- C6H4 NO2 NH2 + H2SO4Step 2: Chlorination of 4-nitroaniline2.1 Activation of chlorine: Chlorine gas Cl2 is activated in the presence of a catalyst, such as ferric chloride FeCl3 , to form the electrophilic chlorine ion Cl+ .Cl2 + FeCl3 2Cl+ + FeCl4-2.2 Electrophilic aromatic substitution: The electrophilic chlorine ion Cl+ attacks the 4-nitroaniline C6H4 NO2 NH2 at the ortho position due to the deactivating effect of the nitro group to form 2-chloro-4-nitroaniline C6H3 NO2 NH2Cl .C6H4 NO2 NH2 + Cl+ C6H3 NO2 NH2ClThe final product is 2-chloro-4-nitroaniline C6H3 NO2 NH2Cl .