The preparation of 2-chloro-4-nitroaniline from aniline and chlorine gas involves a two-step process: nitration followed by chlorination. Here is the stepwise 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 sulfuric acid to form the nitronium ion NO2+ , which is the active electrophile in the nitration process.HNO3 + 2H2SO4 NO2+ + H3O+ + 2HSO4-1.3. Electrophilic aromatic substitution: The nitronium ion NO2+ reacts with the anilinium ion C6H5NH3+ via electrophilic aromatic substitution, resulting in the formation of 4-nitroaniline C6H4 NO2 NH3+ .C6H5NH3+ + NO2+ C6H4 NO2 NH3+1.4. Deprotonation: The 4-nitroaniline is deprotonated to form the neutral product.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+ reacts with 4-nitroaniline C6H4 NO2 NH2 via electrophilic aromatic substitution, resulting in the formation of 2-chloro-4-nitroaniline C6H3 NO2 NH2Cl .C6H4 NO2 NH2 + Cl+ C6H3 NO2 NH2ClOptimum conditions for maximum yield:- For the nitration step, use a mixture of concentrated nitric acid HNO3 and concentrated sulfuric acid H2SO4 as the nitrating agent. The reaction should be carried out at low temperatures 0-5C to minimize the formation of undesired products.- For the chlorination step, use a catalytic amount of ferric chloride FeCl3 to activate the chlorine gas. The reaction should be carried out at low temperatures 0-5C and in an inert atmosphere e.g., nitrogen to minimize side reactions and decomposition of the product.It is important to note that the nitration of aniline can lead to the formation of multiple products, and the reaction conditions should be carefully controlled to obtain the desired 4-nitroaniline. Additionally, the chlorination step may also result in the formation of other isomers, so purification steps such as recrystallization or chromatography may be necessary to obtain the desired 2-chloro-4-nitroaniline with high purity.