The preparation of 2-chloro-4-nitroaniline from aniline and chlorine gas can be achieved through a two-step process: nitration followed by chlorination. Here is the step-by-step reaction mechanism:Step 1: Nitration of Aniline1.1. Protonation of aniline:Aniline C6H5NH2 reacts with a strong acid, such as 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 sulfuric acid H2SO4 to form the nitronium ion NO2+ , which is the active electrophile in the nitration process.HNO3 + H2SO4 -> NO2+ + HSO4- + H2O1.3. Electrophilic aromatic substitution:The nitronium ion NO2+ reacts with the anilinium ion C6H5NH3+ through an electrophilic aromatic substitution reaction, resulting in the formation of 4-nitroaniline C6H4 NO2 NH3+ .C6H5NH3+ + NO2+ -> C6H4 NO2 NH3+Step 2: Chlorination of 4-Nitroaniline2.1. Activation of chlorine gas: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 through an electrophilic aromatic substitution reaction, resulting in the formation of 2-chloro-4-nitroaniline C6H3 NO2 NH2Cl .C6H4 NO2 NH2 + Cl+ -> C6H3 NO2 NH2ClOptimal conditions for high conversion rate:1. Nitration:- Use concentrated sulfuric acid H2SO4 and concentrated nitric acid HNO3 as the nitrating agents.- Maintain a low temperature 0-5C to control the reaction rate and minimize the formation of undesired products.2. Chlorination:- Use a catalyst like ferric chloride FeCl3 to activate the chlorine gas.- Maintain a low temperature 0-5C to control the reaction rate and minimize the formation of undesired products.- Use an excess of chlorine gas to drive the reaction to completion.It is important to note that the reaction conditions should be carefully controlled to minimize the formation of undesired products, such as 2,4-dichloroaniline or other isomers.