The preparation of 2-chloro-4-nitroaniline from aniline and chlorine gas involves a two-step process: nitration followed by chlorination. Here is the mechanism for each step:1. Nitration of aniline:Aniline C6H5NH2 is first nitrated to form 4-nitroaniline C6H4 NO2 NH2 . This is done by treating aniline with a mixture of concentrated nitric acid HNO3 and concentrated sulfuric acid H2SO4 . The reaction proceeds as follows:a. Formation of nitronium ion NO2+ : HNO3 reacts with H2SO4 to form the nitronium ion, which is the electrophile in this reaction.HNO3 + H2SO4 NO2+ + HSO4- + H2Ob. Electrophilic aromatic substitution: The nitronium ion NO2+ attacks the aromatic ring of aniline, resulting in the formation of 4-nitroaniline.C6H5NH2 + NO2+ C6H4 NO2 NH22. Chlorination of 4-nitroaniline:4-nitroaniline is then treated with chlorine gas Cl2 in the presence of a catalyst, such as ferric chloride FeCl3 , to form 2-chloro-4-nitroaniline C6H3Cl NO2 NH2 . The reaction proceeds through electrophilic aromatic substitution:a. Formation of Cl+: Chlorine gas reacts with the catalyst FeCl3 to form the electrophilic species Cl+.Cl2 + FeCl3 2Cl+ + FeCl4-b. Electrophilic aromatic substitution: The Cl+ attacks the aromatic ring of 4-nitroaniline, resulting in the formation of 2-chloro-4-nitroaniline.C6H4 NO2 NH2 + Cl+ C6H3Cl NO2 NH2Parameters crucial for the success of the reaction:1. Temperature: Nitration of aniline is an exothermic reaction, and controlling the temperature is essential to avoid the formation of undesired by-products. The reaction is typically carried out at low temperatures 0-10C to ensure the formation of the desired product.2. Pressure: Chlorination with chlorine gas is usually performed under atmospheric pressure. However, increasing the pressure can enhance the reaction rate and improve the yield of the desired product.3. Catalyst: The use of a catalyst, such as ferric chloride FeCl3 , is crucial for the chlorination step. The catalyst activates the chlorine gas, generating the electrophilic species Cl+ required for the reaction.4. Reaction time: The nitration step is relatively fast, while the chlorination step may require a longer reaction time to achieve a good yield of the desired product. The reaction time should be optimized for each step to ensure the formation of 2-chloro-4-nitroaniline.