The most efficient method for preparing p-nitroaniline from aniline and nitric acid is through a process called nitration. Nitration is an electrophilic aromatic substitution reaction where a nitro group -NO2 is introduced to the aromatic ring of aniline. The reaction proceeds as follows:Aniline C6H5NH2 + HNO3 nitric acid p-Nitroaniline C6H4 NO2 NH2 + H2O water To carry out this reaction, aniline is first converted to its acetate salt by reacting it with acetic acid. This step is crucial because it protects the amino group from being oxidized by nitric acid and also deactivates the aniline ring, making it less reactive towards electrophilic substitution. The reaction is as follows:Aniline C6H5NH2 + CH3COOH acetic acid C6H5NH3+CH3COO- anilinium acetate Next, a nitrating mixture is prepared by mixing concentrated nitric acid with concentrated sulfuric acid. The anilinium acetate is then added to this nitrating mixture, which results in the formation of p-nitroaniline. The reaction is as follows:C6H5NH3+CH3COO- anilinium acetate + HNO3 nitric acid p-Nitroaniline C6H4 NO2 NH2 + CH3COOH acetic acid + H2O water Factors affecting the yield and purity of the final product:1. Temperature: The nitration reaction is highly exothermic. It is essential to maintain a low temperature 0-5C during the reaction to prevent the formation of undesired by-products such as dinitroaniline or other isomers. An ice bath can be used to control the temperature.2. Concentration of reagents: The use of concentrated nitric and sulfuric acids is crucial for the formation of the nitronium ion NO2+ , which acts as the electrophile in the reaction. Dilute acids will result in lower yields.3. Reaction time: The reaction should be allowed to proceed until completion to ensure maximum yield. However, overexposure to the nitrating mixture can lead to the formation of undesired by-products.4. Purification: The crude product obtained after the reaction may contain impurities such as unreacted aniline, o-nitroaniline, and other by-products. To obtain pure p-nitroaniline, the crude product can be purified using techniques such as recrystallization from a suitable solvent e.g., hot water or ethanol .By carefully controlling these factors, it is possible to obtain a high yield and purity of p-nitroaniline from aniline and nitric acid.