The synthesis of p-nitroaniline from aniline and nitric acid is an electrophilic aromatic substitution reaction, specifically nitration. The optimal reaction conditions for this reaction are as follows:1. Reagents: Aniline C6H5NH2 and concentrated nitric acid HNO3 .2. Catalyst: Concentrated sulfuric acid H2SO4 is used as a catalyst to generate the nitronium ion NO2+ , which is the electrophile in this reaction.3. Temperature: The reaction should be carried out at low temperatures, ideally between 0-5C. This is because the reaction is highly exothermic, and higher temperatures can lead to the formation of undesired by-products, such as dinitroaniline.4. Reaction time: The reaction should be allowed to proceed for a sufficient amount of time, typically 1-2 hours, to ensure complete conversion of aniline to p-nitroaniline.To measure and improve the purity of the final product, the following steps can be taken:1. Recrystallization: After the reaction is complete, the crude product can be purified by recrystallization. This involves dissolving the crude product in a suitable solvent, such as ethanol or water, and then slowly cooling the solution to allow the pure p-nitroaniline to crystallize out. The impurities remain dissolved in the solvent and can be separated by filtration.2. Column chromatography: If further purification is required, column chromatography can be used to separate p-nitroaniline from any remaining impurities. This involves passing the crude product through a column packed with a stationary phase, such as silica gel or alumina, and eluting with a suitable solvent or solvent mixture. The p-nitroaniline and impurities will have different affinities for the stationary phase and will be separated as they travel through the column.3. Melting point determination: The purity of the final product can be assessed by measuring its melting point and comparing it to the known melting point of pure p-nitroaniline approximately 147C . A narrow melting point range close to the literature value indicates a high degree of purity.4. Spectroscopic techniques: Techniques such as infrared IR spectroscopy, nuclear magnetic resonance NMR spectroscopy, and mass spectrometry can be used to confirm the identity and purity of the final product. These techniques provide information about the molecular structure and composition of the compound, allowing for the identification of any remaining impurities.