The preparation of 2,4-dinitrophenylhydrazine DNPH from hydrazine and 2,4-dinitrochlorobenzene involves a nucleophilic aromatic substitution reaction. The specific reaction mechanism and stoichiometry are as follows:1 Nucleophilic attack of hydrazine N2H4 on 2,4-dinitrochlorobenzene C6H3Cl NO2 2 to form an intermediate.2,4-dinitrochlorobenzene + hydrazine intermediate2 Loss of chloride ion Cl- from the intermediate to form 2,4-dinitrophenylhydrazine.Intermediate 2,4-dinitrophenylhydrazine + Cl-Overall reaction:C6H3Cl NO2 2 + N2H4 C6H3 NO2 2N2H3 + Cl-The stoichiometry of the reaction is 1:1, meaning one mole of 2,4-dinitrochlorobenzene reacts with one mole of hydrazine to produce one mole of 2,4-dinitrophenylhydrazine and one mole of chloride ion.To optimize the synthesis process for higher yields and purity, consider the following steps:1. Temperature control: The reaction should be carried out at low temperatures 0-5C to minimize side reactions and decomposition of hydrazine.2. Use of excess hydrazine: Adding an excess of hydrazine can help drive the reaction to completion, ensuring maximum conversion of 2,4-dinitrochlorobenzene to DNPH.3. Proper mixing: Ensure thorough mixing of the reactants to facilitate the nucleophilic attack and improve the reaction rate.4. Purification: After the reaction is complete, the product can be purified by recrystallization from a suitable solvent, such as ethanol or ethyl acetate. This will help remove any unreacted starting materials and impurities, resulting in a higher purity product.5. Monitoring the reaction: Use analytical techniques such as thin-layer chromatography TLC or high-performance liquid chromatography HPLC to monitor the progress of the reaction and determine the optimal reaction time for maximum yield and purity.