The preparation of 2,4-dichloronitrobenzene from nitrobenzene and chlorine gas can be achieved through electrophilic aromatic substitution. The optimal reaction conditions and yield are as follows:1. Catalyst: A Lewis acid catalyst, such as aluminum chloride AlCl3 or ferric chloride FeCl3 , is required to facilitate the chlorination reaction.2. Reaction temperature: The reaction should be carried out at a temperature of 0-5C to control the rate of reaction and minimize the formation of undesired by-products.3. Reaction time: The reaction time can vary depending on the specific conditions, but generally, it should be allowed to proceed for several hours to ensure complete conversion of nitrobenzene to 2,4-dichloronitrobenzene.4. Solvent: A non-polar solvent, such as carbon tetrachloride CCl4 or dichloromethane CH2Cl2 , can be used to dissolve the reactants and facilitate the reaction.5. Reaction stoichiometry: The stoichiometry of the reaction should be controlled to ensure the formation of the desired product. Typically, a slight excess of chlorine gas 1.1-1.2 equivalents is used to ensure complete conversion of nitrobenzene to 2,4-dichloronitrobenzene.6. Yield: The yield of 2,4-dichloronitrobenzene can vary depending on the specific reaction conditions, but under optimal conditions, yields of 70-80% can be achieved.It is important to note that the reaction should be carried out under anhydrous conditions to prevent the formation of undesired side products. Additionally, proper safety precautions should be taken when handling chlorine gas, as it is highly toxic and corrosive.