The synthesis of 2,4-dichlorobenzoic acid from benzoic acid and chlorine gas can be achieved through electrophilic aromatic substitution, specifically chlorination. To obtain the highest yield with the least amount of side products, the reaction conditions should be optimized.Optimum reaction conditions for this synthesis are:1. Temperature: The reaction should be carried out at a temperature of around 0C to 10C. Lower temperatures help minimize the formation of side products, such as over-chlorinated compounds, and favor the formation of the desired 2,4-dichlorobenzoic acid.2. Pressure: The reaction can be performed under atmospheric pressure. However, if the reaction is sluggish, a slight increase in pressure 1-2 atm can be applied to improve the reaction rate.3. Duration of the reaction: The reaction time depends on the efficiency of the catalyst and the reaction conditions. Generally, the reaction can take anywhere from 2 to 6 hours. It is essential to monitor the reaction progress using techniques such as thin-layer chromatography TLC or gas chromatography GC to determine the optimal reaction time.4. Catalyst: A Lewis acid catalyst, such as aluminum chloride AlCl3 or ferric chloride FeCl3 , is required to facilitate the electrophilic aromatic substitution. The catalyst should be used in a stoichiometric or slightly excess amount to ensure complete conversion of benzoic acid to the desired product.In summary, the optimum reaction conditions for the synthesis of 2,4-dichlorobenzoic acid from benzoic acid and chlorine gas are a temperature of 0C to 10C, atmospheric pressure or slightly higher if needed , and a reaction time of 2 to 6 hours, depending on the catalyst efficiency and reaction progress.