The preparation of 2,4-dichlorobenzoic acid from benzoic acid and chlorine gas can be achieved through the following step-by-step procedure:1. Selection of solvent and catalyst: Choose a suitable solvent and catalyst for the reaction. A common solvent for this reaction is carbon tetrachloride CCl4 , and the catalyst is typically anhydrous ferric chloride FeCl3 .2. Preparation of the reaction mixture: In a round-bottom flask, dissolve an appropriate amount of benzoic acid C6H5COOH in carbon tetrachloride. The amount of benzoic acid used will depend on the desired scale of the reaction.3. Addition of the catalyst: Add a catalytic amount of anhydrous ferric chloride FeCl3 to the reaction mixture. The catalyst will facilitate the electrophilic aromatic substitution reaction between benzoic acid and chlorine gas.4. Purging with chlorine gas: Slowly introduce chlorine gas Cl2 into the reaction mixture while stirring. The chlorine gas should be bubbled through the solution to ensure proper mixing. The reaction mixture will turn yellowish-green as the reaction proceeds.5. Monitoring the reaction: Monitor the reaction progress using thin-layer chromatography TLC or another suitable analytical technique. The reaction is complete when the starting benzoic acid is no longer detectable, and the desired 2,4-dichlorobenzoic acid product is observed.6. Quenching the reaction: Once the reaction is complete, quench the reaction mixture by adding water or another suitable quenching agent. This will neutralize any remaining catalyst and help to separate the organic and aqueous layers.7. Extraction and purification: Separate the organic layer containing the product from the aqueous layer. The organic layer can be washed with water and brine to remove any remaining impurities. The solvent can then be removed under reduced pressure using a rotary evaporator, leaving behind the crude 2,4-dichlorobenzoic acid product.8. Recrystallization: To further purify the product, dissolve the crude 2,4-dichlorobenzoic acid in a suitable solvent, such as hot ethanol or ethyl acetate, and then allow the solution to cool slowly. The purified 2,4-dichlorobenzoic acid will crystallize out of the solution as it cools.9. Isolation and drying: Collect the purified 2,4-dichlorobenzoic acid crystals by vacuum filtration and allow them to dry.The yield of 2,4-dichlorobenzoic acid obtained from this reaction can vary depending on the reaction conditions, the purity of the starting materials, and the efficiency of the purification steps. Typical yields for this reaction can range from 60-80%.