The preparation of 2,4-dichlorobenzoic acid from benzoic acid and chlorine gas can be achieved through the following steps:Step 1: Chlorination of benzoic acidIn this step, benzoic acid reacts with chlorine gas in the presence of a catalyst, such as ferric chloride FeCl3 , to form 2,4-dichlorobenzoic acid. The reaction can be represented as follows:C6H5COOH + 2 Cl2 C6H3Cl2COOH + 2 HClReagents required:1. Benzoic acid C6H5COOH 2. Chlorine gas Cl2 3. Ferric chloride FeCl3 as a catalystConditions required:1. Temperature: The reaction is typically carried out at room temperature or slightly above.2. Solvent: A suitable solvent, such as carbon tetrachloride CCl4 or chloroform CHCl3 , can be used to dissolve the reactants and facilitate the reaction.Yield: The yield of 2,4-dichlorobenzoic acid depends on the reaction conditions, the purity of the starting materials, and the efficiency of the catalyst. In general, the yield can range from 60-80%.Step 2: Isolation and purification of 2,4-dichlorobenzoic acidAfter the chlorination reaction is complete, the reaction mixture contains 2,4-dichlorobenzoic acid, unreacted benzoic acid, and by-products such as hydrogen chloride HCl . To isolate and purify the desired product, the following steps can be performed:1. Filtration: Filter the reaction mixture to remove any undissolved solids, such as the catalyst.2. Acidification: Add a dilute acid, such as hydrochloric acid HCl , to the filtrate to protonate the carboxylate ions and precipitate the 2,4-dichlorobenzoic acid.3. Filtration: Filter the precipitated 2,4-dichlorobenzoic acid and wash it with cold water to remove any remaining impurities.4. Recrystallization: Dissolve the crude 2,4-dichlorobenzoic acid in a suitable solvent, such as hot ethanol or a mixture of ethanol and water, and then allow it to cool slowly. The 2,4-dichlorobenzoic acid will crystallize as it cools, leaving impurities in the solvent.5. Filtration: Filter the recrystallized 2,4-dichlorobenzoic acid and allow it to dry.The final yield of purified 2,4-dichlorobenzoic acid will depend on the efficiency of the isolation and purification steps, but it is generally in the range of 60-80% based on the starting benzoic acid.