The Friedel-Crafts acylation reaction involves the formation of an acyl chloride and subsequent electrophilic aromatic substitution. However, the reaction you described is not a Friedel-Crafts acylation but rather a chlorination reaction of benzoic acid to form 2,4-dichlorobenzoic acid.To prepare 2,4-dichlorobenzoic acid from benzoic acid and chlorine gas, you can use a Lewis acid catalyst such as aluminum chloride AlCl3 or ferric chloride FeCl3 . The optimum temperature for this reaction is typically around 40-60C. The reaction can be carried out at atmospheric pressure.The yield of the reaction will depend on various factors such as the molar ratio of the reactants, the efficiency of the catalyst, and the reaction time. In general, the yield of 2,4-dichlorobenzoic acid from benzoic acid and chlorine gas can range from 60-80% under optimized conditions.