A process for preparing a 1,1,1,2,3-pentachloropropane product comprising: 1-a) providing a reaction mixture comprising ethylene, carbon tetrachloride and a catalyst in a principal alkylation zone to produce 1,1,1,3-tetrachloropropane in the reaction mixture, and 1-b) treating the reaction mixture obtained in step 1-a) by removing ethylene and catalyst to obtain a 1,1,1,3-tetrachloropropane feedstock; 2-a) contacting the 1,1,1,3-tetrachloropropane feedstock with a catalyst in a dehydrochlorination zone to produce a reaction mixture comprising 1,1,1,3-tetrachloropropane and 1,1,3-trichloropropene, and 2-b) treating the reaction mixture obtained in step 2-a) by extracting 1,1,3-trichloropropane to obtain a 1,1,3-trichloropropene feedstock; 3-a) contacting the 1,1,3-trichloropropene feedstock with chlorine in a reaction zone to produce a reaction mixture containing 1,1,1,2,3-pentachloropropane and 1,1,3-trichloropropene, the reaction zone being different from the dehydrochlorination zone, and 3-b) treating the reaction mixture obtained in step 3-a) by extracting to obtain the 1,1,1,2,3-pentachloropropane product, wherein, in step 1-a), the concentration of the 1,1,1,3-tetrachloropropane in the reaction mixture in the principal alkylation zone is maintained at a level such that the molar ratio of 1,1,1,3-tetrachloropropane: carbon tetrachloride in the reaction mixture does not exceed: • 95:5 where the principal alkylation zone is in continuous operation, or • 99:1 where the principal alkylation zone is in batchwise operation; wherein, in step 2-a), the concentration of 1,1,3-trichloropropene in the reaction mixture produced in the dehydrochlorination zone is maintained at a level such that the molar ratio of 1,1,3-trichloropropene: 1,1,1,3-tetrachloropropane does not exceed 30:70; and wherein, in step 3-a), the degree of conversion of the starting 1,1,3-trichloropropene to the resulting 1,1,1,2,3-pentachloropropane is maintained at a level such that the molar ratio of 1,1,1,2,3-pentachloropropane: 1,1,3-trichloropropene does not exceed 95: 5. 1-a) providing a reaction mixture comprising ethylene, carbon tetrachloride and a catalyst in a principal alkylation zone to produce 1,1,1,3-tetrachloropropane in the reaction mixture, and 1-b) treating the reaction mixture obtained in step 1-a) by removing ethylene and catalyst to obtain a 1,1,1,3-tetrachloropropane feedstock; 2-a) contacting the 1,1,1,3-tetrachloropropane feedstock with a catalyst in a dehydrochlorination zone to produce a reaction mixture comprising 1,1,1,3-tetrachloropropane and 1,1,3-trichloropropene, and 2-b) treating the reaction mixture obtained in step 2-a) by extracting 1,1,3-trichloropropane to obtain a 1,1,3-trichloropropene feedstock; 3-a) contacting the 1,1,3-trichloropropene feedstock with chlorine in a reaction zone to produce a reaction mixture containing 1,1,1,2,3-pentachloropropane and 1,1,3-trichloropropene, the reaction zone being different from the dehydrochlorination zone, and 3-b) treating the reaction mixture obtained in step 3-a) by extracting to obtain the 1,1,1,2,3-pentachloropropane product, wherein, in step 1-a), the concentration of the 1,1,1,3-tetrachloropropane in the reaction mixture in the principal alkylation zone is maintained at a level such that the molar ratio of 1,1,1,3-tetrachloropropane: carbon tetrachloride in the reaction mixture does not exceed: • 95:5 where the principal alkylation zone is in continuous operation, or • 99:1 where the principal alkylation zone is in batchwise operation; • 95:5 where the principal alkylation zone is in continuous operation, or • 99:1 where the principal alkylation zone is in batchwise operation; wherein, in step 2-a), the concentration of 1,1,3-trichloropropene in the reaction mixture produced in the dehydrochlorination zone is maintained at a level such that the molar ratio of 1,1,3-trichloropropene: 1,1,1,3-tetrachloropropane does not exceed 30:70; and wherein, in step 3-a), the degree of conversion of the starting 1,1,3-trichloropropene to the resulting 1,1,1,2,3-pentachloropropane is maintained at a level such that the molar ratio of 1,1,1,2,3-pentachloropropane: 1,1,3-trichloropropene does not exceed 95: 5.