Disclosed is a process for preparing a highly pure 1,1,1,2,3-pentachloropropane product. The method comprises 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; 1-b) treating the reaction mixture obtained in step 1-a) 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; 2-b) treating the reaction mixture obtained in step 2-a) 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) to obtain the highly pure 1,1,1,2,3-pentachloropropane product.