Disclosed is a process for the manufacture of haloalkane compounds, and more particularly, to an improved process for the manufacture of the compound 1,1,1,3,3-pentachloropropane (HCC-240fa), which mitigates the formation of by-products. The present invention is also useful in the manufacture of other haloalkane compounds such as HCC-250 and HCC-360. One embodiment of the process comprises a method and system for avoiding the formation of polyvinyl chloride during the production of HCC-240fa from CC14, in which vinyl chloride (VCM) is fed into a reactor as a vapor instead of as a liquid, using a diffusing device to further increase the contact surface between VCM vapor and CC14.