THE HIGH-TEMPERATURE PYROLYSIS OF HEXACHLOROPROPENE - KINETIC-ANALYSIS OF PATHWAYS TO FORMATION OF PERCHLORO-ARYLBENZENES

We present the results of a study of the thermal degradation of hexach loropropene in a tubular flow reactor with in-line GC-MS product analy sis. Hexachloropropene was observed to be thermally fragile with initi al reaction products (T < 773 K) including CCl4, C2Cl4, C2Cl6, and C3C l4, (a). At higher temperatures (up to 1223 K), pronounced molecular g rowth was observed with reaction products including C4Cl6, C6Cl6 (cy), C6Cl8, C8Cl8 (cy), and C12Cl8 (cy). Kinetic modeling of observed prod uct yields indicated that Cl displacement of CCl3 radicals was the dom inant initiation pathway for conversion of C3Cl6 into C2Cl4, CCl4, and C2Cl6. Four reaction submodels were considered in developing a model for the formation of C6Cl6 (cy): recombination of C3Cl5, recombination of C3Cl3, pericyclic addition of C3Cl4 (a), and addition reactions of C-2 and C-4 unsaturated radicals with C2Cl2. Recombination of C3Cl5 r adicals accounted for all of the observed yields at low temperatures ( T < 873 K). At higher temperatures C3Cl3 recombination accounted for a bout 80% of observed yields with C3Cl5 recombination accountable for t he remainder. Purely C-4 radical-molecule reactions were also shown to make significant contributions to formation of octachlorostyrene (C8C l8 (cy)). Consequently, the more conventional C-2 molecular growth pat hways were observed to be insignificant for this system.