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We combine combustion experiments and density functional theory (DFT) calculations to investigate the formation of chlorobenzenes from oxidative thermal decomposition of 1,3-dichloropropene.Mono-to hexa-chlorobenzenes are observed between 800 and 1150 K, and the extent of chlorination was proportional to the combustion temperature. Higher chlorinated congeners of chlorobenzene (tetra-, penta-, hexa-chlorobenzene) are only observed in trace amounts between 950 and 1050 K.DFT calculations indicate that cyclisation of chlorinated hexatrienes proceeds via open-shell radical pathways. These species represent key components in the formation mechanism of chlorinated polyaromatic hydrocarbons. Results presented herein should provide better understanding of the evolution of soot from combustion/pyrolysis of short chlorinated alkenes.

Oxidative decomposition of 1,3-dichloropropene was investigated using quantum chemical molecular dynamics (QM/MD) at 1500 and 3000 K. Thermal oxidation of 1,3-dichloropropene was initiated by (1) abstraction of allylic H/Cl by O2 and (2) intra-annular C-Cl bond scission and elimination of allylic Cl. A kinetic analysis shows that (2) is the more dominant initiation pathway, in agreement with QM/MD results. These QM/MD simulations reveal new routes to the formation of major products (H2O, CO, HCl, CO2), which are propagated primarily by the chloroperoxy (ClO2), OH, and 1,3-dichloropropene derived radicals. In particular, intra-annular C-C/C-H bond dissociation reactions of intermediate aldehydes/ketones are shown to play a dominant role in the formation of CO and CO2. Our simulations demonstrate that both combustion temperature and radical concentration can influence the product yield, however not the combustion mechanism.

PVC pyrolyses in fires eliminating HCl, which can subsequently participate in formation of chloraromatic pollutants. In this study, the density functional theory (DFT) has been deployed to simulate the mechanisms of HCl elimination from pyrolysing PVC. Although PVC consists mainly of polymerised chlorethene, it also contains other structural entities as impurities or defect compounds, which significantly enhance its decomposition. For this reason, we have studied elimination of HCl from seven compounds that represent the defects in PVC. We have found two generic pathways for the elimination of HCl. The first involves a CCl fission at an allylic site and a C-H cleavage at a vinylic site, whereas the second entails scissions of allylic Cl and methylenic H. The latter pathway appears more favourable from thermodynamic and kinetic standpoints. We have investigated the effect of the length of carbon chain on reaction and activation enthalpies by considering analogous dehydrochlorination pathways for short chlorinated alkanes (i.e., C 3 , C 4 ), discovering the reaction and activation enthalpies required for HCl elimination to be independent of the length of the carbon chain. We then explored the effects of temperature and pressure on rate constants for all possible dehydrochlorination pathways within the formalism of the unimolecular reaction rate theory of RRKM. Pressure fall-off regions extend generally between 0.001 and 1.0 atm, and the dehydrochlorination reactions exhibit pressure-independent behaviour even under ambient pressure. Kinetic parameters presented herein should be useful to model the decomposition of PVC in fires.

We present a quantum chemical investigation of benzofuran and cholorobenzofuran formation mechanisms during the combustion of 1,3-dichloropropene. Density functional theory and Gaussian-n thermochemical methods are used to propose detailed mechanistic reaction pathways. These calculations indicate that oxidation of phenylvinyl radical intermediates and subsequent ring closure are key mechanistic pathways in the formation of benzofuran and chlorobenzofuran. Thermochemical and kinetic parameters presented herein will assist in further elucidation of dioxin formation mechanisms from thermolyses of hydrocarbon moieties. V C 2015 Wiley Periodicals, Inc.