Fire Safety Science Digital Archive

Fires provide optimum conditions to produce polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F) as well as polychlorinated biphenyls (PCB). In this study, we deploy the density functional theory (DFT) to simulate the production of PCB, and polychlorinated dibenzofurans (PCDF), which are formed in fires from the precursor chlorobenzene in preference to polychlorinated dibenzo-p-dioxins (PCDD). We demonstrate that, combinations of chlorobenzene with chlorophenyl radicals generate PCB compounds through an exothermic reaction of 18.7 kcal/mol. H on the pivot bond could be self-expulsed through an energy barrier of 21.7 kcal/mol to produce 2,2'-dichlorobiphenyl. Combinations of chlorobenzene and chlorophenoxy radicals, formed in early stages of the oxidation of chlorobenzene, afford 16 different precursors for PCDFs. All these reactions are endothermic, between 18.3 to 38.8 kcal/mol at 298 K, with activation enthalpies higher by 3-10 kcal/mol than the reaction enthalpies.