Mechanistic studies on the dibenzofuran and dibenzo‑p‑dioxin formation reactions from anthracene.

Polychlorinated dibenzo‑p‑dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are highly toxic, carcinogenic and mutagenic to humans. As precursors of PCDD/Fs, dibenzofuran (DF) and dibenzo‑p‑dioxin (DD) have received considerable public and scientific attention. To reduce the emission of PCDD/Fs, it is critical to explore the formation mechanisms of DF and DD. The present study delineated the DF and DD formation mechanisms from anthracene partial oxidation with the aid of high-accuracy quantum chemistry calculations. The rate constants of crucial elementary steps were obtained utilizing canonical variational transition-state (CVT) theory with the small curvature tunneling (SCT) correction. The results indicate that anthracene could be important precursor of DF and DD, because of the potential barriers for all the major elementary reactions are lower than 33.54kcalmol-1. This work also reveals that water molecule plays an important catalytic effect during the formation of both DF and DD by lowering the barriers of about 27.24kcalmol-1. For the water-assisted formation pathway, DF is the dominate product of anthracene partial oxidation with the highest barrier of 30.45kcalmol-1. For the non-water-assisted formation pathway, DD is the dominate product with the highest barrier of 33.54kcalmol-1.