A Quantum Mechanical Study on the Formation of PCDD/Fs from 2-Chlorophenol as Precursor

Abstract

The most direct route to the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in combustion and thermal processes is the gas-phase reaction of chemical precursors such as chlorinated phenols. Detailed insight into the mechanism and kinetics properties is a prerequisite for understanding the formation of PCDD/Fs. In this paper, we carried out molecular orbital theory calculations for the homogeneous gas-phase formation of PCDD/Fs from 2-chlorophenol (2-CP). The profiles of the potential energy surface were constructed, and the possible formation pathways are discussed. The single-point energy calculation was carried out at the MPWB1K/ 6-311+G(3f,2p) level. Several energetically favorable formation pathways were revealed for the first time. The rate constants of crucial elementary steps were deduced over a wide temperature range of 600 approximately 1200 K using canonical variational transition-state theory (CVT) with small curvature tunneling contribution (SCT). The rate-temperature formulas were fitted. The ratio of PCDD to PCDF formed shows strong dependency on the reaction temperature and chlorophenoxy radicals (CPRs) concentration.

Homogeneous gas-phase formation of polychlorinated naphthalene from dimerization of 4-chlorophenoxy radicals and cross-condensation of phenoxy radical with 4-chlorophenoxy radical: Mechanism and kinetics study

“…H is calculated at 0 K. which covers the possible formation temperature of PCNs in combustion and thermal processes. Actually, the CVT/SCT method has been successfully performed for the elementary reactions of our previous studies involved in the formation of PCDD/Fs from CP as precursors [27][28][29][30], and it is an efficient method to calculate the rate constants.…”

“…In his scheme, PCNs are formed via carbon-carbon coupling at unchlorinated ortho sites of CPR pairs, resulting in an intermediate chlorinated o,o -dihydroxybiphenyl (chloro-DOHB) [18][19][20]. On the one hand, chloro-DOHB can produce dibenzofuran products via H shift, http tautomerization and loss of H 2 O, which we previously studied [27][28][29][30][31]. On the other hand, chloro-DOHB can form chlorinated dihydrofulvaene by two CO loss and ring closure processes, followed by PCN formation via pathways analogous to the mechanism proposed by Melius [18][19][20]32].…”

Formation of Polychlorinated Dibenzo-p-Dioxins and Polychlorinated Dibenzofurans and Their Precursors in Fires of Pyrethroid Pesticide Alpha-Cypermethrin

“…The recombination of the oxygen-centred 2-chlorophenoxy radical with the carbon (hydrogen) centred radical has been widely documented to form a keto-ether [7,9,10]. Two kinds of oxygen-carbon coupling modes exist, as represented in Fig.…”

“…Unfortunately the present understanding of mechanisms of PCDD/F formation in the combustion of pesticides is quite inadequate, compared to those of chlorinated naphthalenes, diphenyl ether, dibenzofurans, biphenyls, chlorobenzene, chlorophenol and PVC [6][7][8][9][10][11][12][13][14]. While the thermal decomposition of alpha-cypermethrin has been studied, no publication has examined the formation of PCDD/F from this pesticide.…”

Electrosynthesis of blue-light-emitting oligo(1-bromopyrene) with favorable solubility

“…Electric charge (11) 0.115551 C (13) 0.122169 C (15) −0.002373 (12) 0.131134 C (14) 0.127249 Quantum chemical calculations can provide some theoretical information on the chemical structure and property [35][36][37]. For more information on the structure of polymers and the polymerization mechanism, we calculated the atomic electron-density population ( Table 1) and proportion of the frontier orbitals (Scheme 2) of the BrP monomers using the B3LYP/6-31G(d,p) level of Gaussian 03 software.…”