Kinetic Properties for the Complete Series Reactions of Chlorophenols with OH Radicals—Relevance for Dioxin Formation

Abstract

The chlorophenoxy radical (CPR) is a key intermediate species in the formation of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). In municipal waste incinerators, the reactions of chlorophenols with OH radicals play the most central role in the formation of chlorophenoxy radicals. In this paper, molecular orbital theory calculations have been performed to investigate the formation of chlorophenoxy radicals from the complete series reactions of 19 chlorophenol congeners with OH radicals. The single-point energy calculation was carried out at the MPWB1K/6-311+G(3df,2p) level on the basis of the MPWB1K/6-31+G(d,p) optimized geometries. The kinetic modeling of the PCDD/PCDF (PCDD/F for short) formation demands the knowledge of the rate parameters for the formation of chlorophenoxy radicals from chlorophenols. So, the kinetic properties of the reactions of chlorophenols with OH radicals were deduced over a wide temperature range of 600-1200 K using canonical variational transition-state theory (CVT) with small curvature tunneling contribution (SCT). This study shows that the chlorine substitution at the ortho position in chlorophenol not only has a significant effect on the structures of chlorophenols, prereactive intermediates, the transition states, and chlorophenoxy radicals, but also plays a decisive role in determining the rate parameters.

Formation of dibenzofuran, dibenzo-p-dioxin and their hydroxylated derivatives from catechol

“…13,14,16,25 We find that the presence of two OH substituents at ortho positions does not influence this high ) and lead to the formation of preDF structures. To the best of our knowledge, our discussed C-C ring-closure reactions have never been proposed as pathways for the formation of substituted DF molecules.…”

Influence of water on the homogeneous gas-phase formation mechanism of polyhalogenated dioxins/furans from chlorinated/brominated phenols as precursors

“…2-CP + OH (Gao et al, 2013). In the non-hydrated intermediates, only one hydrogen bond is formed between the phenoxylhydrogen atom of HP and the oxygen atom of OH radical (Xu et al, 2010). However, with the addition of a water molecule, a six-center cyclic structure is formed through two hydrogen bonds, one is the hydrogen of the OH radical binding to the oxygen of the water, another is a hydrogen atom of the water binding to the phenoxyl-oxygen of HP.…”

“…In the previously published papers, we have investigated the homogeneous gas-phase formation of PCDD/Fs from CPs as precursors as well as the homogeneous gas-phase formation of PBDD/Fs from BPs as precursors (Zhang et al, 2008(Zhang et al, , 2009Yu et al, 2011;Xu et al, 2010;Gao et al, 2013). Based on these studies, the present work focuses on the influence of water on the homogeneous gas-phase formation mechanism of polyhalogenated dibenzo-p-dioxin/benzofurans (PHDD/Fs, including PCDD/Fs and PBDD/Fs) from halogenated phenols (HPs, including CPs and BPs) with the aid of quantum chemical calculations.…”

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.…”