Formation of Trichlorinated Dibenzo‐<i>p</i>‐dioxins from 2,4‐Dichlorophenol and 2,4,5‐Trichlorophenolate: A Theoretical Study

Suárez, Ernesto; Suárez, Dimas; Menéndez, María Isabel Menéndez; López, Raḿon; Sordo, T. L.

doi:10.1002/cphc.200600355

Cited by 6 publications

(3 citation statements)

References 64 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The formation mechanisms of PCDD/Fs have been extensively studied both experimentally − and theoretically − in the past three decades. It has been well established that PCDD/Fs are formed through two general catalytic processes: the de novo route and the precursor route.…”

Section: Introductionmentioning

confidence: 99%

New Insight into the Formation Mechanism of PCDD/Fs from 2-Chlorophenol Precursor

Pan¹,

Zhang²,

Han³

et al. 2013

Environ. Sci. Technol.

View full text Add to dashboard Cite

Chlorophenols are known as precursors of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). The widely accepted formation mechanism of PCDD/Fs always assumes chlorophenoxy radicals as key and important intermediates. Based on the results of density functional theory calculations, the present work reports new insight into the formation mechanism of PCDD/Fs from chlorophenol precursors. Using 2-chlorophenol as a model compound of chlorophenols, we find that apart from the chlorinated phenoxy radical, the chlorinated phenyl radical and the chlorinated α-ketocarbene also have great potential for PCDD/F formation, which has scarcely been considered in previous literature. The calculations on the self- and cross-coupling reactions of the chlorophenoxy radical, the chlorinated phenyl radical and the chlorinated α-ketocarbene show that the formations of 1-MCDD, 1,6-DCDD, 4,6-DCDF, and 4-MCDF are both thermodynamically and kinetically favorable. In particular, some pathways involving the chlorinated phenyl radicals and the chlorinated α-ketocarbene are even energetically more favorable than those involving the chlorophenoxy radical. The calculated results may improve our understanding for the formation mechanism of PCDD/Fs from chlorophenol precursors and be informative to environmental scientists.

show abstract

Section: Introductionmentioning

confidence: 99%

New Insight into the Formation Mechanism of PCDD/Fs from 2-Chlorophenol Precursor

Pan¹,

Zhang²,

Han³

et al. 2013

Environ. Sci. Technol.

View full text Add to dashboard Cite

show abstract

“…Experimental evidence generally points to a two‐step process, which is dependent upon nucleophile, leaving group, and the presence of electron‐withdrawing substituents . In contrast, ab initio and semiempirical theoretical treatments reveal both two‐step and single‐step mechanisms …”

Section: Introductionmentioning

confidence: 99%

Nucleophilic aromatic substitution in chlorinated aromatic systems with a glutathione thiolate model

Boerth

Arvanites

2016

J. Phys. Org. Chem.

View full text Add to dashboard Cite

The conjugation of glutathione with chlorobenzene and di‐, tri‐, tetra‐, and hexa‐chlorinated benzenes via nucleophilic aromatic substitution was modeled for isolated reacting species by ab initio molecular orbital theory to provide an understanding of the intrinsic reactivity of unactivated chloroaromatic systems. Computations at the HF/6‐31+G(d,p) level were augmented with electron correlation corrections using MP2 theory and density functional theory at the B3LYP level. Features of the reaction hypersurface were elaborated using thiolate (thiomethoxide) as the model for an enzyme‐activated glutathione molecule. Unlike the similar reaction with 1‐chloro‐2, 4‐dinitrobenzene a known substrate with glutathione, no σ‐complex or Meisenheimer complex was isolated as a true intermediate on the hypersurface. Instead, the σ‐complex appears as a transition state, preceded and followed by two ion‐molecule complexes in which the approaching and departing anions reside in the plane of the aromatic ring. Solvent calculations show a very similar hypersurface landscape with only one transition state and no intermediate. Activation energies are somewhat greater than for 1‐chloro‐2, 4‐dinitrobenzene owing to the lack of nitro substituents, which provide stabilization in these systems. Nevertheless, activation energies calculated at correlated levels indicate that these reactions are still feasible and consistent with experiment. Transition states and activation energies for dichlorobenzenes and polychlorobenzenes are lower in energy than for chlorobenzene implying greater stability conferred to the transition state by ortho and para substituents.

show abstract

“…PCDD/Fs are formed as unwanted byproducts in various combustion processes, especially the thermal treatment of municipal waste. In the past three decades, the formation mechanisms of PCDD/PCDFs (PCDD/Fs for short) have been extensively studied both experimentally − and theoretically. − It has been well established that chlorophenols (CPs) are the predominant and direct precursors of PCDD/Fs under pyrolytic or oxidative conditions in thermal systems. CPs can be found ubiquitously in the environment due to their extensive and long-term use in industry and in daily life. , It is widely accepted that the formation of chlorophenoxy radicals (CPRs) via two general pathways (homogeneous gas-phase reactions and heterogeneous surface-catalyzed processes) is the initial and key step in the formation of PCDD/Fs from CPs. − So previous studies by Zhang et al ,, and other groups ,− exclusively emphasized the importance of dimerization of CPRs, − although, in an early work, Lomnicki et al proposed the formation of PCDD/Fs through condensation of the phenoxyl diradical (also called α-ketocarbene).…”

Section: Introductionmentioning

confidence: 99%

New Understanding of the Formation of PCDD/Fs from Chlorophenol Precursors: A Mechanistic and Kinetic Study

Zhang

Gao

et al. 2014

J. Phys. Chem. A

View full text Add to dashboard Cite

Although chlorophenols (CPs) are considered to be the most important and direct precursors of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), our understanding of the formation mechanism of PCDD/Fs is exclusively limited to an invariable idea that chlorophenoxy radicals (CPRs) are only necessary intermediates. The present work presents a systematic theoretical study that aims at providing new insight into the homogeneous formation of PCDD/Fs from CPs. Two different types of radicals from CPRs, i.e., substituted phenyl radicals and phenoxyl diradicals, are proposed to serve as potential sources contributing to the formation of PCDD/Fs. The thermodynamic and kinetic properties of reactions of 2-chlorophenol (2-CP), as a representative of CP congeners, with atomic H to produce various potential radicals forming PCDD/Fs are studied by performing density functional theory calculations and direct kinetics studies. The newly proposed radicals, especially substituted phenoxyl diradicals (the most direct intermediates of PCDD/Fs), can be formed via reactions of 2-CP with atomic H with small barriers and large reaction energies. They should be expected to be responsible for the homogeneous formation of PCDD/Fs under high temperature. Several typical PCDD/F products are predicated through direct self- and cross-couplings of the newly proposed radicals. The radical coupling patterns proposed in the present work expand our understanding of the formation mechanism of PCDD/Fs from CP precursors.

show abstract

Formation of Trichlorinated Dibenzo‐p‐dioxins from 2,4‐Dichlorophenol and 2,4,5‐Trichlorophenolate: A Theoretical Study

Cited by 6 publications

References 64 publications

New Insight into the Formation Mechanism of PCDD/Fs from 2-Chlorophenol Precursor

New Insight into the Formation Mechanism of PCDD/Fs from 2-Chlorophenol Precursor

Nucleophilic aromatic substitution in chlorinated aromatic systems with a glutathione thiolate model

New Understanding of the Formation of PCDD/Fs from Chlorophenol Precursors: A Mechanistic and Kinetic Study

Contact Info

Product

Resources

About