Pyrolysis reactions involving carbon–halogen bonds

Egger, Kurt W.; Cocks, Alan T.

doi:10.1002/9780470771280.ch10

Cited by 11 publications

(10 citation statements)

References 170 publications

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“…Further, work of these authors [7], they have reconsidered the mechanism of alkyl halide pyrolysis as a very polar TS in terms of an intimate ion-pair intermediate (3) with the presentation of several evidences in support of this idea. However, prior to these mechanistics considerations, Benson and Bose [8] have postulated a semi-ion pair TS mechanism as depicted in (4). Few years later, Benson and O'Neal [9], using model (4), have shown in the calculation of energies and entropies of activation to be in good agreement with the experimental values for their four-membered cyclic TS reaction.…”

mentioning

confidence: 88%

“…However, prior to these mechanistics considerations, Benson and Bose [8] have postulated a semi-ion pair TS mechanism as depicted in (4). Few years later, Benson and O'Neal [9], using model (4), have shown in the calculation of energies and entropies of activation to be in good agreement with the experimental values for their four-membered cyclic TS reaction.…”

mentioning

confidence: 88%

“…Both C 2 and C 4 show decrease in electron density in the TS; C 2 becoming less negatively charged and C 4 becoming positively charged in the TS. Charges in C 3 are very small.…”

Section: Nbo Chargesmentioning

confidence: 99%

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The reaction mechanism of the gas‐phase thermal decomposition kinetics of neopentyl halides: A DFT study

Mora

Márquez

Lezama

et al. 2011

Int J of Quantum Chemistry

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ABSTRACT:The kinetics and mechanisms of the gas-phase elimination reactions of neopentyl chloride and neopentyl bromide have been studied by means of electronic structure calculations using density functional methods: /6-31þþG(d,p). The reaction channels that account in products formation have a common first step involving a Wagner-Meerwein rearrangement. The migration of the halide from the terminal carbon to the more substituted carbon is followed by beta-elimination of HCl or HBr to give two olefins: the Sayzeff and Hoffmann products. Theoretical calculations demonstrated that these eliminations proceed through concerted asynchronous process. The transition state (TS) located for the rate-determining step shows the halide detached and bridging between the terminal carbon and the quaternary carbon, while the methyl group is also migrating in a concerted fashion. The TS is described as an intimate ion-pair with a large negative charge at the halide atom. The concerted migration of methyl group provides stabilization of the TS by delocalizing the electron density between the terminal carbon and the quaternary carbon. The B3LYP/6-31þþG(d,p) allows to obtain reasonable energies and enthalpies of activation. The nature of these reactions is examined in terms of geometrical parameters, electron distribution, and bond order analysis.

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confidence: 88%

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confidence: 88%

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The reaction mechanism of the gas‐phase thermal decomposition kinetics of neopentyl halides: A DFT study

Mora

Márquez

Lezama

et al. 2011

Int J of Quantum Chemistry

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“…A further observation is the similarity of the sensitized and unsensitized $ values; the former is 80% of the latter when high energy triplet donors are used, which suggests that these two reaction routes may have some common intermediate states. Another important point to emerge from these results is the fact that the input of 65 kcal mol-' (ET of 6) is sufficient to cleave effectively C-Cl, C-Br, and C-I bonds of Dc-, 95,81, and 64 kcal mol-I respectively (20). This rules out a simple homolysis mechanism, at least in the cases of the chloro-and bromo-compounds and shows the presence of some factor which provides a much lower energy path for cyclization.…”

Section: Adtiitirjes Inclucling Energy-transfer Agentsmentioning

confidence: 96%

Photocyclization of aryl halides. Part I. 5-(2-Halogenophenyl)-1,3-diphenylpyrazoles; homolytic fission assisted by radical complexation

Grimshaw¹,

Silva²

1980

Can. J. Chem.

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Can. J. Chem. 58, 1880(1980). The photocyclization of 5-(2-halogenopheny1)-1,3-diphenyl pyrazoles proceeds efficiently with the exclusion ofsolvent participation hydrogen abstraction reactions. In agiven solvent, the quantum yields of cyclization (4) of CI, Br, and I compounds show no correlation with carbon-halogen bond dissociation energies. In a series of solvents, 4 varies smoothly with solvent viscosity and is independent of solvent polarity. The 4 values are independent of triplet quenchers, air, intensity and wavelength of radiation, and reactant concentration. Photocyclization can be triplet sensitized at up to 80% of the direct reaction rate and the reactant triplet energies are about 65 kcal mol-I while DC-Br is 81 and DcPcl is 95 kcal mol-'. A mechanism of homolytic fission assisted by radical complexation is proposed to accommodate the results. Photocyclization of the H-and MeO-substituted analogues proceeds inefficiently and with 4 values dependent on solvent polarity. An electrocyclic mechanism is followed in these cases. The assisted homolysis model explains several anomalies in the field of aryl halide photochemistry. [Traduit par lejournal]

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“…These results show that the pyrolysis of PCP and some organic compounds in the soil occurred. One possible explanation for the pyrolysis of PCP involves the cleavage of the Ph Cl bond (95 kcal/mol), which occurs due to its weaker dissociation energy bond in comparison to Ph H (110 kcal/mol) [42], yielding the aromatic radicals. These free phenyl radicals may further decompose into smaller alkyl radicals to form volatile compounds or combine with other phenyl radicals to form large molecules, such as PAHs and biphenyl compounds.…”

Section: Analysis Of the Impact Of Temperature On The Fate Of Pcp Durmentioning

confidence: 99%

Investigation of the degradation of pentachlorophenol in sandy soil via low-temperature pyrolysis

Thuan

Chang

2012

Journal of Hazardous Materials

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Pyrolysis reactions involving carbon–halogen bonds

Cited by 11 publications

References 170 publications

The reaction mechanism of the gas‐phase thermal decomposition kinetics of neopentyl halides: A DFT study

The reaction mechanism of the gas‐phase thermal decomposition kinetics of neopentyl halides: A DFT study

Photocyclization of aryl halides. Part I. 5-(2-Halogenophenyl)-1,3-diphenylpyrazoles; homolytic fission assisted by radical complexation

Investigation of the degradation of pentachlorophenol in sandy soil via low-temperature pyrolysis

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