Kinetic study of the thermolysis of anisole in a hydrogen atmosphere

Arends, Isabel W. C. E.; Louw, R.; Mulder, Peter

doi:10.1021/j100132a020

Cited by 99 publications

(90 citation statements)

References 7 publications

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“…The effect of toluene was discussed in terms of the radical mechanism in the previous works. 6,9 All of our main products, benzene, phenol, and methane except for carbon monoxide were also reported in Ref. 9, whereas only phenol and methane were identified in Ref.…”

mentioning

confidence: 61%

“…A full set of these products were reported along with some other ring compounds in several papers. 1,7,9,11 The presence of phenol as one of the ring products, which is a clear indication of the retention of the CO bond between the phenyl carbon and the oxygen, was reported in all of the papers 1,612 except for an MS (mass spectroscopy) study of anisole pyrolysis. 5 This earliest work at a very high temperature of 950°C referred to the possibility of formation and decomposition of phenoxy to carbon monoxide.…”

Section: Resultsmentioning

confidence: 92%

“…The E a value obtained from the wide temperature range is in reasonable agreement with those reported in the narrower temperature range. 6,7,9 As seen in Figure 8, however, one paper 8 reports a considerably smaller E a value. 25 Thus the anisole pyrolysis reaction discussed here is essentially the same as that so far studied.…”

Section: ¹1mentioning

confidence: 83%

“…1,69,12 Methane was found in most of the papers. 1,6,7,9,11,12 In several papers, 1,7,911 benzene was found as the ring product, always accompanied by phenol and carbon monoxide. All of the information on the product distribution implies the phenyl ring retention and is not contradictory to the bimolecular proton-transfer step (eq 2) followed by the unimolecular proton-transfer step (eq 1).…”

Section: Resultsmentioning

confidence: 99%

“…The 13 C, 2 H, and 1 H NMR spectroscopic study on the toluene-d 5 system clearly indicates that the minor product, bibenzyl is generated not from anisole but from the highconcentration supercritical solvation shell itself, 21 contrary to the phenoxy-radical mechanism. 6,9 Furthermore, when benzene-d 6 or toluene-d 5 is added to anisole to change the molecular environment no propagation products of methyl and hydrogen radicals assumed in the literature are detected. In other words, no 1 H-methylsubstituted derivatives of the deuterated solvents are detected.…”

mentioning

confidence: 89%

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Pathways and Kinetics of Anisole Pyrolysis Studied by NMR and Selective 13C Labeling. Heterolytic Carbon Monoxide Generation

Tsujino¹,

Yasaka²,

Matubayasi³

et al. 2011

Bulletin of the Chemical Society of Japan

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It is important to investigate the kinetics and mechanisms of the thermal reaction process of ethers in order to understand more deeply high-temperature reactions and to develop more efficient high-temperature cracking and processing of fossil (oil and coal) and biomass fuels. In the previous letter, 1 we reported a kinetic study on the noncatalytic pyrolysis of the asymmetric ether, anisole (methyl phenyl ether), at 1 M and at 400430°C. By the product analysis with the gas-and liquid-phase NMR we have succeeded in revealing that the thermal fragmentation of the ether is induced by not homolytic (radical) but heterolytic (ionic) CH bond fission, and that the reaction consists of the slow and the fast elementary steps: (1) The slow step is the unimolecular CH bond fission that is initiated by the intramolecular proton transfer from the methyl to the phenyl group to generate the reactive intermediate formaldehyde (HCHO*). (2) The fast step is composed of the successive intermolecular proton and hydride transfers over the electronegative oxygen atom from the thermally excited intermediate HCHO*, respectively, to the phenoxy and methyl groups of the parent anisole molecule. They are expressed as:C 6 H 5 OCH 3 ! C 6 H 6 þ HCHO Ã ðslowÞ ð 1ÞAs represented here, the major products of the high-pressure (concentration) pyrolysis are benzene, phenol, methane, and carbon monoxide, all in almost equal amounts. The intramolecular proton transfer induced by the COC bending mode was also observed for acetaldehyde, 2 and dimethyl and diethyl ethers; This is called "hinge reaction" at high temperature. 3,4When the elementary steps assumed previously (see below) were the case, CO carbon should come from the methoxy but not from the phenoxy. To test this, here we have selectively labeled the asymmetric ether, anisole, by 13 C as C 6 H 5 O 13 CH 3 . In all of the earlier papers, 512 the following radical CO pathway was postulated:The homolytic bond breakage is assumed to take place between the ether oxygen (eq 3) and the methyl carbon to generate the methyl and phenoxy radicals, and furthermore, the ring-size reduction is presumed to give rise to CO as in eq 4. The thermal fragmentation of dimethyl ether, which is regarded as the prototype of the "unimolecular reaction," has been believed to have the radical mechanism since the pioneering work by Hinshelwood and co-workers in the 1920s. 13 The methoxy group is a key characteristic of these symmetric and asymmetric ethers, and the reactive intermediate formaldehyde* is expected to be generated for both cases. The asymmetric ether can be a promising candidate to distinguish the reaction pathways for the generated hydrocarbon fragments: benzene and methane for anisole and only methane twins for dimethyl ether. Convincing evidence is wanted to resolve the discrepancy in the mechanism of the fundamental thermal reaction. To this end we have scrutinized the CO generation pathway by applying highresolution NMR spectroscopy to the labeled anisole studied in the dark to carefully avoid the ...

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mentioning

confidence: 61%

Section: Resultsmentioning

confidence: 92%

Section: ¹1mentioning

confidence: 83%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 89%

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Pathways and Kinetics of Anisole Pyrolysis Studied by NMR and Selective 13C Labeling. Heterolytic Carbon Monoxide Generation

Tsujino¹,

Yasaka²,

Matubayasi³

et al. 2011

Bulletin of the Chemical Society of Japan

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Parabenzoquinone pyrolysis and oxidation in a flow reactor

Alzueta

Oliva

Glarborg

1998

Int. J. Chem. Kinet.

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An experimental and theoretical study of the pyrolysis and oxidation of parabenzoquinone has been performed. The experiments were conducted in an isothermal quartz flow reactor at atmospheric pressure in the temperature rangeThe main variables 600-1500 K. considered are temperature, oxygen concentration, and presence of CO. A detailed reaction mechanism for the pyrolysis and oxidation chemistry of parabenzoquinone is proposed, which provides a good description of the experimental results. Both the experimental work and the kinetic mechanism proposed for the pyrolysis and oxidation of parabenzoquinone represent the first systematic study carried out for this important aromatic compound.Our pyrolysis results confirm that the primary dissociation channel for p-benzoquinone leads to CO and a C 5 H 4 O isomer, presumably cyclopentadienone. However, significant formation of CO 2 during the pyrolysis may indicate the existence of a secondary dissociation channel leading to CO 2 and a C 5 H 4 isomer. Under oxidizing conditions, consumption of pbenzoquinone occurs mainly by dissociation at lower temperatures. As the temperature increases interaction of OC 6 H 4 O with the radical pool becomes more significant, occurring primarily through hydrogen abstraction reactions followed by ring opening reactions of the OC 6 H 3 O radical.

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Reactions of Diphenyl Ether with Chlorine and Bromine Atoms Around 750 K – Relevance for Gas-Phase “Dioxin” Formation

Wiater

Louw

1999

Eur. J. Org. Chem.

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The title reactions have been studied to scrutinize rate data recently inferred for the two reverse steps – reaction of phenoxy radicals with chlorobenzene and bromobenzene – which were at variance with commonly accepted model values. Both with chlorine and bromine atoms, splitting to halobenzene and phenoxy radical was found to occur in competition with abstraction of o‐, m‐, p‐hydrogen atoms. On this basis, the displacements of Cl and Br from the benzene ring by phenoxy radicals must have activation energies above 20 kcal/mol, and are therefore slow. As a consequence, formation of “dioxins” from halogenated phenols, in (slow) combustion, should proceed by combination of two (halo)phenoxy radicals rather than by displacement of (ortho‐)halogen in a halophenol molecule.

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Kinetic study of the thermolysis of anisole in a hydrogen atmosphere

Cited by 99 publications

References 7 publications

Pathways and Kinetics of Anisole Pyrolysis Studied by NMR and Selective 13C Labeling. Heterolytic Carbon Monoxide Generation

Pathways and Kinetics of Anisole Pyrolysis Studied by NMR and Selective 13C Labeling. Heterolytic Carbon Monoxide Generation

Parabenzoquinone pyrolysis and oxidation in a flow reactor

Reactions of Diphenyl Ether with Chlorine and Bromine Atoms Around 750 K – Relevance for Gas-Phase “Dioxin” Formation

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