The products of the thermal decomposition of CH3CHO

Vasiliou, AnGayle K.; Piech, Krzysztof; Zhang, Xu; Nimlos, Mark R.; Ahmed, Musahid; Golan, Amir; Kostko, Oleg; Osborn, David L.; Daily, John W.; Stanton, John F.; Ellison, G. Barney

doi:10.1063/1.3604005

Cited by 46 publications

(89 citation statements)

References 40 publications

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“…Our preliminary analysis 18 reaffirmed the conclusions reported in our laboratory 14,16 that the thermal decomposition of CH 3 CHO involves a dominant contribution from (R1) and a minor contribution from (R2). These simulations 18 also indicated that a minor amount of CH 2 CHOH is formed in most high temperature systems, observations consistent with subsequent experiments by Vasiliou et al 19 The present study expands on the preliminary analysis 18 15,19 The present simulations highlight that keto-enol tautomerization of CH 3 CHO to CH 2 CHOH is an important process 6 at high temperatures. Furthermore, bimolecular reactions of these two species with atoms and radicals are essential to explain the unique product spectra from the micro-tubular studies.…”

Section: Introductionsupporting

confidence: 88%

“…With the aid of high-level electronic structure calculations, theoretical kinetics predictions 16 were in quantitative agreement with experiment and indicated that the H-atom yield was only due to C-C bond fission (R1) and the non H-atom yield corresponded to the formation of CH 4 and CO primarily due to the "roaming" mechanism. However, recent pyrolysis studies on hydrogenated and 5 deuterated acetaldehyde in a micro-tubular reactor by Vasiliou et al 15 question the validity of the proposed "roaming" mechanism because CH 4 was not detected in these experiments. Vasiliou et al 15 recently observed the formation of CH 3 15 since these molecules had not been observed in any of the previous CH 3 CHO thermal decomposition experiments 2,4,5,8,9,12 that sampled products and intermediates over substantial ranges of temperature and pressure.…”

Section: Introductionmentioning

confidence: 94%

“…13 2. Recent experimental 14,15 and theoretical 16 studies have suggested new mechanistic thermal decomposition pathways not considered in prior literature studies.…”

Section: Introductionmentioning

confidence: 99%

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Resolving Some Paradoxes in the Thermal Decomposition Mechanism of Acetaldehyde

et al. 2015

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The mechanism for the thermal decomposition of acetaldehyde has been revisited with an analysis of literature kinetics experiments using theoretical kinetics. The present modeling study was motivated by recent observations, with very sensitive diagnostics, of some unexpected products in high temperature microtubular reactor experiments on the thermal decomposition of CH3CHO and its deuterated analogs, CH3CDO, CD3CHO, and CD3CDO. The observations of these products prompted the authors of these studies to suggest that the enol tautomer, CH2CHOH (vinyl alcohol), is a primary intermediate in the thermal decomposition of acetaldehyde. The present modeling efforts on acetaldehyde decomposition incorporate a master equation reanalysis of the CH3CHO potential energy surface (PES). The lowest-energy process on this PES is an isomerization of CH3CHO to CH2CHOH. However, the subsequent product channels for CH2CHOH are substantially higher in energy, and the only unimolecular process that can be thermally accessed is a reisomerization to CH3CHO. The incorporation of these new theoretical kinetics predictions into models for selected literature experiments on CH3CHO thermal decomposition confirms our earlier experiment and theory-based conclusions that the dominant decomposition process in CH3CHO at high temperatures is C-C bond fission with a minor contribution (∼10-20%) from the roaming mechanism to form CH4 and CO. The present modeling efforts also incorporate a master-equation analysis of the H + CH2CHOH potential energy surface. This bimolecular reaction is the primary mechanism for removal of CH2CHOH, which can accumulate to minor amounts at high temperatures, T > 1000 K, in most lab-scale experiments that use large initial concentrations of CH3CHO. Our modeling efforts indicate that the observation of ketene, water, and acetylene in the recent microtubular experiments are primarily due to bimolecular reactions of CH3CHO and CH2CHOH with H-atoms and have no bearing on the unimolecular decomposition mechanism of CH3CHO. The present simulations also indicate that experiments using these microtubular reactors when interpreted with the aid of high-level theoretical calculations and kinetics modeling can offer insights into the chemistry of elusive intermediates in the high-temperature pyrolysis of organic molecules.

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Section: Introductionsupporting

confidence: 88%

Section: Introductionmentioning

confidence: 94%

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Resolving Some Paradoxes in the Thermal Decomposition Mechanism of Acetaldehyde

et al. 2015

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“…Similar experiments on the pyrolysis of acetaldehyde 34,40 show that it can also dissociate to form ketene + H 2 or acetylene + water, via bimolecular reactions of the starting material with hydrogen atoms. It is difficult to determine whether the secondary reaction of ethylene oxide leading to ketene is actually occurring because ketene is also a product in Reaction 1.…”

Section: Articlementioning

confidence: 75%

Pyrolysis Reactions of 3-Oxetanone

et al. 2015

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The pyrolysis products of gas-phase 3-oxetanone were identified via matrix-isolation Fourier transform infrared spectroscopy and photoionization mass spectrometry. Pyrolysis was conducted in a hyperthermal nozzle at temperatures from 100 to 1200 °C with the dissociation onset observed at ∼600 °C. The ring strain in the cyclic structure of 3-oxetanone causes the molecule to decompose at relatively low temperatures. Previously, only one dissociation channel, producing formaldehyde and ketene, was considered as significant in photolysis. This study presents the first experimental measurements of the thermal decomposition of 3-oxetanone demonstrating an additional dissociation channel that forms ethylene oxide and carbon monoxide. Major products include formaldehyde, ketene, carbon monoxide, ethylene oxide, ethylene, and methyl radical. The first four products stem from initial decomposition of 3-oxetanone, while the additional products, ethylene and methyl radical, are believed to be due to further reactions involving ethylene oxide.

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“…11,13 In brief, gas mixtures (0.25% cyclohexanone in argon) are pulsed (Parker General Valve) into the hot microreactor at 10 Hz. Products from the microreactor are directed toward a cold CsI window where they are frozen into an argon matrix and subsequently analyzed by IR absorption spectroscopy.…”

Section: Matrix Isolation Infrared Spectroscopymentioning

confidence: 99%

Isomerization and Fragmentation of Cyclohexanone in a Heated Micro-Reactor

Ellison¹,

Daily²,

Stanton³

et al. 2016

Proceedings of the 71st International Symposium on Molecular Spectroscopy

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ABSTRACT:The thermal decomposition of cyclohexanone (C 6 H 10 O) has been studied in a set of flash-pyrolysis microreactors. Decomposition of the ketone was observed when dilute samples of C 6 H 10 O were heated to 1200 K in a continuous flow microreactor. Pyrolysis products were detected and identified by tunable VUV photoionization mass spectroscopy and by photoionization appearance thresholds. Complementary product identification was provided by matrix infrared absorption spectroscopy. Pyrolysis pressures were roughly 100 Torr, and contact times with the microreactors were roughly 100 μs. Thermal cracking of cyclohexanone appeared to result from a variety of competing pathways, all of which open roughly simultaneously. Isomerization of cyclohexanone to the enol, cyclohexen-1-ol (C 6 H 9 OH), is followed by retroDiels−Alder cleavage to CH 2 CH 2 and CH 2 C(OH)−CHCH 2 . Further isomerization of CH 2 C(OH)−CHCH 2 to methyl vinyl ketone (CH 3 CO−CHCH 2 , MVK) was also observed. Photoionization spectra identified both enols, C 6 H 9 OH and CH 2 C(OH)−CH CH 2 , and the ionization threshold of C 6 H 9 OH was measured to be 8.2 ± 0.1 eV. Coupled cluster electronic structure calculations were used to establish the energetics of MVK. The heats of formation of MVK and its enol were calculated to be Δ f H 298 (cis-CH 3 CO−CHCH 2 ) = −26.1 ± 0.5 kcal mol −1 and Δ f H 298 (s-cis-1-CH 2 C(OH)−CHCH 2 ) = −13.7 ± 0.5 kcal mol −1. The reaction enthalpy Δ rxn H 298 (C 6 H 10 O → CH 2 CH 2 + s-cis-1-CH 2 C(OH)−CHCH 2 ) is 53 ± 1 kcal mol −1 and Δ rxn H 298 (C 6 H 10 O → CH 2 CH 2 + cis-CH 3 CO−CHCH 2 ) is 41 ± 1 kcal mol −1 . At 1200 K, the products of cyclohexanone pyrolysis were found to be C 6 H 9 OH, CH 2 C(OH)−CHCH

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The products of the thermal decomposition of CH3CHO

Cited by 46 publications

References 40 publications

Resolving Some Paradoxes in the Thermal Decomposition Mechanism of Acetaldehyde

Resolving Some Paradoxes in the Thermal Decomposition Mechanism of Acetaldehyde

Pyrolysis Reactions of 3-Oxetanone

Isomerization and Fragmentation of Cyclohexanone in a Heated Micro-Reactor

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