Probing O2-dependence of tetrahydrofuranyl reactions via isomer-resolved speciation

Koritzke, Alanna L.; Dewey, Nicholas S.; Christianson, Matthew G.; Hartness, Samuel W.; Doner, Anna C.; Webb, Annabelle R.; Rotavera, Brandon

doi:10.1016/j.combustflame.2023.112640

Cited by 5 publications

(5 citation statements)

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“…Similar to alkyl radicals, cyclic ethers also undergo complex reactions with O 2 ( 39 – 41 ). In addition to unimolecular reactions, however, RO 2 radicals can undergo bimolecular reactions including with other RO 2 radicals ( 42 ). Figure 2 depicts, as an example, a set of reactions of 2-methyltetrahydrofuran that produce highly oxidized, multifunctional intermediates in sequential steps mediated by organic hydroperoxides (ROOH), which result in species of decreased volatility that can partition to the particle phase and contribute to OxyPOA formation.…”

Section: Resultsmentioning

confidence: 99%

“…Subsequent H-abstraction and O 2 -addition produces cyclic ether peroxy radicals (RO 2 ), such as 2-methyl-tetrahydrofuranyl-3-peroxy, which can undergo additional QOOH-mediated reactions or act as a hydrogen abstractor to produce ROOH. Abstraction of tertiary hydrogen from ROOH and barrierless O─O scission of the resultant carbon-centered radical, carbonyl-substituted species are produced coincident with OH in a chain-propagating step ( 42 ). Subsequent oxidation of species such as 2-methyl-tetrahydrofuran-3-one yields condensable species that form OxyPOA.…”

Section: Resultsmentioning

confidence: 99%

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Alkylperoxy radicals are responsible for the formation of oxygenated primary organic aerosol

El Hajj,

Hartness,

Vandergrift

et al. 2023

Sci. Adv.

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Organic aerosol (OA) is an air pollutant ubiquitous in urban atmospheres. Urban OA is usually apportioned into primary OA (POA), mostly emitted by mobile sources, and secondary OA (SOA), which forms in the atmosphere due to oxidation of gas-phase precursors from anthropogenic and biogenic sources. By performing coordinated measurements in the particle phase and the gas phase, we show that the alkylperoxy radical chemistry that is responsible for low-temperature ignition also leads to the formation of oxygenated POA (OxyPOA). OxyPOA is distinct from POA emitted during high-temperature ignition and is chemically similar to SOA. We present evidence for the prevalence of OxyPOA in emissions of a spark-ignition engine and a next-generation advanced compression-ignition engine, highlighting the importance of understanding OxyPOA for predicting urban air pollution patterns in current and future atmospheres.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Alkylperoxy radicals are responsible for the formation of oxygenated primary organic aerosol

El Hajj,

Hartness,

Vandergrift

et al. 2023

Sci. Adv.

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“…In the latest THF low-T JSR study, Koritzke et al 25 focused on understanding the effect of O 2 concentration on product formation and on providing isomer-resolved detection and quantification of some major species, such as butanedial. Koritzke et al compared the measured concentrations with model predictions using the Fenard et al mechanism and a modified version incorporating updated chemistry for furan and 2,3-dihydrofuran from Wu et al 26 and found discrepancies.…”

Section: Introductionmentioning

confidence: 99%

Time-resolved quantification of key species and mechanistic insights in low-temperature tetrahydrofuran oxidation

Demireva,

Au,

Hansen

et al. 2024

Phys. Chem. Chem. Phys.

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“… 6 , 7 For instance, concentration profiles of cyclic ethers are linked to that of the parent QOOH radicals. While the detection of cyclic ethers using, for instance, VUV photoionization mass spectrometry 8 , 9 and VUV absorption 10 , 33 is well established, the correct inference of QOOH concentrations requires that the loss mechanisms of these cyclic ethers are also well characterized and accounted for in chemical kinetics modeling.…”

Section: Introductionmentioning

confidence: 99%

“…Owing to extreme difficulty in experimental detection, − especially in reacting systems, immediate decomposition products are relied upon to infer the presence and concentration of QOOH radicals. , For instance, concentration profiles of cyclic ethers are linked to that of the parent QOOH radicals. While the detection of cyclic ethers using, for instance, VUV photoionization mass spectrometry , and VUV absorption , is well established, the correct inference of QOOH concentrations requires that the loss mechanisms of these cyclic ethers are also well characterized and accounted for in chemical kinetics modeling.…”

Section: Introductionmentioning

confidence: 99%

Unimolecular Reactions of 2,4-Dimethyloxetanyl Radicals

Doner¹,

Zádor

Rotavera³

2023

J. Phys. Chem. A

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Alkyl-substituted oxetanes are cyclic ethers formed via unimolecular reactions of QOOH radicals produced via a six-membered transition state in the preceding isomerization step of organic peroxy radicals, ROO. Owing to radical isomer-specific formation pathways, cyclic ethers are unambiguous proxies for inferring QOOH reaction rates. Therefore, accounting for subsequent oxidation of cyclic ethers is important in order to accurately determine rates for QOOH → products. Cyclic ethers can react via unimolecular reaction (ring-opening) or via bimolecular reaction with O 2 to form cyclic ether-peroxy adducts. The computations herein provide reaction mechanisms and theoretical rate coefficients for the former type in order to determine competing pathways for the cyclic ether radicals. Rate coefficients of unimolecular reactions of 2,4-dimethyloxetanyl radicals were computed using master equation modeling from 0.01 to 100 atm and from 300 to 1000 K. Coupled-cluster methods were utilized for stationary-point energy calculations, and uncertainties in the computed rate coefficients were accounted for using variation in barrier heights and in well depths. The potential energy surfaces reveal accessible channels to several species via crossover reactions, such as 2-methyltetrahydrofuran-5-yl and pentanonyl isomers. For the range of temperature over which 2,4-dimethyloxetane forms during n-pentane oxidation, the following are the major channels: 2,4dimethyloxetan-1-yl → acetaldehyde + allyl, 2,4-dimethyloxetan-2-yl → propene + acetyl, and 2,4-dimethyloxetan-3-yl → 3-butenal + methyl, or, 1-penten-3-yl-4-ol. Well-skipping reactions were significant in a number of channels and also exhibited a markedly different pressure dependence. The calculations show that rate coefficients for ring-opening are approximately an order of magnitude lower for the tertiary 2,4-dimethyloxetanyl radicals than for the primary and secondary 2,4-dimethyloxetanyl radicals. Unlike for reactions of the corresponding ROO radicals, however, unimolecular rate coefficients are independent of the stereochemistry. Moreover, rate coefficients of cyclic ether radical ring-opening are of the same order of magnitude as O 2 addition, underscoring the point that a competing network of reactions is necessary to include for accurate chemical kinetics modeling of species profiles for cyclic ethers.

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Probing O2-dependence of tetrahydrofuranyl reactions via isomer-resolved speciation

Cited by 5 publications

References 42 publications

Alkylperoxy radicals are responsible for the formation of oxygenated primary organic aerosol

Alkylperoxy radicals are responsible for the formation of oxygenated primary organic aerosol

Time-resolved quantification of key species and mechanistic insights in low-temperature tetrahydrofuran oxidation

Unimolecular Reactions of 2,4-Dimethyloxetanyl Radicals

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