Title: Reaction mechanisms of a cyclic ether intermediate: Ethyloxirane

Abstract

Oxiranes are a class of cyclic ethers formed in abundance during low-temperature combustion of hydrocarbons and biofuels, either via chain-propagating steps that occur from unimolecular decomposition of β-hydroperoxyalkyl radicals (β-˙QOOH) or from reactions of HOÓ with alkenes. Ethyloxirane is one of four alkyl-substituted cyclic ether isomers produced as an intermediate from n-butane oxidation. While rate coefficients for β-˙QOOH → ethyloxirane + ÓH are reported extensively, subsequent reaction mechanisms of the cyclic ether are not. As a result, chemical kinetics mechanisms commonly adopt simplified chemistry to describe ethyloxirane consumption by convoluting several elementary reactions into a single step, which may introduce mechanism truncation error—uncertainty derived from missing or incomplete chemistry. Here we provide fundamental insight on reaction mechanisms of ethyloxirane in support of ongoing efforts to minimize mechanism truncation error. Reaction mechanisms are inferred from the detection of products during chlorine atom-initiated oxidation experiments using multiplexed photoionization mass spectrometry conducted at 10 Torr and temperatures of 650 K and 800 K. To complement the experiments, calculations of stationary point energies were conducted using the ccCA-PS3 composite method on ˙R + O₂ potential energy surfaces for the four ethyloxiranyl radical isomers, which produced barrier heights for 24 reaction pathways. In addition to productsmore » from ˙QOOH → cyclic ether + ÓH and ˙R + O₂ → conjugate alkene + HOÓ, both of which were significant pathways and are prototypical to alkane oxidation, other species were identified from ring-opening of both ethyloxiranyl and ˙QOOH radicals. The latter occurs when the unpaired electron is localized on the ether group, causing the initial ˙QOOH structure to ring-open and form a resonance-stabilized ketohydroperoxide-type radical. The present work provides the first analysis of ethyloxirane oxidation chemistry, which reveals that consumption pathways are complex and may require an expansion of submechanisms to increase the fidelity of chemical kinetics mechanisms.« less

Authors:

Christianson, Matthew G.  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-2142-6580"

Doner, Anna C.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-2686-198X"

Davis, Matthew M.  ^[2];

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• Search DOE PAGES for ORCID "0000-0003-4831-5776"

Koritzke, Alanna L.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-3522-2442"

Turney, Justin M.  ^[3];

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• Search DOE PAGES for ORCID "0000-0003-3659-0711"

Schaefer, Henry F.  ^[2];

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• Search DOE PAGES for ORCID "0000-0003-0252-2083"

Sheps, Leonid  ^[4];

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• Search DOE PAGES for ORCID "0000-0003-4320-0865"

Osborn, David L.  ^[4];

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• Search DOE PAGES for ORCID "0000-0003-4304-8218"

Taatjes, Craig A.  ^[4];

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• Search DOE PAGES for ORCID "0000-0002-9271-0282"

Rotavera, Brandon  ^[5]

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• Search DOE PAGES for ORCID "0000-0003-0533-7131"

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+ Show Author Affiliations

1. Univ. of Georgia, Athens, GA (United States). Dept. of Chemistry
2. Univ. of Georgia, Athens, GA (United States). Dept. of Chemistry and Center for Computational Quantum Chemistry
3. Univ. of Georgia, Athens, GA (United States). Center for Computational Quantum Chemistry
4. Sandia National Lab. (SNL-CA), Livermore, CA (United States). Combustion Research Facility
5. Univ. of Georgia, Athens, GA (United States). Dept. of Chemistry and College of Engineering

Publication Date:

Mon Sep 21 00:00:00 EDT 2020

Research Org.:

Sandia National Lab. (SNL-CA), Livermore, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division; USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1667429

Report Number(s):

SAND-2020-9545J
Journal ID: ISSN 0538-8066; 690501

Grant/Contract Number:  

AC04-94AL85000; NA0003525; AC02-05CH11231; SC0018412

Resource Type:

Accepted Manuscript

Journal Name:

International Journal of Chemical Kinetics

Additional Journal Information:

Journal Volume: 53; Journal Issue: 1; Journal ID: ISSN 0538-8066

Publisher:

Wiley

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; cyclic ether; primary intermediate; n-butane; MPIMS; QOOH