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Title: Low Temperature Chlorine-Initiated Oxidation of Small-Chain Methyl Esters: Quantification of Chain-Terminating HO 2-Elimination Channels

Abstract

In this paper, Cl-initiated oxidation reactions of three small-chain methyl esters, methyl propanoate (CH 3CH 2COOCH 3; MP), methyl butanoate (CH 3CH 2CH 2COOCH 3; MB), and methyl valerate (CH 3CH 2CH 2CH 2COOCH 3; MV), are studied at 1 or 8 Torr and 550 and 650 K. Products are monitored as a function of mass, time, and photoionization energy using multiplexed photoionization mass spectrometry coupled to tunable synchrotron photoionization radiation. Pulsed photolysis of molecular chlorine is the source of Cl radicals, which remove an H atom from the ester, forming a free radical. In each case, after addition of O 2 to the initial radicals, chain-terminating HO 2-elimination reactions are observed to be important. Branching ratios among competing HO 2-elimination channels are determined via absolute photoionization spectra of the unsaturated methyl ester coproducts. At 550 K, HO 2-elimination is observed to be selective, resulting in nearly exclusive production of the conjugated methyl ester coproducts, methyl propenoate, methyl-2-butenoate, and methyl-2-pentenoate, respectively. However, in MV, upon raising the temperature to 650 K, other HO 2-elimination pathways are observed that yield methyl-3-pentenoate and methyl-4-pentenoate. In each methyl ester oxidation reaction, a peak is observed at a mass consistent with cyclic ether formation,more » indicating chain-propagating OH loss/ring formation pathways via QOOH intermediates. Evidence is observed for the participation of resonance-stabilized QOOH in the most prominent cyclic ether pathways. Finally, stationary point energies for HO 2-elimination pathways and select cyclic ether formation channels are calculated at the CBS-QB3 level of theory and assist in the assignment of reaction pathways and final products.« less

Authors:
 [1];  [2];  [3];  [3];  [1]
  1. Univ. of San Francisco, CA (United States)
  2. Pacific Gas and Electric Company, San Francisco, CA (United States)
  3. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-CA), Livermore, CA (United States); Univ. of San Francisco, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE National Nuclear Security Administration (NNSA); SNL Laboratory Directed Research and Development (LDRD) Program; Univ. of San Francisco (United States)
OSTI Identifier:
1472257
Report Number(s):
SAND2018-9564J
Journal ID: ISSN 1089-5639; 667489
Grant/Contract Number:  
AC04-94AL85000; AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory
Additional Journal Information:
Journal Volume: 120; Journal Issue: 10; Journal ID: ISSN 1089-5639
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Muller, Giel, Scheer, Adam, Osborn, David L., Taatjes, Craig A., and Meloni, Giovanni. Low Temperature Chlorine-Initiated Oxidation of Small-Chain Methyl Esters: Quantification of Chain-Terminating HO2-Elimination Channels. United States: N. p., 2016. Web. doi:10.1021/acs.jpca.6b00148.
Muller, Giel, Scheer, Adam, Osborn, David L., Taatjes, Craig A., & Meloni, Giovanni. Low Temperature Chlorine-Initiated Oxidation of Small-Chain Methyl Esters: Quantification of Chain-Terminating HO2-Elimination Channels. United States. doi:10.1021/acs.jpca.6b00148.
Muller, Giel, Scheer, Adam, Osborn, David L., Taatjes, Craig A., and Meloni, Giovanni. Wed . "Low Temperature Chlorine-Initiated Oxidation of Small-Chain Methyl Esters: Quantification of Chain-Terminating HO2-Elimination Channels". United States. doi:10.1021/acs.jpca.6b00148. https://www.osti.gov/servlets/purl/1472257.
@article{osti_1472257,
title = {Low Temperature Chlorine-Initiated Oxidation of Small-Chain Methyl Esters: Quantification of Chain-Terminating HO2-Elimination Channels},
author = {Muller, Giel and Scheer, Adam and Osborn, David L. and Taatjes, Craig A. and Meloni, Giovanni},
abstractNote = {In this paper, Cl-initiated oxidation reactions of three small-chain methyl esters, methyl propanoate (CH3CH2COOCH3; MP), methyl butanoate (CH3CH2CH2COOCH3; MB), and methyl valerate (CH3CH2CH2CH2COOCH3; MV), are studied at 1 or 8 Torr and 550 and 650 K. Products are monitored as a function of mass, time, and photoionization energy using multiplexed photoionization mass spectrometry coupled to tunable synchrotron photoionization radiation. Pulsed photolysis of molecular chlorine is the source of Cl radicals, which remove an H atom from the ester, forming a free radical. In each case, after addition of O2 to the initial radicals, chain-terminating HO2-elimination reactions are observed to be important. Branching ratios among competing HO2-elimination channels are determined via absolute photoionization spectra of the unsaturated methyl ester coproducts. At 550 K, HO2-elimination is observed to be selective, resulting in nearly exclusive production of the conjugated methyl ester coproducts, methyl propenoate, methyl-2-butenoate, and methyl-2-pentenoate, respectively. However, in MV, upon raising the temperature to 650 K, other HO2-elimination pathways are observed that yield methyl-3-pentenoate and methyl-4-pentenoate. In each methyl ester oxidation reaction, a peak is observed at a mass consistent with cyclic ether formation, indicating chain-propagating OH loss/ring formation pathways via QOOH intermediates. Evidence is observed for the participation of resonance-stabilized QOOH in the most prominent cyclic ether pathways. Finally, stationary point energies for HO2-elimination pathways and select cyclic ether formation channels are calculated at the CBS-QB3 level of theory and assist in the assignment of reaction pathways and final products.},
doi = {10.1021/acs.jpca.6b00148},
journal = {Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory},
number = 10,
volume = 120,
place = {United States},
year = {2016},
month = {2}
}

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