Low Temperature Chlorine-Initiated Oxidation of Small-Chain Methyl Esters: Quantification of Chain-Terminating HO2-Elimination Channels
- Univ. of San Francisco, CA (United States)
- Pacific Gas and Electric Company, San Francisco, CA (United States)
- Sandia National Lab. (SNL-CA), Livermore, CA (United States)
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.
- Research Organization:
- Sandia National Lab. (SNL-CA), Livermore, CA (United States); Univ. of San Francisco, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE National Nuclear Security Administration (NNSA); SNL Laboratory Directed Research and Development (LDRD) Program; Univ. of San Francisco (United States)
- Grant/Contract Number:
- AC04-94AL85000; AC02-05CH11231
- OSTI ID:
- 1472257
- Report Number(s):
- SAND2018-9564J; 667489
- Journal Information:
- Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory, Vol. 120, Issue 10; ISSN 1089-5639
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Study of low temperature chlorine atom initiated oxidation of methyl and ethyl butyrate using synchrotron photoionization TOF-mass spectrometry
|
journal | January 2018 |
Quantum chemical study of the ( Z )-2-penten-1-ol (HOCH 2 –CH = CHCH 2 CH 3 ) + OH + O 2 reactions
|
journal | September 2016 |
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