Lockhart, J, Blitz, MA, Heard, DE et al. (2 more authors) (2013) Mechanism of the reaction of OH with alkynes in the presence of oxygen. Journal of Physical Chemistry A, 117 (26). 5407 - 5418. ISSN 1089-5639
Abstract
Previous work has shown that the branching ratio of the reaction of OH/C2H2/O2 to glyoxal and formic acid is dependent on oxygen fraction, and a significant component of the product yield under atmospheric conditions is formed from reaction of chemically activated OH-C2H2 adduct. In this article, isotopic substitution is used to determine the mechanism of the OH/C2H2/O2 reaction resolving previous contradictory observations in the literature. Using laser flash photolysis and probing OH concentrations via laser induced fluorescence, a rate coefficient of kHO-C2H2+O2 = (6.17 ± 0.68) × 10(-12) cm(3) molecule(-1) s(-1) is determined at 298 K from the analysis of biexponential OH decays in the presence of C2H2 and low concentrations of O2. The studies have been extended to propyne and but-2-yne. The reactions of OH with propyne and but-2-yne have been studied as a function of pressure in the absence of oxygen. The reaction of OH with propyne is in the fall off region from 2-25 Torr of nitrogen at room temperature. A pressure independent value of (4.21 ± 0.47) × 10(-12) cm(3) molecule(-1) s(-1) was obtained from averaging the eight independent measurements at 25 and 75 Torr. The reaction of OH with but-2-yne at 298 K is pressure independent (5-25 Torr N2) with a value of (1.87 ± 0.19) × 10(-11) cm(3) molecule(-1) s(-1). Analysis of biexpontial OH decays in alkyne/low O2 conditions gives the following rate coefficients at 298 K: kHO-C3H4+O2 = (8.00 ± 0.82) × 10(-12) cm(3) molecule(-1) s(-1) and kHO-C4H6+O2 = (6.45 ± 0.68) × 10(-12) cm(3) molecule(-1) s(-1). The branching ratio of bicarbonyl to organic acid in the presence of excess oxygen also shows an oxygen fraction dependence for propyne and but-2-yne, qualitatively similar to that for acetylene. For an oxygen fraction of 0.2 at 298 K, pressure independent yields of methylglyoxal (0.70 ± 0.03) and biacetyl (0.74 ± 0.03) were determined for the propyne and but-2-yne systems, respectively. The yield of acid increases with temperature from 212-500 K. Master equation calculations show that, under atmospheric conditions, the acetyl cofragment of organic acid production will dissociate, consistent with experimental observations.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2013 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Physical Chemistry A, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/jp404233b |
Keywords: | Alkynes; Formates; Glyoxal; Hydroxides; Molecular Structure; Oxygen |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Chemistry (Leeds) > Physical Chemistry (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 11 Nov 2015 15:58 |
Last Modified: | 16 Jan 2018 16:00 |
Published Version: | http://dx.doi.org/10.1021/jp404233b |
Status: | Published |
Publisher: | American Chemical Society |
Identification Number: | 10.1021/jp404233b |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:87631 |