Formic acid catalyzed isomerization and adduct formation of an isoprene-derived Criegee intermediate: experiment and theory

Michael F. Vansco; Rebecca L. Caravan; Shubhrangshu Pandit; Kristen Zuraski; Frank A. F. Winiberg; Kendrew Au; Trisha Bhagde; Nisalak Trongsiriwat; Patrick J. Walsh; David L. Osborn; Carl J. Percival; Stephen J. Klippenstein; Craig A. Taatjes; Marsha I. Lester

doi:10.1039/D0CP05018K

Formic acid catalyzed isomerization and adduct formation of an isoprene-derived Criegee intermediate: experiment and theory†

Michael F. Vansco,

^a Rebecca L. Caravan,

*^bcd Shubhrangshu Pandit,

^ae Kristen Zuraski,

^b Frank A. F. Winiberg,

^fg Kendrew Au,^c Trisha Bhagde,

^a Nisalak Trongsiriwat,^a Patrick J. Walsh,

^a David L. Osborn,

^c Carl J. Percival,

^f Stephen J. Klippenstein,

^d Craig A. Taatjes

^c and Marsha I. Lester

*^a

Author affiliations

* Corresponding authors

^a Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA
E-mail: milester@sas.upenn.edu

^b NASA Postdoctoral Program Fellow, NASA Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA

^c Combustion Research Facility, Mailstop 9055, Sandia National Laboratories, Livermore, CA 94551, USA

^d Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL 60439, USA
E-mail: caravarl@anl.gov

^e Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA 92093, USA

^f NASA Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA

^g Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA

Abstract

Isoprene is the most abundant non-methane hydrocarbon emitted into the Earth's atmosphere. Ozonolysis is an important atmospheric sink for isoprene, which generates reactive carbonyl oxide species (R₁R₂C [double bond, length as m-dash] O⁺O⁻) known as Criegee intermediates. This study focuses on characterizing the catalyzed isomerization and adduct formation pathways for the reaction between formic acid and methyl vinyl ketone oxide (MVK-oxide), a four-carbon unsaturated Criegee intermediate generated from isoprene ozonolysis. syn-MVK-oxide undergoes intramolecular 1,4 H-atom transfer to form a substituted vinyl hydroperoxide intermediate, 2-hydroperoxybuta-1,3-diene (HPBD), which subsequently decomposes to hydroxyl and vinoxylic radical products. Here, we report direct observation of HPBD generated by formic acid catalyzed isomerization of MVK-oxide under thermal conditions (298 K, 10 torr) using multiplexed photoionization mass spectrometry. The acid catalyzed isomerization of MVK-oxide proceeds by a double hydrogen-bonded interaction followed by a concerted H-atom transfer via submerged barriers to produce HPBD and regenerate formic acid. The analogous isomerization pathway catalyzed with deuterated formic acid (D₂-formic acid) enables migration of a D atom to yield partially deuterated HPBD (DPBD), which is identified by its distinct mass (m/z 87) and photoionization threshold. In addition, bimolecular reaction of MVK-oxide with D₂-formic acid forms a functionalized hydroperoxide adduct, which is the dominant product channel, and is compared to a previous bimolecular reaction study with normal formic acid. Complementary high-level theoretical calculations are performed to further investigate the reaction pathways and kinetics.

This article is part of the themed collection: 2020 PCCP HOT Articles

Physical Chemistry Chemical Physics

Formic acid catalyzed isomerization and adduct formation of an isoprene-derived Criegee intermediate: experiment and theory†

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Formic acid catalyzed isomerization and adduct formation of an isoprene-derived Criegee intermediate: experiment and theory

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