Formic acid catalyzed isomerization and adduct formation of an isoprene-derived Criegee intermediate: experiment and theory. Issue 46 (19th November 2020)

• Record Type: Journal Article
• Authors: Vansco, Michael F.; Caravan, Rebecca L.; Pandit, Shubhrangshu; Zuraski, Kristen; Winiberg, Frank A. F.; Au, Kendrew; Bhagde, Trisha; Trongsiriwat, Nisalak; Walsh, Patrick J.; Osborn, David L.; Percival, Carl J.; Klippenstein, Stephen J.; Taatjes, Craig A.; Lester, Marsha I.
• Is Part Of: Physical chemistry chemical physics. Volume 22:Issue 46(2020)
• Page Start: 26796
• Page End: 26805
• Publication Date: 2020-11-19
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d0cp05018k
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Investigation of key reaction pathways for an isoprene-derived Criegee intermediate with formic acid: acid catalyzed isomerization and adduct formation. 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 (R1 R2 C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.