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

   https://doi.org/10.1039/d0cp05018k  

   Vansco, Michael F.; Caravan, Rebecca L.; Pandit, Shubhrangshu; Zuraski, Kristen; Winiberg, Frank A.; Au, Kendrew; Bhagde, Trisha; Trongsiriwat, Nisalak; Walsh, Patrick J.; Osborn, David L.; et al (December 2020, Physical Chemistry Chemical Physics)

   null (Ed.)

   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 (R 1 R 2 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 (D 2 -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 D 2 -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. 

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2. Direct kinetic measurements and theoretical predictions of an isoprene-derived Criegee intermediate

   https://doi.org/10.1073/pnas.1916711117  

   Caravan, Rebecca L.; Vansco, Michael F.; Au, Kendrew; Khan, M. Anwar H.; Li, Yu-Lin; Winiberg, Frank A. F.; Zuraski, Kristen; Lin, Yen-Hsiu; Chao, Wen; Trongsiriwat, Nisalak; et al (April 2020, Proceedings of the National Academy of Sciences)

   Isoprene has the highest emission into Earth’s atmosphere of any nonmethane hydrocarbon. Atmospheric processing of alkenes, including isoprene, via ozonolysis leads to the formation of zwitterionic reactive intermediates, known as Criegee intermediates (CIs). Direct studies have revealed that reactions involving simple CIs can significantly impact the tropospheric oxidizing capacity, enhance particulate formation, and degrade local air quality. Methyl vinyl ketone oxide (MVK-oxide) is a four-carbon, asymmetric, resonance-stabilized CI, produced with 21 to 23% yield from isoprene ozonolysis, yet its reactivity has not been directly studied. We present direct kinetic measurements of MVK-oxide reactions with key atmospheric species using absorption spectroscopy. Direct UV-Vis absorption spectra from two independent flow cell experiments overlap with the molecular beam UV-Vis-depletion spectra reported recently [M. F. Vansco, B. Marchetti, M. I. Lester,J. Chem. Phys.149, 44309 (2018)] but suggest different conformer distributions under jet-cooled and thermal conditions. Comparison of the experimental lifetime herein with theory indicates only thesyn-conformers are observed;anti-conformers are calculated to be removed much more rapidly via unimolecular decay. We observe experimentally and predict theoretically fast reaction ofsyn-MVK-oxide with SO₂and formic acid, similar to smaller alkyl-substituted CIs, and by contrast, slow removal in the presence of water. We determine products through complementary multiplexed photoionization mass spectrometry, observing SO₃and identifying organic hydroperoxide formation from reaction with SO₂and formic acid, respectively. The tropospheric implications of these reactions are evaluated using a global chemistry and transport model. 

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3. Ozonolysis of phenolic aldehydes from industrial-based lignin wastewaters

   https://doi.org/10.1016/j.scitotenv.2025.180190  

   Witt, Reagan Patton; Todd, Mia B; Oladele, Motunrayo E; Guzman, Marcelo I (August 2025, Science of The Total Environment)

   Gan, Jay; Hopke, Philip; Ouyang, Wei; Paoletti, Elena (Ed.)

   Phenolic aldehydes are widespread pollutants in water and soil, originating from lignin-based agro-industries. With increasing wastewater pollution, improved treatment systems are necessary to degrade phenolic aldehydes into less hazardous compounds. Over the past two decades, ozonolysis wastewater treatment has been implemented in the United States, Japan, and South Korea. However, the mechanistic understanding of phenolic aldehyde ozonolysis in water remains incomplete. This study investigates the ozonolysis of three model phenolic aldehydes (syringaldehyde, vanillin, 4-hydroxybenzaldehyde) in representative concentrations for wastewater of 0.5–1.5 mM and pH 4–8. Each compound solution was sparged for 30 min at a fixed O3(g) flow (0.20 to 1.00 L min−1), providing steady-state dissolved concentrations of 5.4 to 16.2 μM. Reactant loss and product generation were monitored using UV–visible (UV–vis) spectroscopy, ultra-high pressure liquid chromatography (UHPLC) with UV–vis and mass spectrometry (MS) detection, and ion chromatography with conductivity and MS detection of anions. Identified products based on their mass-to-charge ratio (m/z−) included oxalic acid (89), glycolic acid (75), formic acid (45), and maleic acid (115). Additional intermediate products were identified under various reaction conditions, revealing competing mechanisms in the degradative oxidation of aqueous phenolic aldehydes exposed to O3(g). A unifying mechanism is proposed to explain the production of smaller, less toxic molecules during phenolic aldehyde ozonolysis, enhancing water quality. This mechanism serves as a basis for evaluating the implementation of ozonolysis in scaled-up water treatment processes. 

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4. Thermochemistry of the Smallest QOOH Radical from the Roaming Fragmentation of Energy Selected Methyl Hydroperoxide Ions

   https://doi.org/10.1039/c8cp03168a  

   Covert, Kyle C.; Voronova, Krisztina; Torma, Krisztián G.; Bodi, Andras; Zádor, Judit; Sztáray, Balint (January 2018, Physical Chemistry Chemical Physics)

   The dissociative photoionization processes of methyl hydroperoxide (CH 3 OOH) have been studied by imaging Photoelectron Photoion Coincidence (iPEPICO) spectroscopy experiments as well as quantum-chemical and statistical rate calculations. Energy selected CH 3 OOH + ions dissociate into CH 2 OOH + , HCO + , CH 3 + , and H 3 O + ions in the 11.4–14.0 eV photon energy range. The lowest-energy dissociation channel is the formation of the cation of the smallest “QOOH” radical, CH 2 OOH + . An extended RRKM model fitted to the experimental data yields a 0 K appearance energy of 11.647 ± 0.005 eV for the CH 2 OOH + ion, and a 74.2 ± 2.6 kJ mol –1 mixed experimental-theoretical 0 K heat of formation for the CH 2 OOH radical. The proton affinity of the Criegee intermediate, CH 2 OO, was also obtained from the heat of formation of CH 2 OOH + (792.8 ± 0.9 kJ mol –1 ) to be 847.7 ± 1.1 kJ mol –1 , reducing the uncertainty of the previously available computational value by a factor of 4. RRKM modeling of the complex web of possible rearrangement-dissociation processes were used to model the higher-energy fragmentation. Supported by Born–Oppenheimer molecular dynamics simulations, we found that the HCO + fragment ion is produced through a roaming transition state followed by a low barrier. H 3 O + is formed in a consecutive process from the CH 2 OOH + fragment ion, while direct C–O fission of the molecular ion leads to the methyl cation. 

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5. Sulfur Dioxide Modifies Aerosol Particle Formation and Growth by Ozonolysis of Monoterpenes and Isoprene

   https://doi.org/10.1029/2018JD030064  

   Stangl, Christopher M.; Krasnomowitz, Justin M.; Apsokardu, Michael J.; Tiszenkel, Lee; Ouyang, Qi; Lee, Shanhu; Johnston, Murray V. (April 2019, Journal of Geophysical Research: Atmospheres)

   Abstract The effect of sulfur dioxide on particle formation and growth by ozonolysis of three monoterpenes (α‐pinene,β‐pinene, and limonene) and isoprene was investigated in the presence of monodisperse ammonium sulfate seed particles and an OH scavenger in a flow tube under dry conditions. Without sulfur dioxide, new particle formation was not observed, and seed particle growth was consistent with condensation of low‐volatility oxidation products produced from each organic precursor. With sulfur dioxide, new particle formation was observed from every precursor studied, consistent with sulfuric acid formation by reaction of sulfur dioxide with stabilized Criegee Intermediates. The presence of sulfur dioxide did not significantly affect seed particle growth rates fromα‐pinene and limonene ozonolysis, although chemical composition measurements revealed the presence of organosulfates in the particles following SO₂exposure. Contrarily, the growth of seeds byβ‐pinene and isoprene ozonolysis was considerably enhanced by sulfur dioxide, and chemical composition measurements revealed that the enhanced growth was not due to additional organic material, suggesting that inorganic sulfate was likely responsible. The results suggest that a previously unconsidered particle‐phase pathway to growth activated by sulfur dioxide may alter production of cloud condensation nuclei over regions with significant SO₂‐alkene interactions. 

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