Heterogeneous Oxidation of Catechol

Abstract

Natural and anthropogenic emissions of aromatic hydrocarbons from biomass burning, agro-industrial settings, and fossil fuel combustion contribute precursors to secondary aerosol formation (SOA). How these compounds are processed under humid tropospheric conditions is the focus of current attention to understand their environmental fate. This work shows how catechol thin films, a model for oxygenated aromatic hydrocarbons present in biomass burning and combustion aerosols, undergo heterogeneous oxidation at the air-solid interface under variable relative humidity (RH = 0-90%). The maximum reactive uptake coefficient of O3(g) by catechol γO3 = (7.49 ± 0.35) × 10(-6) occurs for 90% RH. Upon exposure of ca. 104-μm thick catechol films to O3(g) mixing ratios between 230 ppbv and 25 ppmv, three main reaction pathways are observed. (1) The cleavage of the 1,2 carbon-carbon bond at the air-solid interface resulting in the formation of cis,cis-muconic acid via primary ozonide and hydroperoxide intermediates. Further direct ozonolysis of cis,cis-muconic yields glyoxylic, oxalic, crotonic, and maleic acids. (2) A second pathway is evidenced by the presence of Baeyer-Villiger oxidation products including glutaconic 4-hydroxy-2-butenoic and 5-oxo-2-pentenoic acids during electrospray ionization mass spectrometry (MS) and ion chromatography MS analyses. (3) Finally, indirect oxidation by in situ produced hydroxyl radical (HO(•)) results in the generation of semiquinone radical intermediates toward the synthesis of polyhydoxylated aromatic rings such as tri-, tetra-, and penta-hydroxybenzene. Remarkably, heavier polyhydroxylated biphenyl and terphenyl products present in the extracted oxidized films result from coupling reactions of semiquinones of catechol and its polyhydroxylated rings. The direct ozonolysis of 1,2,3- and 1,2,4-trihydroxybenezene yields 2- and 3-hydroxy-cis,cis-muconic acid, respectively. The production of 2,4- or 3,4-dihdroxyhex-2-enedioic acid is proposed to result from the sequential processing of cis,cis-muconic acid, 2- and 3-hydroxy-cis,cis-muconic acid. Overall, these reactions contribute precursors to form aqueous SOA from aromatics in atmospheric aerosols and brown clouds.

Degradation of the cellulosic key chromophores 2,5- and 2,6-dihydroxyacetophenone by hydrogen peroxide under alkaline conditions. Chromophores in cellulosics, XVII

“…GC-MS used a previously developed analysis method for mixtures of acids, aldehydes, ketoacids and hydroxyacids in complex matrices that is based on oximation/trimethylsilylation. The analytical results agree largely with those from similar bleaching experiments (Juretic et al 2013;Pillar et al 2014Pillar et al , 2015. The products are the same for both chromophores, which is a result of the degradation pathway as delineated above, involving an initial Baeyer-Villiger type oxidation with acetic acid as the leaving group, subsequent oxidation of the resulting trihydroxybenzene isomers to the corresponding quinones and further oxidation under ring-fragmentation to muconic acids.…”

Oxidation of Substituted Catechols at the Air–Water Interface: Production of Carboxylic Acids, Quinones, and Polyphenols

“…2,3 Furthermore, the common products identified during offline analysis of reactions lasting a few hours and in situ studies under a few microseconds of contact time (τ c ) validated a flowthrough ultrafast interfacial oxidation MS setup for inspecting reactions at the air−water interface. 2,3 Combustion and biomass burning emissions provide the two main aromatic species to the atmosphere, benzene and toluene, that total 5.6 and 6.9 Tg of C y −1 , respectively. 7 We have previously explained that the oxidative processing of benzene by hydroxyl radicals (HO • ) consecutively yields phenol (reaction R1, Scheme 1) and dihydroxybenzenes such as catechol (reaction R2) with gas-phase rate constants k R1;benzene+HO • = 1.2 × 10 −12 cm 3 molecule −1 s −1 8 and k R2;phenol+HO • = 2.7 × 10 −11 cm 3 molecule −1 s −1 , 9 respectively.…”

“…1 Aromatic species emitted to the atmosphere during fossil fuel combustion and biomass burning (e.g., wildfires) processes provide phenol precursors for SOA formation through competing fragmentation and functionalization oxidation reactions. 2,3 Previous work has explored the catalytic effect played by interfaces and the role of variable relative humidity (RH) during the atmospheric oxidation of phenols, e.g., by O 3 (g) and hydroxyl radicals (HO • ). 2−6 A combination of analytical methods (infrared spectroscopy, mass spectrometry (MS), and chromatography) employed in our laboratory revealed the importance of competitive oxidation mechanisms.…”

“…2−6 A combination of analytical methods (infrared spectroscopy, mass spectrometry (MS), and chromatography) employed in our laboratory revealed the importance of competitive oxidation mechanisms. 2,3 The production of several reactive oxygen species (ROS), including the formation of semiquinone radicals, has been demonstrated, 2,3 suggesting that aromatics provide a significant missing mechanism for the production of low-volatility species found in aerosols. 2,3 Furthermore, the common products identified during offline analysis of reactions lasting a few hours and in situ studies under a few microseconds of contact time (τ c ) validated a flowthrough ultrafast interfacial oxidation MS setup for inspecting reactions at the air−water interface.…”

“…2,3 The production of several reactive oxygen species (ROS), including the formation of semiquinone radicals, has been demonstrated, 2,3 suggesting that aromatics provide a significant missing mechanism for the production of low-volatility species found in aerosols. 2,3 Furthermore, the common products identified during offline analysis of reactions lasting a few hours and in situ studies under a few microseconds of contact time (τ c ) validated a flowthrough ultrafast interfacial oxidation MS setup for inspecting reactions at the air−water interface. 2,3 Combustion and biomass burning emissions provide the two main aromatic species to the atmosphere, benzene and toluene, that total 5.6 and 6.9 Tg of C y −1 , respectively.…”