Issue 36, 2024

Theoretical analysis of the OH-initiated atmospheric oxidation reactions of imidazole

Abstract

Imidazoles are present in Earth's atmosphere in both the gas-phase and in aerosol particles, and have been implicated in the formation of brown carbon aerosols. The gas-phase oxidation of imidazole (C3N2H4) by hydroxyl radicals has been shown to be preferentially initiated via OH-addition to position C5, producing the 5-hydroxyimidazolyl radical adduct. However, the fate of this adduct upon reaction with O2 in the atmospheric gas-phase is currently unknown. We employed an automated approach to investigate the reaction mechanism and kinetics of imidazole's OH-initiated gas-phase oxidation, in the presence of O2 and NOx. The explored mechanism included reactions available to first-generation RO2 radicals, as well as alkoxyl radicals produced from RO2 + NO reactions. Product distributions were obtained by assembling and solving a master equation, under conditions relevant to the Earth's atmosphere. Our calculations show a complex, branched reaction mechanism, which nevertheless converges to yield two major closed-shell products: 4H-imidazol-4-ol (4H-4ol) and N,N′-diformylformamidine (FMF). At 298 K and 1 atm, we estimate the yields of 4H-4ol and FMF from imidazole oxidation initiated via OH-addition to position C5 to be 34 : 66, 12 : 85 and 2 : 95 under 10 ppt, 100 ppt and 1 ppb of NO respectively. This work also revealed O2-migration pathways between the α-N-imino peroxyl radical isomers. This reaction channel is fast for the first-generation RO2 radicals, and may be important during the atmospheric oxidation of other unsaturated organic nitrogen compounds as well.

Graphical abstract: Theoretical analysis of the OH-initiated atmospheric oxidation reactions of imidazole

Supplementary files

Article information

Article type
Paper
Submitted
21 May 2024
Accepted
26 Jul 2024
First published
29 Jul 2024
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2024,26, 23570-23587

Theoretical analysis of the OH-initiated atmospheric oxidation reactions of imidazole

T. Golin Almeida, C. Martí, T. Kurtén, J. Zádor and S. L. Johansen, Phys. Chem. Chem. Phys., 2024, 26, 23570 DOI: 10.1039/D4CP02103G

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