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Please use this identifier to cite or link to this item: https://hdl.handle.net/20.500.12008/49965 How to cite
Title: Theoretical and in-situ FTIR study of the atmospheric sink of methyl dichloroacetate (MDCA) by OH radicals and Cl atoms : Kinetics, product distribution and mechanism
Authors: Straccia Cepeda, Vianni
Cardona, Alejandro L.
Blanco, María Belén
Ventura, Oscar N.
Teruel, Mariano A.
Type: Artículo
Keywords: Methyl dichloroacetate, Fourier transform infrared, Potential-Energy Surface, Volatile Organic Compounds, Atmospheric oxidants, Dicloroacetato de metilo, Infrarroja por Transformada de Fourier, Superficie de energía potencial, Compuestos orgánicos volátiles, Oxidantes atmosféricos
Issue Date: 2024
Abstract: The atmospheric degradation of methyl dichloroacetate can be initiated by •OH and Cl• radicals through H atom abstraction from the alkyl groups (Cl2HC– or –CH3) of the chloroester. Product yields for the gas-phase reaction with •OH were determined experimentally in a 480 L Pyrex glass atmospheric-simulation reactor coupled to an in situ Fourier transform infrared (FTIR) spectrometer. In addition to those results, we present in this paper a complete degradation mechanism based on thermodynamic data obtained by identifying all critical points on the potential-energy surface for these reactions, employing density functional calculations with the M06-2X and MN15 hybrid exchange–correlation functionals and the aug-cc-pVTZ basis sets. A conformational search for reactants and transition states was performed. The energies of these conformers were later corrected at the CCSD(T,Full)-F12/complete basis set level by using the SVECV-f12 composite method. The corrected energies were then used to obtain the theoretical rate coefficients in a multiconformer approach. The global rate coefficient calculated for the reaction of methyl dichloroacetate with •Cl atoms is (7.34 × 10–12 cm3 molecule–1·s–1), and the global rate coefficient calculated for the reaction with •OH radicals is (1.07 × 10–12 cm3 molecule–1·s–1). The identified products and their respective yield percentages for the reaction of MDCA with •OH were Cl2CHCOOH (44 ± 3%), COCl2 (43 ± 3%), and CO (41 ± 6%). The analysis of the mechanism suggests that formation of P1 (Cl2CO, phosgene) occurs mainly by abstraction from the Cl2HC– group since the formation of P4 (Cl2CHC(O)OH, dichloroacetic acid) and P5 (CO, carbon monoxide) is more favorable in the path for abstraction from the –OCH3 group. The multiconformer calculated rate constant values were compared with the values obtained employing only the low-lying TSs and with our own previous experimental studies. Branching ratios for the reaction with •Cl were compared to the experimental product yields.
Description: Postprint. La versión final fue publicada en: https://pubs.acs.org/doi/10.1021/acsearthspacechem.4c00264
Publisher: American Chemical Society
IN: ACS Earth and Space Chemistry, v.8, nº 12, 2024
Sponsors: Alexander von Humboldt Foundation
Agencia Nacional de Investigación e Innovación (Uruguay)
Consejo Superior de Investigaciones Científicas (Uruguay)
Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina)
Citation: Straccia Cepeda, V., Cardona, A., Blanco, M. y otros. "Theoretical and in-situ FTIR study of the atmospheric sink of methyl dichloroacetate (MDCA) by •OH radicals and Cl• atoms : Kinetics, product distribution and mechanism". [en línea] ACS Earth and Space Chemistry [en línea] v.8, nº 12, 2024. 34 p. DOI: 10.1021/acsearthspacechem.4c00264
License: Licencia Creative Commons Atribución - No Comercial - Sin Derivadas (CC - By-NC-ND 4.0)
Appears in Collections:Publicaciones académicas y científicas - Facultad de Química

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