What is it about?
An intermediate called Criegee intermediate generally forms in the gas phase ozonolysis of the alkenes, which is very important in the atmospheric regime. This study determines the kinetics of one of these intermediates (CH2OO) with a ketone (methyl-ethyl ketone, CH3COC2H5) relevant to Earth's atmosphere.
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Why is it important?
The short-lived Criegee intermediates react with atmospheric VOCs and get isomerised into carboxylic acids. They also convert the low molecular weight VOCs into low volatile oxygenated compounds by getting inserted, ultimately generating precursors for the secondary organic aerosol, and hence directly affecting the air quality. Criegee intermediates, during their unimolecular decomposition, release OH radicals, which are the most dominant oxidant in the atmosphere and are also known as the detergent of the atmosphere. Hence, to model the reaction of Criegee intermediates, the rate coefficients measurement of the Criegee intermediates with known VOCs is very important. Methyl-ethyl ketone is one such VOC, which has not yet been explored.
Perspectives
The gas-phase kinetics of the reaction of CH2OO with MEK was investigated by employing a custom-built PLP-CRDS technique in the temperature range 258–318 K. A negative T-dependency of kinetics was observed in the studied range, which was further confirmed by theoretical calculations at CCSD(T)/aug-cc-pVTZ//B3LYP/6-311G(d,p) level of theory. A detailed reaction mechanism was proposed for the same, revealing the formation of SOZ in the primary entrance channel. The decomposition and isomerization pathways were compared using thermodynamic and kinetic parameters, and HCOOH and MEK were found to be the major products.
Amit Debnath
Indian Institute of Technology Madras
Read the Original
This page is a summary of: Investigation of kinetics and mechanistic insights of the reaction of criegee intermediate (CH2OO) with methyl-ethyl ketone (MEK) under tropospherically relevant conditions, Chemosphere, January 2023, Elsevier,
DOI: 10.1016/j.chemosphere.2022.137217.
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