Theoretical studies on the mechanisms and rate constants for the hydroxylation of n-butyl, iso-butyl and tert-butyl vinyl ethers in atmosphere

Atmospheric insight into the reaction mechanism and kinetics of isopropenyl methyl ether (i-PME) initiated by OH radicals and subsequent oxidation of product radicals

Studies on primary gas-phase reactions of emitted saturated and unsaturated ethers with oxidants and subsequent secondary reactions of product radicals with O₂ in the presence of NO are important in their atmospheric chemical processes. To accomplish these findings, we have examined the chemistry of OH-initiated oxidation of isopropenyl methyl ether (i-PME) CH₃C(CH₂)OCH₃ by electronic structure ca using density functional theory. Our energetic calculations show that OH additions to carbon-carbon double bonds of i-PME are more favorable reaction pathways than H-abstraction reactions from the various CH sites of the titled molecule. The rate constant values which are obtained from the transition state theory also signify that OH-addition reactions have faster reaction rates than H-abstraction reactions. Our calculated total rate constant of the reaction is found 9.90 × 10^-11 cm³ molecule^-1 s^-1. The percentage branching ratio calculations imply that OH-addition reactions have 98.09% contribution in the total rate constant. The atmospheric lifetime of i-PME is found to be 2.8 h. Further, we have identified 2-hydroxy-2-methoxypropanol, methyl acetate, methy-1,2-hydroxyacetate and 1-hydroxypropane-2-one, 1,2-dihydroxypropan-2-yl format, 2-hydroxyacetic acid, acetic acid, and formaldehyde from the secondary oxidation of product radicals.

Atmospheric degradation of 2-chloroethyl vinyl ether, allyl ether and allyl ethyl ether: Kinetics with OH radicals and UV photochemistry

Unsaturated ethers are oxygenated volatile organic compounds (OVOCs) emitted by anthropogenic sources. Potential removal processes in the troposphere are initiated by hydroxyl (OH) radicals and photochemistry. In this work, we report for the first time the rate coefficients of the gas-phase reaction with OH radicals (k_OH) of 2-chloroethyl vinyl ether (2ClEVE), allyl ether (AE), and allyl ethyl ether (AEE) as a function of temperature in the 263-358 K range, measured by the pulsed laser photolysis-laser induced fluorescence technique. No pressure dependence of k_OH was observed in the 50-500 Torr range in He as bath gas, while a slightly negative T-dependence was observed. The temperature dependent expressions for the rate coefficients determined in this work are: The estimated atmospheric lifetimes (τ_OH) assuming k_OH at 288 K were 3, 2, and 4 h for 2ClEVE, AE and AEE, respectively. The kinetic results are discussed in terms of the chemical structure of the unsaturated ethers by comparison with similar compounds. We also report ultraviolet (UV) and infrared (IR) absorption cross sections (σ_λ and σ(ν˜), respectively). We estimate the photolysis rate coefficients in the solar UV actinic region to be less than 10^-7 s^-1, implying that these compounds are not removed from the atmosphere by this process. In addition, from σ(ν˜) and τ_OH, the global warming potential of each unsaturated ether was calculated to be almost zero. A discussion on the atmospheric implications of the titled compounds is presented.