OH Radical Initiated Photooxidation of 2-Ethoxyethanol under Laboratory Conditions Related to the Troposphere: Product Studies and Proposed Mechanism

摘要

The products formed by the hydroxyl radical-initiated oxidation of 2-ethoxyethanol (CH_3CH_2OCH_2CH_2OH) have been investigated by irradiating synthetic air mixtures containing the substrate, methyl nitrite, and nitric oxide at ppm levels in a Teflon bag reactor at room temperature. The decay of reactants and the formation of products were monitored by gas chro-matography and mass spectrometry. The major products ethyl formate [HC(O)OCH_2CH_3], ethylene glycol monoformate [HC(O)OCH_2CH_2OH], ethylene glycol monoacetate [CH_3C(O)OCH_2CH_2OH], and ethoxyacetal-dehyde [CH_3CH_2OCH_2C(O)H] give a quantitative mass balance with the decay of the substrate molecule. The yields of these products were 34 ± 10%, 36 ± 7%, 7.8 ± 2.4%, and 24 ± 13%, respectively, in terms of percent of 2-ethoxyethanol removed by the OH radical The product distribution is explained by a mechanism involving initial OH attack at the three CH_2 groups in 2-ethoxyethanol followed by the subsequent reactions of the resulting alkyl and alkoxy radicals. The decomposition reactions of the alkoxy radicals from 2-ethoxyethanol, which can take place either by C-C or C-O bond breaking, involve preferential C-C cleavage rather than C-O cleavage. Rate coefficients at room temperature for the reactions of OH radicals with ethoxyacetaldehyde and 2-methyl-1,3-dioxolane (CH_3CHOCH_2CH_2O, a minor product) have been determined to be 16.6 x 10~(-12) and 9.4 x 10~(-12) cm~3 molecule~(-1) s~(-1), respectively.