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

The products formed by the hydroxyl radical-initiated oxidation of 2-ethoxyethanol (CH 3 CH 2 OCH 2 CH 2 OH) 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 2 CH 3 ], ethylene glycol monoformate [HC(O)OCH 2 CH 2 OH], ethylene glycol monoacetate [CH 3 C(O)OCH 2 CH 2 OH], and ethoxyacetaldehyde [CH 3 CH 2 OCH 2 C(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 reac tions 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 3 CHOCH 2 CH 2 O, a minor product) have been determined to be 16.6 × 10 - 12 and 9.4 × 10 - 12 cm 3 molecule - 1 s - 1, respectively.