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-e thoxyethanol (CH3CH2OCH2CH2OH) have been investigated by irradiating s ynthetic air mixtures containing the substrate, methyl nitrite, and ni tric 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 chromatography and mass spectrometry. The major products ethyl fo rmate [HC(O)OCH2CH3], ethylene glycol monoformate [HC(O)OCH2CH2OH], et hylene glycol monoacetate [CH3C(O)OCH2CH2OH], and ethoxyacetaldehyde [ CH3CH2OCH2C(O)H] give a quantitative mass balance with the decay of th e substrate molecule. The yields of these products were 34 +/- 10%, 36 +/- 7%, 7.8 +/- 2.4%, and 24 +/- 13%, respectively, in terms of perce nt of 2-ethoxyethanol removed by the OH radical. The product distribut ion is explained by a mechanism involving initial OH attack at the thr ee CH2 groups in 2-ethoxyethanol followed by the subsequent reactions of the resulting alkyl and alkoxy radicals. The decomposition reaction s of the alkoxy radicals from 2-ethoxyethanol, which can take place ei ther by C-C or C-O bond breaking, involve preferential C-C cleavage ra ther than C-O cleavage. Rate coefficients at room temperature for the reactions of OH radicals with ethoxyacetaldehyde and 2-methyl-1,3-diox olane (CH3CHOCH2CH2O, 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.