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

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• 作者：Konrad Stemmler ; Wolfgang Mengon ; David J. Kinnison ; and J. Alistair Kerr
• 刊名：Environmental Science & Technology
• 出版年：1997
• 出版时间：May 1997
• 年：1997
• 卷：31
• 期：5
• 页码：1496 - 1504
• 全文大小：353K
• 年卷期：v.31,no.5(May 1997)
• ISSN：1520-5851

文摘

This type of study provides information on thereactionmechanism of the conversion of a substrate molecule, inthiscase a glycol ether, into its oxidation products underpolluted tropospheric conditions. Such detailedpathwaysfor the breakdown of the substrate molecule lead to thegeneration of photooxidants, mainly ozone, and areessentialinput data for computer modeling studies used to deriveozone-creating potentials of volatile organic compoundsreleased into the atmosphere. The products formed bythe hydroxyl radical-initiated oxidation of 2-butoxyethanol(C₄H₉OCH₂CH₂OH) have been investigated byirradiating syntheticair mixtures containing the substrate, methyl nitrite, andnitric oxide at ppm levels in a Teflon bag reactor at roomtemperature. The decay of reactant and the formationof products were monitored by gas chromatography and bymass spectrometry. The molar yields of the majorproducts(mol of product formed/mol of 2-butoxyethanol consumed)were as follows: butyl formate(HC(O)OCH₂CH₂CH₂CH₃),0.35 ± 0.11; ethylene glycol monoformate(HC(O)OCH₂CH₂OH), 0.39 ± 0.18; butoxyacetaldehyde(CH₃CH₂CH₂CH₂OCH₂C(O)H), 0.12 ± 0.09; 3-hydroxybutyl formate(HC(O)OCH₂CH₂CHOHCH₃), ~0.20; and propionaldehyde,~0.2-0.3.The yields of minor products were as follows:2-propyl-1,3-dioxolane(CH₃CH₂CH₂CHOCH₂CH₂O),0.025 ± 0.005; ethyleneglycol monobutyrate(CH₃CH₂CH₂C(O)OCH₂CH₂OH),~0.02-0.03; 2-hydroxybutyl formate(HC(O)OCH₂CHOHCH₂CH₃), ~0.05; acetaldehyde, <0.05; propyl nitrate, 0.038±0.018; and butyraldehyde, <0.011. The productdistributionis explained by a mechanism involving initial OH attackat the five -CH₂- groups in 2-butoxyethanol followed bythesubsequent reactions of the resulting alkyl and alkoxyradicals. The mechanism is analogous to that proposedfor2-ethoxyethanol (Stemmler et al. Environ. Sci.Technol.1996, 30, 3385-3391), in which the alkoxyradicals predominantly undergo decomposition reactions, but also includesisomerization reactions for the alkoxy radicals that arederived from the butyl side chain in 2-butoxyethanol.Theobserved products, in conjunction with the proposedmechanism, account for a total molar yield of about 1.1,indicating that all the main routes are accounted for inthedegradation of this hydroxy ether. Rate coefficientsatroom temperature for the reactions of OH radicals with butoxyacetaldehyde and 2-propyl-1,3-dioxolane have beendetermined to be 20.6 × 10^-12 and 10.8 ×10^-12 cm³molecule^-1s^-1, respectively, with error limits of about±40%, in eachcase.