Rate constants for reaction of hydroxyl radicals with acetates and glycols in the gas phase.
Rate consts. for the gas phase reaction of OH radicals with AcOBu (I), 2-ethoxyethanol (II), 2-butyoxyethanol (III), and 1-acetyoxy-2-ethoxyethane (IV) at 298-500 K were measured using a combined laser photolysis/resonance fluorescence technique. The rate consts. at 298 K were analyzed in terms of individual C-H bond contributions using estd. thermochem. data and empirical group reactivity correlations. The primary reaction was dominated in all cases by H abstraction from a CH2 group with the abs. reactivity depending on the a-substituent and decreasing in the order -OCH2- > HOCH2- > -CH2CH2- .apprx. MeCH2- > -C(O)OCH2-. Based on these findings and on generally accepted oxidn. schemes, a simplified mechanism is suggested for the atm. degrdn. of glycols. Assuming an av. tropospheric OH concn. of 5 * 105/cm3, the atm. lifetimes are 5.5 and 1.7 days for I and II, III, and IV, resp.
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