Rate constants for the OH reactions with oxygenated organic compounds in aqueous solution

Abstract

AbstractThe kinetics of the oxidation of functionalized organic compounds of atmospheric relevance by the hydroxyl radical (OH) was measured in the aqueous phase. Competition kinetics, using the thiocyanate anion (SCN−) as competitor, was applied using both a laser flash photolysis long path absorption (LP‐LPA) setup and a Teflon AF waveguide photolysis (WP) system. Both experiments were intercompared and validated by measuring the rate coefficients for the reaction between OH and acetone where values of k1 = (1.8 ± 0.4) × 108 M−1 s−1 were obtained with the WP system, which agrees very well with the rate constant of k1 = (2.1 ± 0.6) × 108 M−1 s−1 determined before by LP‐LPLA [1]. The following temperature dependencies of the rate constants (M−1 s−1) for the reactions of OH with ketones, dicarboxylic acids, and unsaturated compounds were obtained in Arrhenius' form: Reaction of OH with: methylisobutyl ketone (MIBK): k2 = (1.0 ± 0.1) × 1012 magnified image, N‐methyl pyrrolidone (NMP): k3 = (1.8 ± 0.2) × 1011 exp magnified image, malic acid (pH = 1): k4 = (7.9 ± 0.8) × 1010 magnified image, maleate monoanion (pH = 4.3): k5 = (2.9 ± 0.4) × 1011 magnified image, maleate dianion (pH = 9): k6 = (1.2 ± 0.2) × 1011 magnified image, mesoxalic acid (pH = 1): k7 = (3.8 ± 0.8) × 1010 magnified image, triethyleneglycol divinyl ether (DVE‐3): k9 = (2.3 ± 0.1) × 1013 magnified image methacrolein: k10 = (3.0 ± 0.1) × 1013 magnified image. The Ea/A values are given with full precision to avoid rounding errors. Equations were derived from the regression line of the Evans‐‐Polanyi plot in the form activation energy (Ea) versus bond dissociation energy (BDE) and from the regression line for the region 380 ⩽ BDE ⩽ 412 kJ mol−1 of the Evans–Polanyi plot in the form log kH versus BDE. Both equations can be used as a tool for predicting unknown rate coefficients and activation energy for the reactions of OH with different organics in the aqueous phase. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 309–326, 2009