大气中羟基引发的不饱和酯降解：287 - 313 K温度范围内的动力学
OH-initiated degradation of unsaturated esters in the atmosphere: kinetics in the temperature range of 287-313 K.
作者信息
Blanco María B, Bejan Iustinian, Barnes Ian, Wiesen Peter, Teruel Mariano A
机构信息
Instituto de Investigaciones en Fisicoquimica de Cordoba (I.N.F.I.Q.C.), Dpto. de Fisicoquimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Ciudad Universitaria, 5000 Cordoba, Argentina.
出版信息
J Phys Chem A. 2009 May 21;113(20):5958-65. doi: 10.1021/jp901755x.
The kinetics of the gas-phase reactions of hydroxyl radicals (OH) with methyl methacrylate (k(1)), butyl methacrylate (k(2)), butyl acrylate (k(3)), and vinyl acetate (k(4)) have been investigated for the first time as a function of temperature using the relative technique. The experiments were performed in a 1080 L quartz glass photoreactor over the temperature range (T = 287-313 K) at a total pressure of 760 +/- 10 Torr synthetic air using in situ FTIR absorption spectroscopy to monitor the concentration-time behaviors of reactants. OH radicals were produced by the 254 nm photolysis of hydrogen peroxide (H(2)O(2)). The following Arrhenius expressions (in units of cm(3) molecule(-1) s(-1)) adequately describe the measured rate coefficients as a function of temperature: k(1) = (1.97 +/- 0.95) x 10(-12) exp[(921 +/- 52)/T], k(2) = (1.65 +/- 1.05) x 10(-11) exp[(413 +/- 34)/T], k(3) = (4.4 +/- 2.5) x 10(-13) exp[(1117 +/- 105)/T], and k(4) = (4.06 +/- 2.02) x 10(-12) exp[(540 +/- 49)/T]. All of the rate coefficients display a negative temperature dependence and low pre-exponential factor, which supports an addition mechanism for the reactions involving reversible OH-adduct formation. The rate coefficients (in units of cm(3) molecule(-1) s(-1)) determined at room temperature (298 K) were as follows: k(1) = (4.30 +/- 0.98) x 10(-11), k(2) = (6.63 +/- 1.42) x 10(-11), k(3) = (2.17 +/- 0.48) x 10(-11), and k(4) = (2.48 +/- 0.61) x 10(-11). The results are compared with previous values of the rate coefficients reported in the literature, which were mainly measured at room temperature. The reactivity of the various unsaturated esters toward the OH radical is discussed in terms of structure activity relationships and parallels are drawn with the OH-radical activities of structurally similar compounds. Using the kinetic parameters determined in this work, residence times of the esters in the atmosphere with respect to their reaction with OH have been determined and are compared with other possible degradation pathways. Possible atmospheric implications of the various degradation pathways studied are discussed.
首次采用相对技术研究了羟基自由基（OH）与甲基丙烯酸甲酯（k(1)）、甲基丙烯酸丁酯（k(2)）、丙烯酸丁酯（k(3)）和醋酸乙烯酯（k(4)）的气相反应动力学随温度的变化。实验在1080 L石英玻璃光反应器中进行，温度范围为（T = 287 - 313 K），总压力为760 ± 10 Torr的合成空气中，使用原位傅里叶变换红外吸收光谱监测反应物的浓度-时间行为。OH自由基通过过氧化氢（H₂O₂）的254 nm光解产生。以下阿伦尼乌斯表达式（单位为cm³·分子⁻¹·s⁻¹）充分描述了测得的速率系数随温度的变化：k(1) = (1.97 ± 0.95) × 10⁻¹² exp[(921 ± 52)/T]，k(2) = (1.65 ± 1.05) × 10⁻¹¹ exp[(413 ± 34)/T]，k(3) = (4.4 ± 2.5) × 10⁻¹³ exp[(1117 ± 105)/T]，k(4) = (4.06 ± 2.02) × 10⁻¹² exp[(540 ± 49)/T]。所有速率系数均呈现负温度依赖性和低指前因子，这支持了涉及可逆OH - 加合物形成的反应的加成机理。在室温（298 K）下测定的速率系数（单位为cm³·分子⁻¹·s⁻¹）如下：k(1) = (4.30 ± 0.98) × 10⁻¹¹，k(2) = (6.63 ± 1.42) × 10⁻¹¹，k(3) = (2.17 ± 0.48) × 10⁻¹¹，k(4) = (2.48 ± 0.61) × 10⁻¹¹。将结果与文献中报道的速率系数先前值进行了比较，这些先前值主要是在室温下测量的。根据结构 - 活性关系讨论了各种不饱和酯对OH自由基的反应活性，并与结构相似化合物的OH自由基活性进行了比较。利用本工作中确定的动力学参数，确定了酯在大气中与OH反应的停留时间，并与其他可能的降解途径进行了比较。讨论了所研究的各种降解途径可能对大气产生的影响。
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