水溶液中未官能化硝酸烷基酯水解的反应机理,ACS Earth and Space Chemistry

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水溶液中未官能化硝酸烷基酯水解的反应机理
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2021-01-12 , DOI: 10.1021/acsearthspacechem.0c00253
Fatemeh Keshavarz ₁ , Joel A. Thornton ₂ , Hanna Vehkamäki ₁ , Theo Kurtén ₃

Affiliation

硝酸烷基酯（ANs）既是氮氧化物自由基的吸收源又是氮氧化物自由基的来源（NOx = NO + NO ₂）在大气中。它们的反应会影响氮循环和臭氧形成，进而影响空气质量和气候。ANs可以排放到大气中或以气相形式产生。无论哪种情况，它们都可以分配到水性气溶胶中，在那里它们可能会水解，产生高溶解性硝酸盐产物，并充当NOx的永久吸收剂。AN水解的动力学部分决定了AN对氮循环的贡献程度。但是，尚不清楚各种气溶胶中许多AN的动力学，并且关于酸度和碱度对水解过程的影响存在矛盾的论点。使用计算方法，本研究中提出了甲基，乙基，丙基和丁基的硝酸盐与OH反应的机制^-（羟基离子；碱性水解），水（中性水解）和H ₃ O ⁺（氢离子；酸性水解）。使用量子化学数据和过渡态理论，我们追踪pH对碱性，中性和酸性水解通道的贡献以及在宽pH范围内AN水解的速率系数的影响。我们的研究结果表明，碱水解（即与OH AN反应^-）是我们评估的反应方案中最动力学和热力学有利的反应。此外，将我们的动力学结果与实验数据进行比较表明，目前尚存在未知的酸性机制负责AN水解的酸性催化。

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Reaction Mechanisms Underlying Unfunctionalized Alkyl Nitrate Hydrolysis in Aqueous Aerosols

Alkyl nitrates (ANs) are both sinks and sources of nitrogen oxide radicals (NOx = NO + NO₂) in the atmosphere. Their reactions affect both the nitrogen cycle and ozone formation and therefore air quality and climate. ANs can be emitted to the atmosphere or produced in the gas phase. In either case, they can partition into aqueous aerosols, where they might undergo hydrolysis, producing highly soluble nitrate products, and act as a permanent sink for NOx. The kinetics of AN hydrolysis partly determines the extent of AN contribution to the nitrogen cycle. However, kinetics of many ANs in various aerosols is unknown, and there are conflicting arguments about the effect of acidity and basicity on the hydrolysis process. Using computational methods, this study proposes a mechanism for the reactions of methyl, ethyl, propyl, and butyl nitrates with OH^– (hydroxyl ion; basic hydrolysis), water (neutral hydrolysis), and H₃O⁺ (hydronium ion; acidic hydrolysis). Using quantum chemical data and transition state theory, we follow the effect of pH on the contribution of the basic, neutral, and acidic hydrolysis channels, and the rate coefficients of AN hydrolysis over a wide range of pH. Our results show that basic hydrolysis (i.e., AN reaction with OH^–) is the most kinetically and thermodynamically favorable reaction among our evaluated reaction schemes. Furthermore, comparison of our kinetics results with experimental data suggests that there is an as yet unknown acidic mechanism responsible for acidic catalysis of AN hydrolysis.

更新日期：2021-02-18

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