Izato Yu-Ichiro, Koshi Mitsuo, Miyake Atsumi
Institute of Advanced Sciences, Yokohama National University , 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan.
J Phys Chem B. 2017 May 4;121(17):4502-4511. doi: 10.1021/acs.jpcb.6b10546. Epub 2017 Apr 21.
This work examined the reaction pathways involved in the initial decomposition of aqueous hydroxylamine solutions via the overall reaction, 2NHOH → NH + HNO + HO, using quantum chemistry calculations incorporating solvent effects. Several possible decomposition mechanisms were identified and investigated: three neutral-neutral bimolecular, two water-catalyzed, one neutral trimolecular, two ion-neutral bimolecular, and one cation-catalyzed. Optimized structures for the reactants, products, and transition states were obtained at the ωB97XD/6-311++G(d,p)/SCRF = (solvent = water) level of theory, and the total electron energies of such structures were calculated at the CBS-QB3 level of theory. The cation-catalyzed reaction 2NHOH + NHOH → NH + HNO + HO + NHOH (maximum energy barrier (ΔE) = 53.6 kJ/mol) and the anion-neutral bimolecular reaction NHOH + NHO → NH + NO + HO (ΔE = 79.0 kJ/mol) were both found to be plausible candidates for the dominant step in the initial decomposition. The results of this study indicate that both acidic and basic conditions can affect the thermal stability of hydroxylamine in water.
本研究通过结合溶剂效应的量子化学计算，考察了羟胺水溶液初始分解反应过程中涉及的反应路径，该反应的总反应式为2NHOH → NH + HNO + HO。确定并研究了几种可能的分解机理：三种中性-中性双分子机理、两种水催化机理、一种中性三分子机理、两种离子-中性双分子机理和一种阳离子催化机理。在ωB97XD/6-311++G(d,p)/SCRF = (溶剂 = 水)理论水平下获得了反应物、产物和过渡态的优化结构，并在CBS-QB3理论水平下计算了这些结构的总电子能量。发现阳离子催化反应2NHOH + NHOH → NH + HNO + HO + NHOH（最大能垒(ΔE) = 53.6 kJ/mol）和阴离子-中性双分子反应NHOH + NHO → NH + NO + HO（ΔE = 79.0 kJ/mol）均可能是初始分解过程中主导步骤的候选反应。本研究结果表明，酸性和碱性条件均可影响羟胺在水中的热稳定性。
