Development of flow-type high-temperature and high-pressure NMR probe and clarification of chemical reactions in sub-and supercritical water

本研究旨在用新研制的高温高压流通式核磁共振探头阐明亚临界和超临界水中的有机反应机理。本研究的第一部分是研制具有样品管、流线和它们之间的连接的探头，它们之间的连接应可承受高达500℃和50 Mpa。特别是，通过流线的温度控制对于正确确定反应的速率常数是必不可少的。我们设计了一套沿流水线有三个加热器的温度控制系统。此外，为了定量测定化学位移与水信号重叠的产物和反应物的峰面积，应抑制H2O的大1H信号。在抑制方面，我们使用了二项式序列脉冲法，使水的1H信号抑制了400倍。通过对NM…的上述改进更多的R探针，我们首次测定了亚临界水中Claisen重排的一级速率常数。不同温度下烯丙基苯基醚(APE)还原的一级曲线给出了重排反应的速率常数。在2 70~310℃温度范围内测得反应的活化能为2 5.5kJmol-1，并用该探针研究了亚超临界水中硝基乙烷的分解反应.考察了硝乙烷的还原以及CH3CHO、CH3COOH和CH3CONH2的时间依赖性，确定了反应的速率常数，并阐明了反应机理。还检测了反应中间体ACI-硝乙烷和N-羟基乙酰胺。这些观察揭示了硝乙烷分解的三条途径。主要途径是通过ACI-硝乙烷(Nef反应)生成CH3CHO。第二个分解途径通过N-羟基乙酰胺生成CH3COOH和CH3CONH2，第三个次要途径可能通过自由基中间体直接从硝乙烷生成CH3CN。第三条路径的贡献随着温度的升高而增加。因此，我们成功地证明了所研制的高温高压流动核磁共振探针使我们能够确定发生在亚临界和超临界温度下的化学反应的速率常数，并阐明了反应机理。较少

The present research aims at the clarification of the mechanism of organic reactions in sub-and supercritical water by a newly developed high-temperature and high-pressure flow-through NMR probe. The first part of this research was the development of the probe equipped with a sample tube, flow line and the connections between them which should be endurable up to 500℃ and 50 MPa. In particular, the temperature control through the flow line was of inevitable importance for the correct determination of the rate constants of the reactions. We devised a temperature controlling system with three heaters along the flow line. Further, the large 1H signal of H_2O should be suppressed for the quantitative determination of the peak areas of the products and reactants whose chemical shifts were overlapped with the water signal. For the suppression, we used the binomial sequence pulse method which enabled the suppression of the water 1H signal by a factor of 400.With the above improvement to the NM … More R probe, we first determined the 1st-order rate constants of the Claisen rearrangement in subcritical water. The straight lines in the 1st-order plots for the decrease of allyl phenyl ether (APE) at several temperatures gave the rate constants of the rearrangement. The activation energy was evaluated to be 25.5 kJ mol-1 in the temperature range of 270-310℃.The decomposition of nitroethane in sub-and supercritical water was then investigated with the probe. The decrease of nitroethane as well as the time dependence of CH_3CHO, CH_3COOH, and CH_3CONH_2 was followed to determine the rate constants and elucidate the reaction mechanism. The reaction intermediates, aci-nitroethane and N-hydroxyacetamide were also detected. These observation indicated the three pathways of the nitroethane decomposition. The major pathway is the formation of CH_3CHO via aci-nitroethane (Nef reaction). The second decomposition pathway forms CH_3COOH, and CH_3CONH_2 via N-hydroxyacetamide and the third minor path generates CH_3CN directly from nitroethane, probably via a radical intermediate. The contribution of the 3rd path increases with increasing temperature.Thus, we successfully demonstrated that the developed high-temperature and high-pressure flow-NMR probe enabled us to determine the rate constants and clarify the reaction mechanism for the chemical reactions occurring in sub-and supercritical temperature. Less