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

流动式高温高压核磁共振探头的研制及亚临界和超临界水中化学反应的澄清

基本信息

批准号：
15350011
负责人：
KAJIMOTO Okitsugu
金额：
$ 9.22万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

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

本研究的目的是澄清在亚和超临界水中的有机反应的机制，通过一个新开发的高温高压流动核磁共振探针。本研究的第一部分是研制一种具有样品管、流路以及它们之间连接的探头，该探头应能承受高达500℃和50 MPa的压力。特别是，通过流线的温度控制是不可避免的重要性，正确确定的反应速率常数。我们设计了一个温度控制系统，沿流线有三个加热器沿着。此外，对于化学位移与水信号重叠的产物和反应物的峰面积的定量测定，应抑制H_2O的1H大信号。对于抑制，我们使用二项式序列脉冲方法，其能够将水1H信号抑制400倍。 ...更多信息 R探针，首次测定了亚临界水中Claisen重排反应的一级速率常数。烯丙基苯基醚（APE）在不同温度下的一级还原曲线中的直线给出了重排反应的速率常数。在270-310℃范围内，求得反应活化能为25.5 kJ mol ~（-1）。根据硝基乙烷的减少以及CH_3CHO、CH_3COOH和CH_3CONH_2的时间依赖性，确定了反应速率常数，并阐明了反应机理。还检测到反应中间体硝基乙烷和N-羟基乙酰胺。这些观察表明硝基乙烷分解的三种途径。其主要途径是通过硝基乙烷生成CH_3CHO（Nef反应）。第二条分解途径经N-羟基乙酰胺生成CH_3COOH和CH_3CONH_2，第三条分解途径可能经自由基中间体直接由硝基乙烷生成CH_3CN。第三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开发的高温高压流动NMR探针使我们能够确定亚临界温度和超临界温度下发生的化学反应的速率常数并阐明反应机理。少