2002 Fiscal Year Final Research Report Summary
Mechanisms of Noncatalytic Organic Chemical Reactions in Super- and Subcritical Water
| Project/Area Number |
13440179
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical chemistry
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
NAKAHARA Masaru Institute for Chemical Research, Professor, 化学研究所, 教授 (20025480)
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| Co-Investigator(Kenkyū-buntansha) |
WAKAI Chihiro Institute for Chemical Research, instructor, 化学研究所, 助手 (40293948)
OKAMURA Emiko Institute for Chemical Research, Instructor, 化学研究所, 助手 (00160705)
MATUBAYASI Nobuyuki Institute for Chemical Research, Instructor, 化学研究所, 助手 (20281107)
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| Project Period (FY) |
2001 – 2002
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| Keywords | supercritical water / subcritical water / noncatalytic reaction / NMR spectroscopy / hvdration / acid-catalyzed reaction / ether / Cannizzaro reaction |
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| Research Abstract |
Noncatalytic reactions at hydrothermal conditions are investigated systematically. It is well recognized recently that without adding any catalysts from outside, hot water induces a chemical reaction that proceeds at ambient conditions in the presence of a strong acid or base. A widespread explanation to the noncatalytic reactivity in water at hydrothermal conditions is that the reaction is catalyzed by the increased concentration of H^+ or OH^- due to the enhanced ionization constant of water. Our point is to kinetically prove that the undissociated form of water is responsible for the noncatalytic reactivity of high-temperature water. By focusing on a simple reaction involving ether bonding, we determine the rate constant for the reaction path induced by the undissociated form of water. The water-induced and acid-catalyzed rate constants are separately determined for the dehydration of 1,4-butanediol by varying the oxonium ion (H^+) concentration. It is found on the kinetic level over a wide range of temperature from moderate to supercritical that the undissociated form of water promotes the reaction at an effective acid concentration of 10^<-4>-10^<+6> M. The reaction of aldehyde was further investigated. In supercritical water at 400℃ and 0.5 g/cm^3 (37 Mpa), acetaldehyde was found to be transformed without catalysts into ethanol and acetic acid through a Cannizzarotype disproportionation reaction. No aldol-type condensation products were detected, and the disproportionation competed with the decomposition into methane. Ethanol was generated in excess to acetic acid, and carbon dioxide appeared as a product only in the presence of supercritical water. This reaction behavior is explained by considering that carbon monoxide is provided by the acetaldehyde decomposition and leads to the formation of formic acid as a reducing intermediate for acetaldehyde.
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