Mannose, fructose and glucose were treated in subcritical water at "*ῌC, and the disappearance of each substrate and formation of other hexoses were observed at various residence times in a tubular reactor. Isomerization of mannose to fructose occurred most frequently, followed by mannose to glucose ; no isomerization of glucose to mannose was observed. The temperature dependencies of mannose disappearance, the isomerization of mannose to fructose and glucose, and the resulting degradation of

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... e produced fructose and glucose were observed in the range of +2* to ,.*ῌC. The activation energy and frequency factor for each process were evaluated according to the Arrhenius equation, and it was found that the enthalpy-entropy compensation for the processes was maintained.