(410e) Sn-Beta in the Presence of Inorganic Promoters Induces the Epimerization of Aldoses in Water Via a Carbon-Shift Mechanism

Here we shown that Sn-Beta zeolite in the presence of specific inorganic promoters catalyzes the selective epimerization of aldoses in aqueous media.  The reaction mechanism, investigated using 13C-labeled sugars and NMR, involves a carbon-shift whereby C1 forms a new C-C bond with C3, while C2 moves to the C1 position. In the absence of promoters, Sn-Beta catalyzes a regular isomerization of glucose to fructose via an intramolecular hydride shift.  The relative ratio of isomerization to epimerization can be controlled by the ratio of glucose to promoter.  The epimerization is demonstrated for other aldoses such as xylose and arabinose and other zeolites containing Lewis acid centers (e.g., Ti-Beta) indicating this may be a general cooperative effect.  This work provides a more general method of performing  epimerizations than currently available routes, such as the Bilik reaction and Ca-mediated epimerizations. The reaction has applications in the production of polyols, artificial sweeteners, pharmaceuticals, fuels and isotopically enriched sugars.