High Yield of L-Sorbose via D-Glucose Isomerization in Ethanol over a Bifunctional Titanium-Boron-Beta Zeolite

LM Ren and YX Xiao and R Bhattacharjee and JJ Wu and PY Tang and S Caratzoulas and CG Meng and Q Guo and M Tsapatsis, CHEMISTRY-A EUROPEAN JOURNAL, 30, e202402341 (2024).

DOI: 10.1002/chem.202402341

D-Glucose-to-L-sorbose isomerization on Lewis acidic zeolite is a highly attractive avenue for sorbose production. But the L-sorbose yield is limited by the competing D-glucose-to-D-fructose isomerization and reaction equilibrium. In this work, it is suggested that ethanol directs the glucose conformation for selective D-glucose-to-L-sorbose isomerization. It also reacts with the produced L-sorbose to form ethyl- sorboside, which allows the D-glucose-to-L-sorbose isomerization to proceed beyond the thermodynamic equilibrium limit. It is shown that a bifunctional zeolite Beta containing framework titanium (Ti) and boron (B) is a selective catalyst for this tandem reaction: Lewis acidic framework Ti catalyzes the D-glucose-to-L-sorbose isomerization via an intramolecular 5,1-hydride shift process as confirmed by isotopic tracing experiments followed by C-13-NMR, while weak Br & oslash;nsted acid framework B selectively promotes the sorbose ketalization with ethanol. A remarkably high yield of L-sorbose with a high fraction of sugar (>95 %: 27 % unreacted glucose, 11.4 % fructose, 57 % sorbose) was obtained after the mixture produced in ethanol was hydrolyzed.

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