Heterogeneous catalytic epimerization of d-glucose to d-mannose by a tin-organic framework

Abstract

Monosaccharide D-mannose (D-Man) is of great interest in the food and pharmaceutical industries as a low-calorie sweetener and precursor for D-mannitol and medicaments. Nowadays, large-scale production of D-Man remains challenging due to a lack of efficient chemo-catalytic processes using D-glucose (D-Glc) as educt. In this work, heterogeneous catalytic epimerization of D-Glc to D-Man by a tin-organic framework (Sn-OF-1) was achieved. The reaction kinetics were explored using both conventional methods and time-resolved operando MAS ¹³C NMR spectroscopy. Under optimized reaction conditions (100 °C, 5 wt% D-Glc, 20 mg(cat) g⁻¹(EtOH : H₂O)), epimerization yielded a 77 : 23 equilibrium mixture of D-Glc : D-Man after 1.5 h reaction time. Most D-Glc (ca. 73%) was recovered from the obtained mixture of saccharides by crystallization from EtOH : MeOH (4.7 : 1). The remaining mixture of D-Man and D-Glc was separated via adsorption on CaY zeolite, resulting in a stream containing D-Man at 70% purity.