Stannate-catalysed glucose-fructose isomerisation in alcohols

Isomerisation of glucose to fructose is a crucial step in the valorisation of biomass-derived carbohydrates to renewable chemicals, polymers, and fuels. Glucose isomerisation is base-catalysed but superior catalytic activity can be obtained with Lewis acidic materials such as Sn-beta zeolite, where partially hydrolysed framework Sn-sites, Sn-(OH)(x), are considered the catalytically active sites. Alkali-metal stannate salts (MxSnO3 center dot 3H(2)O) contain a similar type of Sn-(OH)(x) sites in the form of [Sn(OH)(6)](2-) complex anions. In this work, we report the use of M2SnO3 center dot 3H(2)O (M = Na, K) as effective catalysts for glucose-fructose isomerisation in alcohols. Isotope-labelling experiments and kinetic studies demonstrated that the isomerisation with Na2SnO3 center dot 3H(2)O proceeded in methanol by base-catalysis via a proton-transfer mechanism with a low activation energy (63.5 +/- 7.0 kJ mol(-1)). This allowed the stannate to facilitate a higher fructose yield and a higher fructose selectivity than Sn-beta within a shorter reaction time at a lower reaction temperature. Furthermore, in isopropanol and higher alcohols where the stannates are insoluble the reaction proceeded heterogeneously, thus suggesting the catalytic system to be a green and viable alternative to other soluble catalyst systems.

Automated summary

Isomerisation of glucose to fructose is a crucial step in the valorisation of biomass-derived carbohydrates to renewable chemicals, polymers, and fuels. This study demonstrated the use of alkali-metal stannate salts as effective catalysts for glucose-fructose isomerisation in alcohols, resulting in higher fructose yield and selectivity than traditional catalysts. The reaction proceeded either by base-catalysis or heterogeneously, depending on the solubility of the stannates in the alcohol medium.