A unique acid-base zinc complex for highly efficient and selective transformation of glucose to fructose/5-hydroxymethylfurfural

Highly efficient and selective isomerization of glucose to fructose remains a challenging target due to the limitation of traditional catalysts with single type of active sites. Herein, a novel zinc complex (Zn[MTA]_n) was prepared and found to be extremely efficient in the presence of Zn-N acid-base active pairs. The combination of catalyst characterization, experiments and density functional theory (DFT) calculations reveals that Lewis acidity of Zn sites on Zn[MTA]_n is effectively activated and enhanced to facilitate the adsorption of electron pair on the aldehyde group of glucose, in addition, the proton on C2 position of glucose is extracted more quickly by the basic N active sites on 3-methyl-1H-1,2,4-triazole (MTA) ligand adjacent to Zn site. Consequently, Zn[MTA]_n with acid-base bifunctional Zn-N active pairs provided an outstanding fructose yield with the highest selectivity among all heterogeneous catalytic systems to date. Furthermore, a cyclic conversion strategy was developed for the highly selective synthesis of 5-hydroxymethylfurfural (HMF) from glucose through fructose in a water/MIBK biphasic media. In each cycle, ∼45 % glucose was consumed to HMF with a minor loss of carbon balance, which is a valuable and referential approach for the industrial production of HMF from glucose.