Unveiling the catalytic effects of Brønsted acidic ionic liquid on quantitative α-glucose conversion to 5-HMF: Experimental and computational studies

Abstract Effective biomass conversion to 5-HMF(5-hydroxymethylfurfural) is still a challenge and needs to be improved because of the 5-HMF importance as building blocks for valuable monomers and fuel precursors. We suggest for the first time utilization of low-cost metal-free Bronsted acidic Ionic liquid (IL) N,N-Diethyl-1,4-phenylenediamine hydrogen sulfate, [DPhDA]HSO4 as a catalyst for the α-glucose dehydration to 5-HMF. Quantitative α-glucose conversion is achieved via optimizing the reaction condition: 91.4 % 5-HMF yield with 30 mol% [DPhDA]HSO4 in the presence of DMSO as a solvent at 160 oC in 30 minutes (TOF 6.1 h-1). 3-fold increase in reaction time leads to higher (94%) 5-HMF yield at 160 oC with lower TOF 1.6 h-1. The IL surprising catalytic performance is scrutinized with its amphiprotic nature (availability of basic and acidic spots in its structure ( Figure 1 . Further computational mechanistic studies revealed the function of the catalytic sites in the α-glucose dehydration. We calculated five-membered ring formation and water extrusion in one concerted transition state (TS2A, ΔG‡=38.8 kcal/mol) following the α-glucose ring-opening (TS1, ΔG‡=20.4 kcal/mol). Further four steps (sp3-s, C-H bond cleavages (TS3, TS6) and dehydroxylation (TS4A, TS5)) are quite straightforward to reach the product (5-HMF).