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

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 Br empty set nsted acidic Ionic liquid (IL) N,N-Diethyl-1,4-phenylenediamine hydrogen sulfate, [DPhDA]HSO4 as a catalyst for the alpha-glucose dehydration to 5-HMF. Quantitative a-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 degrees C in 30 min (TOF 6.1 h(-1)). 3-fold increase in reaction time leads to higher (94%) 5-HMF yield at 160 degrees C 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 (Fig. 1)). Further computational mechanistic studies revealed the function of the catalytic sites in the alpha-glucose dehydration. We calculated five-membered ring formation and water extrusion in one concerted transition state (TS2A, Delta G double dagger = 38.8 kcal/mol) following the a-glucose ring-opening (TS1, Delta G double dagger = 20.4 kcal/mol). Further four steps (sp(3)-s, C-H bond cleavages (TS3, TS6) and dehydroxylation (TS4A, TS5)) are quite straightforward to reach the product (5-HMF). (C) 2021 Elsevier Ltd. All rights reserved.