While the catalytic conversion of
glucose to
5-hydroxymethyl furfural (HMF) catalyzed by SO3H-functioned
ionic liquids (ILs) has been achieved successfully, the relevant molecular mechanism is still not understood well. Choosing
1-butyl-3-methylimidazolium chloride [C4SO3HmimCl] as a representative of SO3H-functioned IL, this work presents a density functional theory (DFT) study on the catalytic mechanism for conversion of
glucose into HMF. It is found that the conversion may proceed via two potential pathways and that throughout most of elementary steps, the
cation of the IL plays a substantial role, functioning as a
proton shuttle to promote the reaction. The
chloride anion interacts with the substrate and the acidic
proton in the imidazolium ring via H-bonding, as well as provides a polar environment together with the imidazolium
cation to stabilize intermediates and transition states. The calculated overall barriers of the catalytic conversion along two potential pathways are 32.9 and 31.0 kcal/mol, respectively, which are compatible with the observed catalytic performance of the IL under mild conditions (100 °C). The present results provide help for rationalizing the effective conversion of
glucose to HMF catalyzed by SO3H-functionalized ILs and for designing IL catalysts used in biomass conversion chemistry.