5-Hydroxymethylfurfural (HMF) is a key platform chemical that may be obtained from various cellulosic (biomass) derivatives. Previously, it has been shown that ionic liquids (ILs) facilitate the catalytic conversion of glucose into HMF. Herein, we demonstrate that the careful design of the IL cation leads to new ionic solvents that enhance the transformation of glucose and more complex carbohydrates into HMF significantly. In Situ NMR spectroscopy and computational modeling pinpoint the key interactions between the IL, catalyst, and substrate that account for the enhanced reactivities observed.
Charge-assisted hydrogen bonds (CAHBs) play critical roles in many systems from biology through to materials. In none of these areas has the role and function of CAHBs been explored satisfactorily because of the lack of data on the energy of CAHBs in the condensed phases. We have, for the first time, quantified three types of CAHBs in both the condensed and gas phases for 1-(2'-hydroxylethyl)-3-methylimidazolium acetate ([C2OHmim][OAc]). The energy of conventional OH···[OAc](-) CAHBs is ∼10 kcal·mol(-1), whereas nonconventional C(sp2)H···[OAc](-) and C(sp3)H···[OAc](-) CAHBs are weaker by ∼5-7 kcal·mol(-1). In the gas phase, the strength of the nonconventional CAHBs is doubled, whereas the conventional CAHBs are strengthened by <20%. The influence of cooperativity effects on the ability of the [OAc](-) anion to deprotonate the imidazolium cation is evaluated. The ability to quantify CAHBs in the condensed phase on the basis of easier accessible gas-phase estimates is highlighted.
Platform chemicals are usually derived from petrochemical feedstocks. A sustainable alternative commences with lignocellulosic biomass, a renewable feedstock, but one that is highly challenging to process. Ionic liquids (ILs) are able to solubilize biomass and, in the presence of catalysts, convert the biomass into useful platform chemicals. Herein, we demonstrate that mixtures of ILs are powerful systems for the selective catalytic transformation of cellulose into 5-hydroxymethylfurfural (HMF). Combining ILs with continuous HMF extraction into methyl-isobutyl ketone or 1,2-dimethoxyethane, which form a biphase with the IL mixture, allows the online separation of HMF in high yield. This one-step process is operated under relatively mild conditions and represents a significant step forward towards sustainable HMF production.
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