Aqueous Isomerization of Glucose to Fructose Catalyzed by Guanidinium Ionic Liquids

Abstract

The isomerization of glucose to fructose is the rate determining step in many techniques for chemo‐catalytic conversion of cellulosic biomass to highly value‐added biochemicals. However, current techniques are generally challenging by poor process efficiency, low fructose yield and selectivity, etc. Therefore, the exploitations of novel catalytic systems for the efficient isomerization of glucose are important and highly desired. Herein, a series of biodegradable guanidinium ionic liquids were synthesized and employed in the selective isomerization of glucose to fructose. The results demonstrated that the performance of the isomerization of glucose was significantly influenced by the basic strength of the ionic liquids and the reaction conditions involving catalyst dosage, reaction temperature, time, and solvent. At the optimized conditions of 80 °C for 30 min, an impressive fructose yield of 34.1 % could be obtained in the presence of tetra methyl guanidinium proline ([TMG]Pro). Furthermore, the kinetic behavior of the process was further studied, and the apparent activation energy was 57±2 KJ/mol, which is lower than most current base‐catalyzed glucose isomerization systems. Moreover, the results of isotope labeling experiments showed that this aqueous isomerization of glucose was proceeded via a deprotonation mechanism. Therefore, this work provides a new insight on the selective isomerization of glucose.

Toward Understanding Base-Catalyzed Isomerization of Saccharides

“…The induction time was observed for a number of soluble catalysts including KOH, 19 NaOH, 22 phosphate buffer, 64 amines, 45,91 and guanidinium ionic liquids. 92 At conversions of 20−30%, a maximum selectivity for Fru is attained; at higher conversions, selectivity decreases due to decomposition. The selectivity− conversion curves present thus volcano-shaped plots.…”

“…Under the reaction conditions, enediolates are prone to degradation processes, leading to low selectivity, as described in Section . The induction time was observed for a number of soluble catalysts including KOH, NaOH, phosphate buffer, amines, , and guanidinium ionic liquids . At conversions of 20–30%, a maximum selectivity for Fru is attained; at higher conversions, selectivity decreases due to decomposition.…”

The Synthesis of Nitrogen- and Oxygen-Containing Heterocyclic Scaffolds Assisted by Ionic Liquids: A 2022 Literature Survey

“…Long et al have investigated the application of guanidium-based ILs in the successful chemo-catalytic isomerization of glucose (66) into fructose (67) (Scheme 19). 76 A total of fourteen guanidinium based ILs were synthesized and screened for the conversion of 66 into 67. It was found that the basic strength of the ionic liquid, along with its catalytic amount, reaction temperature, reaction time, and solvent played key roles in the formation of 67, where the highest yield (34%) was obtained upon the treatment of 66 with tetramethyl guanidinium proline [TMG][Pro] at 80 °C for 30 minutes in H 2 O.…”

Selective isomerization of α-pinene oxide totrans-carveol by task-specific ionic liquids: mechanistic insightsviaphysicochemical studies

“…It has been noticed that basic ILs composed of [N 4,4,4,4 ]Pro (tetrabutyl ammonium proline) and [TMG]Pro (tetramethyl guanidinium proline) have the tendency to efficiently isomerize glucose into fructose. 18,19 Likewise, the catalytic conversion of n -hexane to the corresponding branching isomers with a low conversion yield of 11.52% to 36.30% has been observed with three distinct imidazolium and pyridinium-based chloroaluminate ILs. 20 IL-supported metal complexes for the isomerization reactions can be seen in various reports.…”