Task-Specific Organic Salts and Ionic Liquids Binary Mixtures: A Combination to Obtain 5-Hydroxymethylfurfural From Carbohydrates

Abstract

The increase in energy demand and depletion of fossil fuels are among major issues of modern society. Valorization and transformation of raw materials in products of industrial value represent a challenge. This justifies the growing interest of scientific research toward the identification of suitable media and methodologies able to pursue above goals, paying attention to matter of sustainability. On this subject, we studied sulfonic-acid functionalized diimidazolium salts as catalysts for the conversion of fructose and sucrose to 5-hydroxymethylfurfural (5-HMF) in an ionic liquid mixture. In general, using these salts allowed us to obtain 5-HMF in good yields from both substrates in mild conditions. Indeed, at 60°C and in the presence of 20 mol% of catalyst, 5-HMF yields of 60 and 30% were obtained from fructose and sucrose, respectively. The catalytic system was recycled and used up to six times observing no appreciable loss in yield for the first four cycles. Moreover, we gathered mechanistic information by in situ 1 H NMR monitoring the dehydration of fructose. To dissect the role of acidity on the reaction, we determined the Hammett acidity function of each salt. Comparison of these results with yields and reactivity observed in the presence of related monocationic salts and with a dicationic salt bearing only one sulfonic acid group, allowed stating that the reactivity observed is the result of the combined action of acidity and structural features of the catalysts. Overall, the approach proposed here could contribute to pave the way to increase sustainability in the raw material valorization processes.

When Functionalization Becomes Useful: Ionic Liquids with a “Sweet” Appended Moiety Demonstrate Drastically Reduced Toxicological Effects

“…Their high thermal stability, low vapor pressure and flammability favoured their application as solvents, 2 catalysts, 3 and reagents. 4 As more applications of ILs appear, there is also a growing attention to their biodegradability and toxicity.…”

Continuous‐Flow Synthesis of 5‐Hydroxymethylfurfural, Furfural from Monosaccharides: A Simple, Fast, and Practical Method

“…The rate formation of HMF increases 40 times with Brønsted acidic ionic liquid, presumably because the good diffusion of Brønsted acidic ionic liquid into the reaction mixture enhances the dehydration reaction rate. D'Anna and coworkers reported the use of Amberlyst‐15 in [BMIM][BF 4 ] [31] or sulfonic‐acid functionalized diimidazoliumsalts [34] for the dehydration of fructose to produce HMF in high yield under conventional heating. Although the HMF was obtained in a lower yield than these reported methods, the fact that the reaction can reach completion within a short reaction time (only 45 s) makes the present method comparative regarding practicability to others in the literature.…”

“…[29][30][31] Recently, it is also reported that ionic liquids can enhance the rate of formation of HMF from fructose. [22,[32][33][34] Additionally, ionic liquids have been shown to be effective in the synthesis of HMF using ionic liquid/organic solvent as a biphasic system. [35][36][37][38] Although interesting results could be obtained, the large-scale industrial feasibility of these approaches is limited.…”

“…They have been promising solvents for biomass pretreatment and conversion due to their unique properties, such as negligible volatility, a wide range of liquid existence, high dissolution rates, excellent thermal stability, possible tailoring, and recyclability, they have been defined as green solvents for biomass pretreatment and conversion [29–31] . Recently, it is also reported that ionic liquids can enhance the rate of formation of HMF from fructose [22,32–34] . Additionally, ionic liquids have been shown to be effective in the synthesis of HMF using ionic liquid/organic solvent as a biphasic system [35–38] .…”

Dicationic stilbazolium salts: Structural, thermal, optical, and ionic conduction properties

“…In general, multi-charged ILs have been shown to have a greater range of physical properties than their monocationic counterparts, such as higher density, glass transition, melting point, surface tension, and shear viscosity [25]. Like traditional ILs, they can be task-specific ionic liquids depending on their chemical structures [26], [27], [28], [29], [30], [31], [32], [33], [34]. Notable recent examples include tetracationic acidic organic salt based on 1,4-diazabicyclo [2], [2], [2]octane (DABCO) that are used as catalyst in the Knoevenagel condensation reactions in water [29], [30].…”