Elsevier

Catalysis Communications

Volume 9, Issue 6, 31 March 2008, Pages 1383-1388
Catalysis Communications

Preparation of 5-hydroymethylfurfural by dehydration of fructose in the presence of acidic ionic liquid

https://doi.org/10.1016/j.catcom.2007.12.002Get rights and content

Abstract

In this paper, preparations of 5-hydroymethylfurfural (HMF) by the dehydration of fructose in the presence of the Brønsted acidic ionic liquid, 3-allyl-1-(4-sulfobutyl)imidazolium trifluoromethanesulfonate, as well as its Lewis acid derivative, 3-allyl-1-(4-sulfurylchloride butyl)imidazolium trifluoromethanesulfonate, were investigated. It was concluded that the type of acidic ionic liquid used played a significant role in the reaction, and the Lewis acidic ionic liquid acts more effectively than its Brønsted acidic counterpart. By means of UV–visible spectroscopy, the acidities of both kinds of ionic liquids were characterized, together with an effort to correlate the relationship between acidity and activity. Moreover, it was demonstrated that when these acidic ionic liquids were immobilized on silica gel, they can be used as effective and reusable solid catalysts for the dehydration reaction of fructose to HMF, offering much better performances for the title reaction than sulfuric acid and sulfonylchloride modified silica gels in terms of activity and reusability.

Introduction

Preparation of 5-hydroymethylfurfural (HMF) through the dehydration reaction of sugars is one of the most important approaches to transform biomass to useful chemicals, as HMF and its derivatives have been recognized as promising surrogates for petroleum-based chemicals [1]. For example, HMF is known as a potential biofuel and one of its oxidative derivatives, 2,5-furandicarboxylic acid, may replace terephthalic acid as a monomer in the production of plastics. Therefore, though studies on the dehydration of hexose to HMF have taken place over many years, new efforts towards an efficient and easy-to-use process for the preparation of HMF are ongoing, particularly in the context of the increasing demands for alternative energy sources [2].

Meanwhile, ionic liquids, viewed by some as a sort of novel reaction medium, have gained a variety of applications in synthetic chemistry over the past few years [3]. Studies involving the utilization of ionic liquids as a reaction medium or as catalysts for the dehydration reaction of hexose to HMF have also been reported. For example, Moreau et al., have demonstrated that neutral ionic liquids such as [BMIm]PF6 and [BMIm]BF4 can act as a suitable reaction medium for the dehydration of fructose to HMF in the presence of the acidic catalyst, Amberlyst-15 [4]. A Brønsted acidic ionic liquid, 1-H-3-methyl imidazolium chloride, was also used as both solvent and catalyst for the dehydration of fructose and sucrose [5]. Recently, metal chlorides in the neutral ionic liquid [EMIm]Cl have been found to be effective catalysts for converting sugars such as fructose and glucose to HMF. These results suggest that ionic liquids as solvents or catalysts can play a positive role in the development of effective processes for the dehydration of hexose to HMF [2a]. Unfortunately to date, researchers are still far from a sufficient understanding of the details and merits of ionic liquids as a reaction medium or as catalysts for the dehydration reaction of hexose to HMF; therefore, more studies are still needed with this regard.

Recently, we have reported that another kind of Brønsted acidic ionic liquid, 3-allyl-1-(4-sulfobutyl)imidazolium trifluoromethanesulfonate ([ASBI][Tf]) and its Lewis acid derivative, 3-allyl-1(4-sulfurylchloride butyl)imidazolium trifluoromethanesulfonate ([ASCBI][Tf]), can be used as catalysts for reactions such as nitration, alkylation, and the Koch reaction [6]. When these acidic ionic liquids are immobilized on silica gel (ILIS), they can also be used as effective and reusable solid catalysts for esterfication and indole condensation reactions [6], [7]. As an extension of our ongoing studies of these acidic ionic liquids, we report herein their application as catalysts for the dehydration of fructose to HMF using microwave irradiation, together with an effort to characterize both kinds of ionic liquids using UV–visible spectroscopy. This characterization revealed that the type of acidity of the ionic liquids played a significant role in the efficiency of the reaction Scheme 1. Moreover, in comparison with the analogous solid acidic catalysts such as sulfuric acid and sulfonylchloride modified silica gels, acidic ionic liquids immobilized on silica gel can afford better activity and reusability for the dehydration of fructose to HMF.

Section snippets

Preparations of acidic ionic liquids and their silica gel supported counterparts

Acidic ionic liquids and their silica gel supported counterparts, as shown in Scheme 1, were prepared using previously reported methods [7]. Sulfuric acid modified silica gel was synthesized according to the method described in Ref. [8]. Converting the sulfuric acid group on the silica gel to sulfonylchloride was performed as previously reported in Ref. [7]. Element analyses of the solid catalysts revealed that the acid amounts of ILIS–SO3H, ILIS–SO2Cl, SiO2–SO3H and SiO2–SO2Cl were 0.29, 0.17,

Characterizations of the acidities of ionic liquids using UV–visible spectroscopy and the relationship between acidity and activity

Though the dehydration reaction of fructose to HMF in the presence of acidic ionic liquids has been previously reported, few studies have been completed to illustrate the relationship between the acidities of the ionic liquids and their activities in this reaction. It has been suggested that the reaction performance of the dehydration reaction of fructose to HMF is closely associated with both the acidity strength and the acidity type of the catalyst [9]. Therefore, characterizations of the

Conclusions

Preparation of HMF through the dehydration reaction of fructose is one of the most important approaches to utilize biomass as promising surrogates for petroleum-based chemicals. It was demonstrated herein that this reaction could be smoothly carried out in the presence of both Brønsted and Lewis acidic ionic liquids and their silica gel immobilized counterparts using microwave irradiation as the heating source. The feasibility of characterizing the Lewis acidity of the ionic liquid using

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