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Research Article pubs.acs.org/journal/ascecg

Room-Temperature Ionic Liquid System Converting Fructose into 5‑Hydroxymethylfurfural in High Efficiency Jing Zhang,† Xinxin Yu,† Feixue Zou,† Yaohua Zhong,‡ Na Du,† and Xirong Huang*,† †

Key Lab for Colloid and Interface Chemistry of the Education Ministry of China, Shandong University, Jinan 250100, China State Key Laboratory of Microbial Technology of China, Shandong University, Jinan 250100, China

‡

ABSTRACT: This report describes a dehydration of fructose into 5-hydroxymethylfurfural (HMF) promoted by ionic liquids [Bmim]Cl and [HNMP][CH3SO3] in ethanol solvent. Two intermediates captured in time-dependent HPLC determinations are identified and structurally characterized by in situ 1H NMR and online ESI(+)-MS/MS. Studies on the influence of the ionic liquids (ILs) on the formation and transformation of the intermediates indicate that [HNMP][CH3SO3] promotes the formation of the intermediates, while [Bmim]Cl promotes their transformation. The contribution of the component ions of the ILs to the dehydration originates from their activation toward the leaving of OH on fructose or the intermediates via the formation of multiple hydrogen bonds. This kind of weak interaction appears only at low temperature. On the basis of the present study and the related literature, we propose a concerted mechanism for the binary IL-promoted conversion of fructose into HMF at room temperature. KEYWORDS: Fructose, 5-Hydroxymethylfurfural, Ionic liquids, Hydrogen bond, Concerted mechanism

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INTRODUCTION 5-Hydroxymethylfurfural (HMF) is a new platform chemical.1−6 Much effort has been devoted to the conversion of fructose into HMF.7−13 Recently, the use of ionic liquids (ILs) as media for fructose dehydration has gained increasing attention due to the public concern for environmental degradation.14−22 The halide-based ILs such as 1-butyl-3methylimidazolium chloride ([Bmim]Cl) are demonstrated to be good solvents for the conversion. Moreover, some functionalized ILs (e.g., N-methyl-2-pyrrolidonium methyl sulfonate ([HNMP][CH3SO3])), albeit few, are found to be catalytically active toward the conversion.23−29 However, the IL-involved conversions were mostly carried out at high temperature (>80 °C). High temperature favors the dehydration of sugars, but it also gives rise to byproducts (e.g., levulinic acid and humin), thereby reducing HMF yield and selectivity. Furthermore, the high energy consumption would limit its practical application. To avoid the defects under high temperature and to reduce the energy consumption, fructose dehydration should be carried out at room temperature. However, the reported ILs used as solvents (e.g., [Bmim]Cl) or catalysts (e.g., [HNMP][CH3SO3]) for the conversion are solid at room temperature. To lower the melting points of the ILs used for IL-based green conversion of fructose into HMF, a deep eutectic solvent (DES) has been tried.30,31 König et al. found that fructose could act as a hydrogen-bond donor and formulate a DES with choline chloride (ChCl) at a certain ratio, lowering the melting point of ChCl from 320 to 79 °C.32 Han et al. reported that © XXXX American Chemical Society

oxalic acid, citric acid, and p-toluene sulfonic acid (as hydrogenbond donors as well as acid catalysts for fructose dehydration) are also able to form DESs with ChCl.33,34 In these DES systems, fructose can be efficiently converted into HMF, but the required reaction temperature is still higher than room temperature (>50 °C) partly due to relatively high eutectic temperature. To realize the room-temperature conversion, some molecular solvents35−38 (e.g., CHCl3,35 DMSO,36 acetone,37 etc.) have to be used as the solvents of the ILs. Compared with the aprotic molecular solvents mentioned above, the protonic solvents of alcohol, especially ethanol, can be regarded as a green solvent. Moreover, ILs (e.g., [Bmim]Cl and [HNMP][CH3SO3]) usually have a good solubility in ethanol, which is the foundation for green and efficient room-temperature conversion of fructose. There have been some reports on the hightemperature conversion of fructose in the medium of ethanol into HMF39−41 or biofuel (etherified products of HMF with alcohol under high temperature).28,42−46 A study on the ILpromoted conversion of fructose into HMF in the medium of alcohol at room temperature has not been reported. Here, we describe an IL/ethanol system for fructose dehydration of into HMF at room temperature. The ILs used are [Bmim]Cl and [HNMP][CH3SO3]. It is found that the room-temperature conversion is promoted by both [HNMP]Received: September 3, 2015 Revised: November 7, 2015

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DOI: 10.1021/acssuschemeng.5b01015 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

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ACS Sustainable Chemistry & Engineering [CH3SO3] and [Bmim]Cl, and a high HMF yield could be obtained at room temperature. A concerted mechanism for the binary IL-promoted conversion of fructose into HMF in ethanol at room temperature is proposed based on the present study.

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EXPERIMENTAL SECTION

Materials. 5-Hydroxymethylfurfural (HMF) was obtained commercially from J&K Chemical Ltd. 1-Ethyl-3-methylimidazolium chloride ([Emim]Cl), 1-hexyl-3-methylimidazolium chloride ([Hmim]Cl), 1-butyl-3-methylimidazolium bromide ([Bmim]Br), [Bmim]Cl, and [HNMP][CH3SO3] were purchased from Shanghai Chengjie Chemicals Co. Ltd., China. Fructose, methylsulfonic acid (CH3SO3H), dimethyl sulfoxide (DMSO), ethanol, and acetonitrile were purchased from Sinopharm Chemical Reagent Co. Ltd., China. All reagents excluding acetonitrile (HPLC grade) were of analytical grade and used without further purification. Triply distilled water was used throughout the experiments. Typical Procedure for the Conversion of Fructose into HMF. All the fructose dehydration reactions were carried out in a 5 mL airtight glass flask. First, 5.72 mmol (1.0 g) [Bmim]Cl and 0.572 mmol [HNMP][CH3SO3] were dissolved in 10 mmol ethanol, and then 0.278 mmol (50 mg) fructose was added. The resulting system was stirred at 600 rpm for a certain period of time at 25 °C. At the end of the reaction, the resulting mixture was diluted with ultrapure water and then analyzed by HPLC. HPLC Analysis. HMF was quantified by external standard at 25 °C using an HPLC apparatus equipped with a Shim-pak VP-ODS C18 column (250 mm × 4.6 mm), a Shimadzu LC-20AT pump, and a Shimadzu SPD-20A detector. The mobile phase was a mixture of acetonitrile and water (10/90 v/v). The flowing rate was set at 1.0 mL min−1, and the detection wavelength was 283.0 nm. Fructose was quantified by external standard at 25 °C using an HPLC apparatus equipped with a Hypersil NH2 column (250 mm × 4.6 mm), a Shimadzu LC-20AT pump, and a Shimadzu RID-10A detector. The mobile phase was a mixture of acetonitrile and water (75/25 v/v). The flowing rate was set at 0.9 mL min−1. The separation conditions for intermediates were same as for fructose. Mass Spectrometry of Intermediates. The identification and structural characterization of intermediates were performed on an Agilent 6510Q-TOF mass spectrometer equipped with an electrospray ionization (ESI) source. The typical operating conditions for MS scan in positive ESI mode were as follows: fragmentor voltage was set at 125 V, capillary at 3500 V, and N2 was used as the drying (350 °C, 9 L min−1) and nebulizing (40 psi) gas. The scan range was over 50−1000 m/z. For collision-induced dissociation experiments, ultrahigh pure argon gas was used as collision gas. The precursor ion of interest was selected using the quadrupole analyzer, and the product ions were analyzed using the TOF analyzer. In Situ NMR Analysis. 1H NMR spectra were recorded on a Bruker 300 spectrometer at 25 °C. A solution contained 0.278 mmol fructose, 2.86 mmol [Bmim]Cl, 0.572 mmol [HNMP][CH3SO3], and 10 mmol deuterated ethanol was prepared in a 5 mm (i.d.) NMR tube (deuterated ethanol was used as internal standard). The tube was then quickly transferred into the chamber of the spectrometer, followed by recording the 1H (rd = 2 s, NS = 32) NMR spectra at regular time intervals.

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Figure 1. (a) Fructose conversion and HMF yield at different [HNMP][CH3SO3] loading. Reaction conditions: 0.278 mmol fructose, 5.72 mmol [Bmim]Cl, and varied amount of [HNMP][CH3SO3] were dissolved in 10 mmol ethanol, and the resulting mixture was then stirred at 25 °C for 3 h. (b) Time dependent fructose conversion, HMF yield, and HMF selectivity. Reaction conditions: same as in panel (a) except that [HNMP][CH3SO3] was fixed at 0.572 mmol.

room temperature [HNMP][CH3SO3] is indeed able to efficiently promote the conversion of fructose into HMF. Figure 1a also shows that the HMF yield is always lower than the fructose conversion with the least difference of ca. 13%. To ascertain whether this difference is caused by side reactions, the etherification of HMF with ethanol in the absence of fructose but with [Bmim]Cl/[HNMP][CH3SO3] was monitored using HPLC technique. It was found that at room temperature HMF remains unchanged in 6 h. At high temperatures (>70 °C), however, appreciable 5-ethoxymethylfurfural (EMF) was detected.42−46 To explain the difference in Figure 1a, the time dependence of the fructose conversion, HMF yield, and HMF selectivity was studied at the optimum amount of [HNMP][CH3SO3]. As shown in Figure 1b, in the initial stage, the fructose conversion and the HMF yield increase very fast, but the HMF yield is much lower than the corresponding fructose conversion. In other words, the selectivity of HMF is low in the initial stage. With an increase in reaction time, however, the difference between fructose conversion and HMF yield reduces gradually and HMF selectivity increases steadily. The HMF selectivity is up to 90% after 6 h reaction, and 24 h later it reaches 95%. Additionally, no EMF was detected in the process. These results suggest that it is the formation of intermediates and their transformation, not the side reactions, that determine the selectivity of HMF. In the present system, the conversion of fructose into intermediates seems to be very fast, whereas the conversion of intermediates into HMF slow. Usually [Bmim]Cl is used as the solvent for sugar dissolution.20 It is also reported that [Bmim]Cl is able to promote the dehydration of fructose into HMF at high

RESULTS AND DISCUSSION

IL-Promoted Fructose Dehydration. The conversion of fructose into HMF in [Bmim]Cl/[HNMP][CH3SO3] ILs in ethanol was investigated at a room temperature of 25 °C. As shown in Figure 1a, the fructose conversion at a constant level of [Bmim]Cl increases with an increase in loading of [HNMP][CH3SO3] and then levels off (ca. 92%). The HMF yield has a similar profile to the fructose conversion with the highest HMF yield of 78.4%. These results indicate that at B


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ACS Sustainable Chemistry & Engineering temperature (100 °C).29 Table 1 shows that at room temperature [Bmim]Cl alone (without [HNMP][CH3SO3]) Table 1. Effect of Level of [Bmim]Cl on Conversion of fructose and Yield of HMFa entrya

[Bmim]Cl (mmol)

[HNMP][CH3SO3] (mmol)

fructose conversion (%)

HMF yield (%)

1 2 3 4 5 6 7

0.572 − 0.572 1.144 2.288 4.576 5.720

− 0.572 0.572 0.572 0.572 0.572 0.572

0 65.89 73.47 79.70 89.92 92.58 96.90

0 4.35 23.18 31.04 51.55 82.47 89.16

a

Reaction conditions: 0.278 mmol fructose, 0.572 mmol [HNMP][CH3SO3], and a certain level of [Bmim]Cl were all dissolved in 10 mmol ethanol, and the resulting mixture was then stirred at 25 °C for 6 h.

Figure 2. 1H NMR spectra of the fructose dehydration system at different times. Left: prior to magnification; right: after local magnification.

dehydration system at different times. Compared with the control system (without fructose), the fructose dehydration system has new peaks at 4.74, 6.79, and 9.83 ppm, which increase with the reaction time (Figure 2, these new peaks were assigned to HMF48,49). After magnification, two more peaks at 5.67 and 6.43 ppm can be observed, and moreover, both peaks increase first and then decrease with time (their timedependent changes are not synchronous), indicating the existence of two intermediates. On the basis of the reported conversion mechanism,50−52 we suggest that in the present strongly polar medium, the dehydration of fructose goes probably through the following basic route (Scheme 1): fructose 1 is first converted to

cannot effectively promote the conversion of fructose into HMF (almost no HMF was detected after 6 h reaction at 25 °C). Likewise, [HNMP][CH3SO3] alone cannot either (HMF yield is less than 5% after 6 h reaction at 25 °C), even though it is a good catalyst for fructose conversion at high temperature (e.g., 90 °C).25,28 In the presence of both [Bmim]Cl and [HNMP][CH3SO3], however, the HMF yield increases greatly, indicating that the two ILs have a concerted promoting effect on the room temperature conversion of fructose into HMF. This is an interesting phenomenon that has never been reported. For a given amount of [HNMP][CH3SO3], the HMF yield increases with an increase in loading of [Bmim]Cl. When the molar ratio of [Bmim]Cl to [HNMP][CH3SO3] rises to 10:1, a maximum HMF yield of 89.16% can be obtained after 6 h reaction at 25 °C. Under this condition, the loading of [Bmim]Cl is much higher than that of fructose, indicating low activity of [Bmim]Cl in the ethanol system. The possible reason is that the hydrogen-bond (H-bond) interaction between ethanol and [Bmim]Cl could weaken the promoting effect of [Bmim]Cl for fructose dehydration.47 When ethanol was replaced by equimolar DMSO, the HMF yield did enhance (increment is ca. 12% at 2.86 mmol [Bmim]Cl/0.572 mmol [HNMP][CH3SO3]). It is noteworthy that the HMF yield in the absence of [Bmim]Cl is very low, but the fructose conversion is as high as 65.89% after 6 h reaction. Combined with the result that fructose is not converted at all without [HNMP][CH3SO3] at 25 °C, we can conclude that the fructose dehydration reaction goes through several different stages, and probably [HNMP][CH3SO3] promotes the initial dehydration step, while [Bmim] Cl promotes the subsequent steps. Intermediates during Fructose Dehydration. By comparing the HPLC chromatograms of the fructose dehydration system sampled at different reaction times, we found two peaks of unknown species (their retention times were 5.10 and 5.50 min, respectively). The peak areas of the two species vary with the time with a bell shape, suggesting that they are the intermediates formed during the fructose dehydration. To confirm the existence of the intermediates, in situ 1H NMR was also used to detect the process of fructose dehydration. Figure 2 is the 1H NMR spectra of the fructose

Scheme 1. Basic Route of Dehydration of Fructose into HMF

intermediate 2, then to intermediate 3, and finally to HMF 4. The two intermediates captured in HPLC were probably 2 and 3, which is corroborated by the 1H NMR study. The 1H NMR signal at 6.43 ppm in Figure 2 could be assigned to the C-3 olefinic hydrogen of 3,48 and the signal at 5.67 ppm (which peaks earlier than that at 6.43 ppm) could be assigned to the C2 hydrogen of 2 (only in 2 does C-2 have a hydrogen). To confirm the structures of 2 (molecular weight is 162) and 3 (molecular weight is 144), electrospray ionization mass spectrometry was used to intercept and characterize the proposed intermediates.53 To simplify the analysis, a fructose conversion system without [Bmim]Cl was chosen and monitored online. Figure 3 is the ESI(+)-MS for the conversion system recorded after 30 min reaction. The main peaks can be C


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z 69 (occurred in Figure 4a and 4b), support the structures of 2 and 3. Effects of ILs on Intermediates. As mentioned earlier, [HNMP][CH3SO3] is indispensable to the fructose dehydration. Without [HNMP][CH3SO3], fructose is unable to dehydrate in the present system, and therefore, no intermediates and products form. With [HNMP][CH3SO3] but without [Bmim]Cl, however, 2 forms very fast, but its subsequent transformation is very slow (Figure 5a). In the presence of both [HNMP][CH3SO3] and [Bmim]Cl, the transformation of 2 enhances. Intermediate 3 has similar behaviors to 2, but the formation of 3 is relatively slow, and its transformation is fast (Figure 5b). Combined with the results that the fructose conversion is more than 50% after 60 min reaction, while the HMF yield is very low (Figure 5c and d), we conclude that fructose can rapidly lose a molecule of water to form 2 in the presence of [HNMP][CH3SO3], but the subsequent two dehydration steps are very slow. In the presence of both [Bmim]Cl and [HNMP][CH3SO3] (in a molar ratio of 1:1), the formation rates of 2 and 3 change little, but their transformation rates increase significantly, especially for 2. Although the conversion rate of fructose increases little under this condition, the yield of HMF increases markedly. Thus, we can draw a conclusion that [HNMP][CH3SO3] mainly promotes the formation of the intermediates, while [Bmim]Cl promotes their transformation. Contributions from the Cation and Anion of ILs. To better understand the activation mechanism of [HNMP][CH3SO3] and [Bmim]Cl, we investigated the effects of the component ions of the ILs on the dehydration of fructose. Table 2 shows the individual ion contribution to HMF formation. The comparison of entry 1 with entry 5 indicates that [HNMP]+ is a key ion for fructose dehydration. Without [HNMP]+, no HMF forms. Entries 2 and 5 show comparable HMF yield, indicating that [CH3SO3]− has little effect. The difference in HMF yield between entries 3 and 5 is ca. 4.7%, demonstrating that [Bmim]+ is able to enhance the reaction. The significant difference in HMF yield between entries 4 and 5 demonstrates that Cl− is also a key ion. It follows that [HNMP]+, [Bmim]+, and Cl− are the major ions responsible for the high HMF yield. Their relative contribution is as follows: [HNMP]+ > Cl− > [Bmim]+. Activation Mechanism of [HNMP]+. It is known that inorganic acids are capable of accelerating the dehydration of fructose into HMF. To understand the role of [HNMP]+ in the conversion, the activation capacities of H+ and [HNMP]+ (with the same anion [CH3SO3]−) toward the conversion were measured and compared. Under the same conditions (5.72 mmol [Bmim]Cl and 0.572 mmol [HNMP][CH3SO3] or CH3SO3H; other conditions the same as in Table 2), the HMF yield under [HNMP][CH3SO3] (80.27%) is much higher than that under CH3SO3H (60.90%). In other words, the activation capacity of [HNMP]+ is much higher than that of H+. It suggests that, during the fructose dehydration, not only the Nbonded hydrogen, but also the adjacent keto oxygen on [HNMP]+ is involved in the activation of the C-2 OH of fructose through the formation of multiple intermolecular Hbonds (forming relatively stable six-membered ring, Scheme 2a). Activation Mechanisms of [Bmim]Cl. It is known that secondary OH is more difficult to dehydrate than tertiary OH. For fructose, the dehydration of the C-3 or C-4 OH on 2 or 3 is more difficult than that of the C-2 OH on 1. We conjecture that

Figure 3. ESI(+)-MS spectrum of the fructose conversion system recorded after 30 min reaction at 25 °C. The reaction system was composed of 0.278 mmol fructose, 0.572 mmol [HNMP][CH3SO3], and 10 mmol ethanol.

assigned to [4+H]+ (m/z 127), [3+H]+ (m/z 145), [2+H]+ (m/z 163), [4+CH3CH2OH+H]+ (m/z 173), and [2+NH4]+ (m/z 180). The control experiment (without any ILs) indicates that, under the present mild conditions, ESI-MS itself contributes little to the formation of the intermediates via splitting water from pure fructose. For further confirmation, [2+H]+ and [3+H]+ as the precursor ions were selected for ESI(+)-MS/MS analysis (Figure 4). The product ions [3+H]+ (m/z 145) and [4+H]+ (m/z 127) generated from the precursor ion [2+H]+ in Figure 4a, as well as the characteristic fragment ions at m/z 55 and m/

Figure 4. ESI(+)-MS/MS for CID of the intermediate species (a) (upper, [2+H]+, m/z 163) and (b) (lower, [3+H]+, m/z 145) intercepted from the reaction solution. D


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Figure 5. Variations of the intermediates 2 (a) and 3 (b) peak areas, fructose conversion (c), and HMF yield (d) with time at 25 °C. Reaction conditions: 0.278 mmol fructose, 17 mmol ethanol, 0.572 mmol [HNMP][CH3SO3], and 0.572 mmol [Bmim]Cl.

Table 2. Contributions of Component Ions of ILs to Fructose Dehydrationa entrya

ion probed

ILs composition

HMF yield (%)

1 2 3 4 5

[HNMP]+ [CH3SO3]− [Bmim]+ Cl− control system

[Bmim]Cl + [Bmim][CH3SO3] [Bmim]Cl + [HNMP]Cl [HNMP]Cl + [HNMP][CH3SO3] [Bmim][CH3SO3] + [HNMP][CH3SO3] [Bmim]Cl + [HNMP][CH3SO3]

0 22.56 16.44 2.93 21.16

a

Reaction conditions: 0.278 mmol fructose and binary ILs (both ILs were 0.572 mmol) were dissolved in 10 mmol ethanol, and the resulting mixture was then stirred at 25 °C for 4 h.

Scheme 2. Proposed Activation Mechanism of [HNMP]+ (a) and [Bmim]Cl (b)

Table 3. Fructose Dehydration under Different Halide-Based ILsa IL

fructose conversion (%)

HMF yield (%)

[Bmim]Br [Emim]Cl [Bmim]Cl [Hmim]Cl

87.01 94.32 88.31 73.54

62.97 80.35 68.75 29.86

a

Reaction conditions: 0.278 mmol fructose, 0.572 mmol [HNMP][CH3SO3], and 5.72 mmol halogenated ILs were dissolved in 10 mmol ethanol, and the resulting mixture was then stirred at 25 °C for 2 h.

higher electronegativity of Cl− results in a stronger H-bond interaction with the leaving of OH. Table 3 also shows that for chloride-based ILs, both the conversion of fructose and the yield of HMF decrease with an increase of the alkyl chain length of imidazolium cation. The highest HMF yield results from [Emim]Cl (80.35% after 2 h reaction). This finding is in accord with the reported result that the ability of the imidazolium cation to form a H-bond with a given acceptor reduces with an increase in the alkyl chain length.54 It follows that the concerted promoting effect by [Bmim]Cl is closely correlated to its involvement in the formation of H-bonds with the intermediates (Scheme 2b). Obviously, only at low temperature does this weak interaction appear. To confirm the above inference, online ESI(+)-MS was used to capture the transient species formed during the fructose conversion in [Bmim]Cl/[HNMP][CH3SO3]/CH3CH2OH (Figure 6). Probably due to the fast dehydration of tertiary

the promoted transformation of the intermediates by [Bmim] Cl is presumably due to the formation of H-bonds between the component ions and OH involved in the transformation, which accelerates the proton transfer of [HNMP]+ to the leaving of OH. In fact, the good solubility of sugar in the halide-based imidazolium ILs is attributed to the destructive effects of their cations and anions on the intermolecular H-bonds in sugar.54 To verify this conjecture, we studied the fructose dehydration under different halide-based imidazolium ILs. Table 3 shows that the efficiency of fructose dehydration under [Bmim]Cl is slightly better than that under [Bmim]Br. This room temperatire result is opposite to the corresponding high temperature result, which is reported by Li et al.29 A possible explanation is that the H-bond interaction at room temperature is much more prominent than that at high temperature, and the E


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interaction). These results support the proposed activation mechanism of [Bmim]Cl. Overall Fructose Dehydration Mechanism. On the basis of the present study and the related literature, we propose a concerted mechanism for the IL-promoted dehydration of fructose into HMF in ethanol solvent at room temperature (Scheme 3). Conversion of Other Sugars. The conversions of glucose and sucrose under the same conditions were also investigated separately. Table 4 indicates that the HMF yields from glucose Table 4. Comparison of HMF Yield from Different Sugars under the Same Conditionsa HMF yield under chlorinated IL (%)

Figure 6. ESI(+)-MS spectrum of the conversion of fructose in the system of [Bmim]Cl/[HNMP][CH3SO3]/CH3CH2OH. The molar ratio of [Bmim]Cl to [HNMP][CH3SO3] was 10/1. After 20 min reaction at 25 °C, an aliquot of sample was taken from the reaction system and diluted with ethanol for analysis.

sugar

[Emim]Cl

[Bmim]Cl

glucose sucrose fructose

0.93 41.90 80.35b

0.57 40.34 89.16

a

+

Reaction conditions: 0.278 mmol sugar, 0.572 mmol [HNMP][CH3SO3], and 5.72 mmol chlorinated IL were dissolved in 10 mmol ethanol, and the resulting mixture was then stirred at 25 °C for 6 h. b2 h conversion.

+

OH and therefore short-lived [1a] , the peak of [1a] or its associate with CH3CH2OH was not observed. However, the associates of 2a and 3a with CH3CH2OH were observed. The peaks at m/z 464 and m/z 482 could be assigned to [3a +CH 3 CH 2 OH] + and [2a+CH 3 CH 2 OH] + , respectively (CH3CH2OH may be brought in by Cl− via H-bond

and sucrose are much lower than that from fructose. After 6 h conversion in [Bmim]Cl/[HNMP][CH3SO3]/CH3CH2OH,

Scheme 3. Proposed Concerted Mechanism for Dehydration of Fructose into HMF by Both [HNMP][CH3SO3] and [Bmim]Cl at Room Temperature

F


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(11) Yi, X.; Delidovich, I.; Sun, Z.; Wang, S.; Wang, X.; Palkovits, R. A heteropoly acid ionic crystal containing Cr as an active catalyst for dehydration of monosaccharides to produce 5-HMF in water. Catal. Sci. Technol. 2015, 5, 2496. (12) Pedersen, A. T.; Ringborg, R.; Grotkjær, T.; Pedersen, S.; Woodley, J. M. Synthesis of 5-hydroxymethylfurfural (HMF) by acid catalyzed dehydration of glucose-fructose mixtures. Chem. Eng. J. 2015, 273, 455. (13) Tucker, M. H.; Alamillo, R.; Crisci, A. J.; Gonzalez, G. M.; Scott, S. L.; Dumesic, J. A. Sustainable solvent systems for use in tandem carbohydrate dehydration hydrogenation. ACS Sustainable Chem. Eng. 2013, 1, 554. (14) Zhao, H.; Holladay, J. E.; Brown, H.; Zhang, Z. Metal chlorides in ionic liquid solvents convert sugars to 5-hydroxymethylfurfural. Science 2007, 316, 1597. (15) Yong, G.; Zhang, Y.; Ying, J. Y. Efficient catalytic system for the selective production of 5-hydroxymethylfurfural from glucose and fructose. Angew. Chem., Int. Ed. 2008, 47, 9345. (16) Hu, S.; Zhang, Z.; Zhou, Y.; Han, B.; Fan, H.; Li, W.; Song, J.; Xie, Y. Conversion of fructose to 5-hydroxymethylfurfural using ionic liquids prepared from renewable materials. Green Chem. 2008, 10, 1280. (17) Qi, X.; Watanabe, M.; Aida, T. M.; Smith, R. L., Jr. Efficient process for conversion of fructose to 5-hydroxymethylfurfural with ionic liquids. Green Chem. 2009, 11, 1327. (18) Stahlberg, T.; Fu, W.; Woodley, J. M.; Riisager, A. Synthesis of 5-(hydroxymethyl)furfural in ionic liquids: Paving the way to renewable chemicals. ChemSusChem 2011, 4, 451. (19) Zakrzewska, M. E.; Bogel-Lukasik, E.; Bogel-Lukasik, R. Ionic liquid-mediated formation of 5-hydroxymethylfurfural-A promising biomass-derived building block. Chem. Rev. 2011, 111, 397. (20) Zhang, S.; Sun, J.; Zhang, X.; Xin, J.; Miao, Q.; Wang, J. Ionic liquid-based green processes for energy production. Chem. Soc. Rev. 2014, 43, 7838. (21) Liu, D.; Chen, E. Y.-X. Integrated catalytic process for biomass conversion and upgrading to C12 furoin and alkane fuel. ACS Catal. 2014, 4, 1302. (22) Eminov, S.; Wilton-Ely, J. D. E. T.; Hallett, J. P. Highly selective and near-quantitative conversion of fructose to 5-hydroxymethylfurfural using mildly acidic ionic liquids. ACS Sustainable Chem. Eng. 2014, 2, 978. (23) Jadhav, A. H.; Kim, H.; Hwang, I. T. Efficient selective dehydration of fructose and sucrose into 5-hydroxymethylfurfural(HMF) using dicationic room temperature ionic liquids as a catalyst. Catal. Commun. 2012, 21, 96. (24) Moreau, C.; Finiels, A.; Vanoye, L. Dehydration of fructose and sucrose into 5-hydroxymethylfurfural in the presence of 1-H-3-methyl imidazolium chloride acting both as solvent and catalyst. J. Mol. Catal. A: Chem. 2006, 253, 165. (25) Tong, X.; Li, Y. Efficient and selective dehydration of fructose to 5-hdroxymethylfurfural catalyzed by Brønsted-acidic ionic liquids. ChemSusChem 2010, 3, 350. (26) Shi, J.; Liu, W.; Wang, N.; Yang, Y.; Wang, H. Production of 5hydroxymethylfurfural from mono- and disaccharides in the presence of ionic liquids. Catal. Lett. 2014, 144, 252. (27) Ma, Y.; Qing, S.; Wang, L.; Islam, N.; Guan, S.; Gao, Z.; Mamat, X.; Li, H.; Eli, W.; Wang, T. Production of 5-hydroxymethylfurfural from fructose by a thermo-regulated and recyclable Brønsted acidic ionic liquid catalyst. RSC Adv. 2015, 5, 47377. (28) Alam, M. I.; De, S.; Dutta, S.; Saha, B. Solid-acid and ionic-liquid catalyzed one-pot transformation of biorenewable substrates into a platform chemical and a promising biofuel. RSC Adv. 2012, 2, 6890. (29) Li, Y.; Wang, J.; He, L.; Yang, Z.; Liu, A.; Yu, B.; Luan, C. Experimental and theoretical studies on imidazolium ionic liquidpromoted conversion of fructose to 5-hydroxymethylfurfural. Green Chem. 2012, 14, 2752. (30) Abbott, A. P.; Boothby, D.; Davies, G. L.; Rasheed, R. K.; Capper, G. Deep eutectic solvents formed between choline chloride

the HMF yield from sucrose is ca. 40%, while the yield from glucose is less than 1%. These results indicate that the isomerization of glucose is a key step for its efficient conversion into HMF, which is catalyzed by a base or a Lewis acid.6,14 Due to the presence of trace water, sucrose (the dimmer of glucose and fructose) can be hydrolyzed into fructose, which can then be efficiently converted into HMF under the catalysis of an acid.26

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CONCLUSIONS The conversion of fructose into HMF promoted by [Bmim]Cl and [HNMP][CH3SO3] in ethanol solvent was first investigated at room temperature. Not only [HNMP][CH3SO3] but also [Bmim]Cl was found to promote the conversion. Mechanistic studies indicate that [HNMP][CH3SO3] promotes the formation of the intermediates, while [Bmim]Cl promotes their transformation. The formation of multiple H-bonds (only work at low temperature) is responsible for their activation toward the leaving of OH on fructose or the intermediates.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful for the financial support from the Fundamental Research Funds of Shandong University (2015CJ005), Provincial Key R & D Project of Shandong (2015GSF121035), and National Natural Science Foundation of China (20973103 and 21173133).

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REFERENCES

(1) Mascal, M.; Nikitin, E. B. Direct, high-yield conversion of cellulose into biofuel. Angew. Chem., Int. Ed. 2008, 47, 7924. (2) Binder, J. B.; Raines, R. T. Simple chemical transformation of lignocellulosic biomass into furans for fuels and chemicals. J. Am. Chem. Soc. 2009, 131, 1979. (3) Rosatella, A. A.; Simeonov, S. P.; Frade, R. F. M.; Afonso, C. A. M. 5-Hydroxymethylfurfural (HMF) as a building block platform: Biological properties, synthesis and synthetic applications. Green Chem. 2011, 13, 754. (4) Gallezot, P. Conversion of biomass to selected chemical products. Chem. Soc. Rev. 2012, 41, 1538. (5) van Putten, R.-J.; van der Waal, J. C.; de Jong, E.; Rasrendra, C. B.; Heeres, H. J.; de Vries, J. G. Hydroxymethylfurfural, a versatile platform chemical made from renewable resources. Chem. Rev. 2013, 113, 1499. (6) Wang, T.; Nolte, M. W.; Shanks, B. H. Catalytic dehydration of C6 carbohydrates for the production of hydroxymethylfurfural (HMF) as a versatile platform chemical. Green Chem. 2014, 16, 548. (7) Roman-Leshkov, Y.; Chheda, J. N.; Dumesic, J. A. Phase modifiers promote efficient production of hydroxymethylfurfural from fructose. Science 2006, 312, 1933. (8) Xie, H.; Zhao, Z.; Wang, Q. Catalytic conversion of inulin and fructose into 5-hydroxymethylfurfural by lignosulfonic acid in ionic liquids. ChemSusChem 2012, 5, 901. (9) Liu, F.; Barrault, J.; De Oliveira Vigier, K.; Jérôme, F. Dehydration of highly concentrated solutions of fructose to 5hydroxymethylfurfural in a cheap and sustainable choline chloride/ carbon dioxide system. ChemSusChem 2012, 5, 1223. (10) Richter, F. H.; Pupovac, K.; Palkovits, R.; Schüth, F. Set of acidic resin catalysts to correlate structure and reactivity in fructose conversion to 5-hydroxymethylfurfural. ACS Catal. 2013, 3, 123. G


Research Article

ACS Sustainable Chemistry & Engineering and carboxylic acids: versatile alternatives to ionic liquids. J. Am. Chem. Soc. 2004, 126, 9142. (31) Smith, E. L.; Abbott, A. P.; Ryder, K. S. Deep eutectic solvents (DESs) and their applications. Chem. Rev. 2014, 114, 11060. (32) Ilgen, F.; Ott, D.; Kralisch, D.; Reil, C.; Palmberger, A.; König, B. Conversion of carbohydrates into 5-hyfroxymethylfurfural in highly concentrated low melting mixtures. Green Chem. 2009, 11, 1948. (33) Hu, S.; Zhang, Z.; Zhou, Y.; Song, J.; Fan, H.; Han, B. Direct conversion of inulin to 5-hydroxymethylfurfural in biorenewable ionic liquids. Green Chem. 2009, 11, 873. (34) Assanosi, A. A.; Farah, M. M.; Wood, J.; Al-Duri, B. A facile acidic choline chloride-p-TSA DES-catalysed dehydration of fructose to 5-hydroxymethylfurfural. RSC Adv. 2014, 4, 39359. (35) Chan, J. Y. G.; Zhang, Y. Selective conversion of fructose to 5hydroxymethylfurfural catalyzed by tungsten salts at low temperatures. ChemSusChem 2009, 2, 731. (36) Zhang, Z.; Liu, B.; Zhao, Z. Conversion of fructose into HMF catalyzed by GeCl4 in DMSO and [Bmim]Cl system at room temperature. Carbohydr. Polym. 2012, 88, 891. (37) Qi, X.; Watanabe, M.; Aida, T. M.; Smith, R. L. Efficient catalytic conversion of fructose into 5-hydroxymethylfurfural in ionic liquids at room temperature. ChemSusChem 2009, 2, 944. (38) Lai, L.; Zhang, Y. The effect of imidazolium ionic liquid on the dehydration of fructose to 5-hydroxymethylfurfural, and a room temperature catalytic system. ChemSusChem 2010, 3, 1257. (39) Lai, L.; Zhang, Y. The production of 5-hydroxymethylfurfural from fructose in isopropyl alcohol: A green and efficient system. ChemSusChem 2011, 4, 1745. (40) Liu, J.; Tang, Y.; Wu, K.; Bi, C.; Cui, Q. Conversion of fructose into 5-hydroxymethylfurfural (HMF) and its derivatives promoted by inorganic salt in alcohol. Carbohydr. Res. 2012, 350, 20. (41) Wang, H.; Kong, Q.; Wang, Y.; Deng, T.; Chen, C.; Hou, X.; Zhu, Y. Graphene oxide catalyzed dehydration of fructose into 5hydroxymethylfurfural with isopropanol as cosolvent. ChemCatChem 2014, 6, 728. (42) Kraus, G. A.; Guney, T. A direct synthesis of 5alkoxymethylfurfural ethers from fructose via sulfonic acid-functionalized ionic liquids. Green Chem. 2012, 14, 1593. (43) Balakrishnan, M.; Sacia, E. R.; Bell, A. T. Etherification and reductive etherification of 5-(hydroxymethyl)furfural: 5(alkoxymethyl)furfurals and 2,5-bis(alkoxymethyl)furans as potential bio-diesel candidates. Green Chem. 2012, 14, 1626. (44) Wang, H.; Deng, T.; Wang, Y.; Qi, Y.; Hou, X.; Zhu, Y. Efficient catalytic system for the conversion of fructose into 5-ethoxymethylfurfural. Bioresour. Technol. 2013, 136, 394. (45) Yuan, Z.; Zhang, Z.; Zheng, J.; Lin, J. Efficient synthesis of promising liquid fuels 5-ethoxymethylfurfural from carbohydrates. Fuel 2015, 150, 236. (46) Bohre, A.; Dutta, S.; Saha, B.; Abu-Omar, M. M. Upgrading furfurals to drop-in biofuels: An overview. ACS Sustainable Chem. Eng. 2015, 3, 1263. (47) Hu, X.; Westerhof, R. J. M.; Dong, D.; Wu, L. P.; Li, C. Acidcatalyzed conversion of xylose in 20 solvents: Insight into interactions of the solvents with xylose, furfural, and the acid catalyst. ACS Sustainable Chem. Eng. 2014, 2, 2562. (48) Amarasekara, A. S.; Williams, L. D.; Ebede, C. C. Mechanism of the dehydration of D-fructose to 5-hydroxymethylfurfural in dimethyl sulfoxide at 150 degrees C: an NMR study. Carbohydr. Res. 2008, 343, 3021. (49) Zhang, J.; Weitz, E. An in situ NMR study of the mechanism for the catalytic conversion of fructose to 5-hydroxymethylfurfural and then to levulinic acid using 13C labeled D-fructose. ACS Catal. 2012, 2, 1211. (50) Antal, M. J.; Mok, W. S. L.; Richards, G. N. Mechanism of formation of 5-(hydroxymethyl)-2-furaldehyde from D-fructose and sucrose. Carbohydr. Res. 1990, 199, 91. (51) Nikbin, N.; Caratzoulas, S.; Vlachos, D. G. A first principlesbased microkinetic model for the conversion of fructose to 5hydroxymethylfurfural. ChemCatChem 2012, 4, 504.

(52) Akien, G. R.; Qi, L.; Horváth, I. T. Molecular mapping of the acid catalysed dehydration of fructose. Chem. Commun. 2012, 48, 5850. (53) Santos, L. S. Online mechanistic investigations of catalyzed reactions by electrospray ionization mass spectrometry: A tool to intercept transient species in solution. Eur. J. Org. Chem. 2008, 2008, 235. (54) Swatloski, R. P.; Spear, S. K.; Holbrey, J. D.; Rogers, R. D. Dissolution of cellose with ionic liquids. J. Am. Chem. Soc. 2002, 124, 4974.

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