- Email: [email protected]
Application of glucose derived magnetic solid acid for etherification of 5-HMF to 5-EMF, dehydration of sorbitol to isosorbide, and esterification of fatty acids
Tetrahedron Letters 57 (2016) 4398–4400
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Application of glucose derived magnetic solid acid for etherification of 5-HMF to 5-EMF, dehydration of sorbitol to isosorbide, and esterification of fatty acids Raju S. Thombal, Vrushali H. Jadhav ⇑ Division of Organic Chemistry, National Chemical Laboratory (CSIR-NCL), Pune 411008, India
a r t i c l e
i n f o
Article history: Received 14 June 2016 Revised 12 August 2016 Accepted 19 August 2016 Available online 21 August 2016 Keywords: Dehydration Etherification Esterification Magnetic
a b s t r a c t In this study, the catalytic activity of Glu-Fe3O4-SO3H was evaluated for three acid catalyzed reactions: etherification of 5-hydroxymethylfurfural (5-HMF) to 5-ethoxymethylfurfural (5-EMF) in ethanol, dehydration of sorbitol to isosorbide, and esterification of fatty acids with good yields and selectivity. Moreover, the catalyst can be easily separated from the reaction with an external magnetic force and reused at least five times without a significant decrease in catalytic activity. Ó 2016 Elsevier Ltd. All rights reserved.
The recent developments in the efficiency of the conversion of biomass into chemical materials have been of growing interest in sustainable chemistry. Synthesis of renewable fuels and value added chemicals from biomass generally require acidic materials. Homogeneous acid catalysts, e.g., mineral acids such as H2SO4, HCl have been used to catalyze such reactions.1 Homogeneous catalysts have several disadvantages, i.e., they are corrosive, expensive, forms large amount of waste by-products, and difficult to separate from the reaction medium. Hence heterogeneous catalysts have gained a lot of importance these days as they are greener and recyclable. Further compared to conventional heterogeneous solid acid catalyst, magnetic solid acids can be easily separated in the presence of external magnetic field particularly in viscous or solid reaction mixtures.2 5-Ethoxymethylfurfural (EMF),3–6 has gained increasing importance as a promising biofuel, since physical and chemical properties of this ether (liquid form at room temperature, high cetane number, good oxidation stability) make it a very interesting biofuel. Also, the energy density of EMF is 29% greater than that of ethanol and very close to that of diesel. Previously 5-EMF was synthesized from 5-CMF which in turn was obtained from 5-HMF.5 While this process gives high yields of EMF, there are concerns about HCl recyclability and the introduction of unreacted halides
⇑ Corresponding author. E-mail address: [email protected] (V.H. Jadhav). http://dx.doi.org/10.1016/j.tetlet.2016.08.061 0040-4039/Ó 2016 Elsevier Ltd. All rights reserved.
into automobile fuel systems, which can cause premature wear. Hence, production of EMF directly from HMF by etherification with ethanol has drawn increasing attention recently. Isosorbide,7,8 a material useful for polymer synthesis such as polycarbonates or polyesters, is important for the preparation of chemical feedstocks from biomass. Isosorbide is used for treating glaucoma, brain hypertension, and Ménière’s disease while isosorbide nitrates are medicines for angina pectoris. Though numbers of methodologies are reported for synthesis of isosorbide from sorbitol,9–13 still there is a need to develop an green and efficient procedure. Biodiesel is an environmentally friendly fuel since it is biodegradable, sustainable, and non-toxic.14 Biodiesel is a mixture of long chain fatty acid methyl esters (FAME) produced from free fatty acids, vegetable oil, animal oil, or waste oil via esterification, and/or trans-esterification with alcohols using acid or base.15 Base catalysts are generally not favoured as they react with fatty acids to form soaps and decrease the yield of biodiesel products. Highly reactive homogeneous Brønsted acid catalysts are efficient for this process, but they suffer from serious contamination and corrosion problems that require the implementation of good separation and purification steps. Hence there is a need to develop ideal heterogeneous catalysts that are cheap, not easily leachable, capable to efficiently catalyze the reaction with high yields and selectivity, easily separable, and reusable.16–18 Herein, we studied our recently synthesized Glu-Fe3O4-SO3H19 catalyst and showed its application for etherification of 5-HMF to 5-EMF, dehydration of sorbitol to isosorbide, and esterification of fatty acids.
4399
R. S. Thombal, V. H. Jadhav / Tetrahedron Letters 57 (2016) 4398–4400
tion did not show increase in yield of 5-EMF. We were also interested to study the conversion of components of biomass such as fructose, glucose, and inulin to 5-EMF. The catalyst Glu-Fe3O4SO3H when used with fructose in ethanol at 80 °C, underwent dehydration and etherification giving 55% yield of 5-EMF along with 10% yield of 5-HMF, whereas 50 wt % of catalyst gave about 81% yield of 5-EMF along with 7% yield of 5-HMF. When glucose was reacted with 50 wt % of catalyst in DMSO/ethanol (2:8) at 140 °C for longer times, 27% of 5-EMF was formed along with 8% of HMF. Inulin under similar reaction conditions as that of glucose gave 85% of 5-EMF along with 10% of 5-HMF after 24 h. 5-HMF, fructose, and inulin gave excellent yields of 5-EMF while, glucose also gave a good yield of 5-EMF. We then turned our attention to use Glu-Fe3O4-SO3H catalyst for sorbitol dehydration to isosorbide (Table 2). Initially, we tried the sorbitol dehydration in water using 10 wt % of catalyst at 120 °C. The starting remained unconsumed even after 12 h. Also when 30 wt % of catalyst was used at 140 °C, no formation of isosorbide was seen. The reaction was then carried out neat at 120 °C and 140 °C under various catalyst concentrations and it was observed that at 140 °C using 20 wt % of catalyst, 94% yield of isosorbide was obtained in 1 h. The isosorbide formation was confirmed by comparing the 1H and 13C NMR data with the reported data in the literature.9 The advantage of this method is that the reaction is carried out neat and no traces of any side products are formed in the reaction. Esterification of oleic acid with methanol was carried out using Glu-Fe3O4-SO3H catalyst under solvent free conditions (Table 3). When 5 wt % of the catalyst was used reaction was completed in 12 h giving 72% yield of methyl oleate. Hence the catalyst concentration was increased to 10 wt % and it was found that the reaction was completed in 4 h at rt giving 99% yield of methyl oleate. We used long chain oleic acid and long chain undecanol for esterification reaction which gave 98% yield of undecyloleate. Finally we also used the catalyst for esterification of acetic acid and long chain undecanol and the reaction gave excellent yield of undecylacetate. In all the above reactions, catalyst was easily separated by external magnetic force. Magnetically separated catalyst was dried at 100 °C for 12 h and reused. The catalyst showed excellent catalytic activity for at least five runs without any significant decrease in the yield of the products (Table 4). In conclusion, the glucose derived magnetic solid acid catalyst Glu-Fe3O4-SO3H has been conveniently studied in 5-EMF formation from 5-HMF and biomass components like fructose, glucose,
Table 1 Study on 5-EMF synthesis EtO
Glu-Fe3O4-SO 3H
5-HMF/Fructose/Glucose/Inulin
O
O
H
ethanol/DMSO:ethanol 5-EMF
a b c
Entry
Starting
Catalyst (wt %)
Temp (°C)
Time (h)
HMFa (%)
EMFa (%)
1 2 3 4 5 6 7 8
5-HMFb 5-HMFb 5-HMFb 5-HMFb Fructoseb Fructoseb Glucosec Inulinc
10 20 30 50 30 50 50 50
80 80 80 80 80 80 140 100
12 8 2 2 24 24 48 24
10 8 — — 10 7 8 10
28 70 92 92 55 81 27 85
Isolated yields. Solvent: ethanol. Solvent: ethanol/DMSO = 2:8.
Table 2 Study on sorbitol dehydration to isosorbide OH
OH OH
HO OH
Glu-Fe3O4-SO 3H
O
neat
OH
OH
O HO H Isosorbide
Sorbitol
a
H
Entry
Catalyst (wt %)
Solvent
Temp (°C)
Time (h)
Isosorbidea (%)
1 2 3 4 5 6
10 30 10 20 20 20
H2O H2O Neat Neat Neat Neat
120 140 120 120 120 140
12 12 5 2 5 1
— — 30 42 89 94
Isolated yields.
Initially we studied the catalytic activity of Glu-Fe3O4-SO3H for etherification of 5-HMF in ethanol (Table 1). The catalyst concentration was studied for the formation of 5-EMF. When 10 wt % and 20 wt % of catalyst was used at 80 °C, 5-HMF was not completely converted to 5-EMF even after prolonged reaction times. 30 wt % of catalyst at 80 °C gave complete conversion of 5-HMF to 5-EMF in 92% yield in 2 h. Further increase in catalyst concentra-
Table 3 Study on esterification of fatty acids O OH
+
Glu-Fe 3O 4-SO 3 H MeOH
neat
Oleic acid
O OMe O
Oleic acid + Undecanol
Glu-Fe 3O 4-SO 3 H
O
neat Undecanol + CH3 COOH
a
C11H 23
O
Glu-Fe 3 O4 -SO 3H O
neat
Entry
Acid
Alcohol
Catalyst (wt %)
Time (h)
Yielda (%)
1 2 3 4
Oleic acid Oleic acid Oleic acid Acetic acid
MeOH MeOH Undecanol Undecanol
5 10 10 10
12 4 5 2.5
72 99 98 98
Isolated yields.
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R. S. Thombal, V. H. Jadhav / Tetrahedron Letters 57 (2016) 4398–4400
Table 4 Reuse of Glu-Fe3O4-SO3H catalyst for 5-EMF, isosorbide, and methyl oleate formation Recycle a
EMF Isosorbideb Methyl Oleatec
1st
2nd
3rd
4th
5th
92 94 99
92 94 98
91 94 98
90 93 97
90 92 96
Reaction conditions: (a) HMF (0.1 g), ethanol (5 mL), Glu-Fe3O4-SO3H catalyst (30 wt %), 80 °C, 2 h, (b) Sorbitol (0.25 g), Glu-Fe3O4-SO3H catalyst (20 wt %), neat, 140 °C, 1 h, (c) Oleic acid (0.1 g), methanol (3 mL), Glu-Fe3O4-SO3H catalyst (10 wt %), neat, rt, 4 h.
and inulin. Dehydration of sorbitol to isosorbide and esterification of long chain fatty acids with alcohols gave excellent yields and selectivity. The catalyst was easily separated using external magnetic force and reused at least five times without any significant loss in yield of the products after every recycle. This catalytic system is environmentally friendly and can be used as an ideal method for etherification, dehydration, and esterification reactions in future. Acknowledgements V.H.J. thanks DST, New Delhi for the INSPIRE Faculty Award (IFA 12, CH-44) and Fast Track Grant (CS-041/2013). V.H.J. also thanks Director, NCL for providing all the infra-structural facilities. Supplementary data Supplementary data (detailed experimental procedure, characterization of the products and copies of spectra) associated with
this article can be found, in the online version, at http://dx.doi. org/10.1016/j.tetlet.2016.08.061. References and notes 1. Zhou, C. H.; Xia, X.; Lin, C. X.; Tong, D. S.; Beltramini, J. Chem. Soc. Rev. 2011, 40, 5588–5617. 2. Liu, W. J.; Tian, K.; Jiang, H.; Yu, H. Q. Sci. Rep. 2013, 3, 2419. 3. Wang, H.; Deng, T.; Wang, Y.; Cui, X.; Qi, Y.; Mu, X.; Hou, X.; Zhu, Y. Green Chem. 2013, 15, 2379–2383. 4. Wang, H.; Deng, T.; Wang, Y.; Qi, Y.; Hou, X.; Zhu, Y. Bioresour. Technol. 2013, 136, 394–400. 5. Mascal, M.; Nikitin, E. B. Angew. Chem., Int. Ed. 2008, 47, 7924–7926. 6. Balakrishnan, M.; Sacia, E. R.; Bell, A. T. Green Chem. 2012, 14, 1626–1634. 7. Fenouillot, F.; Rousseau, A.; Colomines, G.; Saint-Loupe, R.; Pascault, J.-P. Prog. Polym. Sci. 2010, 35, 578–622. 8. Rose, M.; Palkovits, R. ChemSusChem 2012, 5, 167–176. 9. Kamimura, A.; Murata, K.; Tanaka, Y.; Okagawa, T.; Matsumoto, H.; Kaiso, K.; Yoshimoto, M. ChemSusChem 2014, 7, 3257–3259. 10. Yamaguchi, A.; Hiyoshi, N.; Sato, O.; Shirai, M. Green Chem. 2011, 13, 873–881. 11. Li, J.; Spina, A.; Moulijn, J. A.; Makkee, M. Catal. Sci. Technol. 2013, 3, 1540–1546. 12. Dabbawala, A. A.; Mishra, D. K.; Huber, G. W.; Hwang, J. S. Appl. Catal. A: Gen. 2013, 456, 168–173. 13. Ahmed, I.; Khan, N. A.; Mishra, D. K.; Lee, J. S.; Hwang, J. S.; Jhung, S. H. Chem. Eng. Sci. 2013, 93, 91–95. 14. Su, F.; Guo, Y. Green Chem. 2014, 16, 2934–2957. 15. Poonjarernsilp, C.; Sano, N.; Sawangpanich, N.; Charinpanitkul, T.; Tamon, H. Green Chem. 2014, 16, 4936–4943. 16. Zhan, S.; Tao, X.; Cai, L.; Liua, X.; Liu, T. Green Chem. 2014, 16, 4649–4653. 17. Do Nascimentoa, L. A. S.; Titoa, L. M. Z.; Angélica, R. S.; Da Costaa, C. E. F.; Zamiana, J. R.; Da Rocha Filho, G. N. Appl. Catal. B: Environ. 2011, 101, 495–503. 18. Son, S. M.; Kimura, H.; Kusakabe, K. Bioresource Technol. 2011, 102, 2130–2132. 19. Thombal, R. S.; Jadhav, V. H. RSC Adv. 2016, 6, 30846–30851.
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Application of glucose derived magnetic solid acid for etherification of 5-HMF to 5-EMF, dehydration of sorbitol to isosorbide, and esterification of fatty acids Raju S. Thombal, Vrushali H. Jadhav ⇑ Division of Organic Chemistry, National Chemical Laboratory (CSIR-NCL), Pune 411008, India
a r t i c l e
i n f o
Article history: Received 14 June 2016 Revised 12 August 2016 Accepted 19 August 2016 Available online 21 August 2016 Keywords: Dehydration Etherification Esterification Magnetic
a b s t r a c t In this study, the catalytic activity of Glu-Fe3O4-SO3H was evaluated for three acid catalyzed reactions: etherification of 5-hydroxymethylfurfural (5-HMF) to 5-ethoxymethylfurfural (5-EMF) in ethanol, dehydration of sorbitol to isosorbide, and esterification of fatty acids with good yields and selectivity. Moreover, the catalyst can be easily separated from the reaction with an external magnetic force and reused at least five times without a significant decrease in catalytic activity. Ó 2016 Elsevier Ltd. All rights reserved.
The recent developments in the efficiency of the conversion of biomass into chemical materials have been of growing interest in sustainable chemistry. Synthesis of renewable fuels and value added chemicals from biomass generally require acidic materials. Homogeneous acid catalysts, e.g., mineral acids such as H2SO4, HCl have been used to catalyze such reactions.1 Homogeneous catalysts have several disadvantages, i.e., they are corrosive, expensive, forms large amount of waste by-products, and difficult to separate from the reaction medium. Hence heterogeneous catalysts have gained a lot of importance these days as they are greener and recyclable. Further compared to conventional heterogeneous solid acid catalyst, magnetic solid acids can be easily separated in the presence of external magnetic field particularly in viscous or solid reaction mixtures.2 5-Ethoxymethylfurfural (EMF),3–6 has gained increasing importance as a promising biofuel, since physical and chemical properties of this ether (liquid form at room temperature, high cetane number, good oxidation stability) make it a very interesting biofuel. Also, the energy density of EMF is 29% greater than that of ethanol and very close to that of diesel. Previously 5-EMF was synthesized from 5-CMF which in turn was obtained from 5-HMF.5 While this process gives high yields of EMF, there are concerns about HCl recyclability and the introduction of unreacted halides
⇑ Corresponding author. E-mail address: [email protected] (V.H. Jadhav). http://dx.doi.org/10.1016/j.tetlet.2016.08.061 0040-4039/Ó 2016 Elsevier Ltd. All rights reserved.
into automobile fuel systems, which can cause premature wear. Hence, production of EMF directly from HMF by etherification with ethanol has drawn increasing attention recently. Isosorbide,7,8 a material useful for polymer synthesis such as polycarbonates or polyesters, is important for the preparation of chemical feedstocks from biomass. Isosorbide is used for treating glaucoma, brain hypertension, and Ménière’s disease while isosorbide nitrates are medicines for angina pectoris. Though numbers of methodologies are reported for synthesis of isosorbide from sorbitol,9–13 still there is a need to develop an green and efficient procedure. Biodiesel is an environmentally friendly fuel since it is biodegradable, sustainable, and non-toxic.14 Biodiesel is a mixture of long chain fatty acid methyl esters (FAME) produced from free fatty acids, vegetable oil, animal oil, or waste oil via esterification, and/or trans-esterification with alcohols using acid or base.15 Base catalysts are generally not favoured as they react with fatty acids to form soaps and decrease the yield of biodiesel products. Highly reactive homogeneous Brønsted acid catalysts are efficient for this process, but they suffer from serious contamination and corrosion problems that require the implementation of good separation and purification steps. Hence there is a need to develop ideal heterogeneous catalysts that are cheap, not easily leachable, capable to efficiently catalyze the reaction with high yields and selectivity, easily separable, and reusable.16–18 Herein, we studied our recently synthesized Glu-Fe3O4-SO3H19 catalyst and showed its application for etherification of 5-HMF to 5-EMF, dehydration of sorbitol to isosorbide, and esterification of fatty acids.
4399
R. S. Thombal, V. H. Jadhav / Tetrahedron Letters 57 (2016) 4398–4400
tion did not show increase in yield of 5-EMF. We were also interested to study the conversion of components of biomass such as fructose, glucose, and inulin to 5-EMF. The catalyst Glu-Fe3O4SO3H when used with fructose in ethanol at 80 °C, underwent dehydration and etherification giving 55% yield of 5-EMF along with 10% yield of 5-HMF, whereas 50 wt % of catalyst gave about 81% yield of 5-EMF along with 7% yield of 5-HMF. When glucose was reacted with 50 wt % of catalyst in DMSO/ethanol (2:8) at 140 °C for longer times, 27% of 5-EMF was formed along with 8% of HMF. Inulin under similar reaction conditions as that of glucose gave 85% of 5-EMF along with 10% of 5-HMF after 24 h. 5-HMF, fructose, and inulin gave excellent yields of 5-EMF while, glucose also gave a good yield of 5-EMF. We then turned our attention to use Glu-Fe3O4-SO3H catalyst for sorbitol dehydration to isosorbide (Table 2). Initially, we tried the sorbitol dehydration in water using 10 wt % of catalyst at 120 °C. The starting remained unconsumed even after 12 h. Also when 30 wt % of catalyst was used at 140 °C, no formation of isosorbide was seen. The reaction was then carried out neat at 120 °C and 140 °C under various catalyst concentrations and it was observed that at 140 °C using 20 wt % of catalyst, 94% yield of isosorbide was obtained in 1 h. The isosorbide formation was confirmed by comparing the 1H and 13C NMR data with the reported data in the literature.9 The advantage of this method is that the reaction is carried out neat and no traces of any side products are formed in the reaction. Esterification of oleic acid with methanol was carried out using Glu-Fe3O4-SO3H catalyst under solvent free conditions (Table 3). When 5 wt % of the catalyst was used reaction was completed in 12 h giving 72% yield of methyl oleate. Hence the catalyst concentration was increased to 10 wt % and it was found that the reaction was completed in 4 h at rt giving 99% yield of methyl oleate. We used long chain oleic acid and long chain undecanol for esterification reaction which gave 98% yield of undecyloleate. Finally we also used the catalyst for esterification of acetic acid and long chain undecanol and the reaction gave excellent yield of undecylacetate. In all the above reactions, catalyst was easily separated by external magnetic force. Magnetically separated catalyst was dried at 100 °C for 12 h and reused. The catalyst showed excellent catalytic activity for at least five runs without any significant decrease in the yield of the products (Table 4). In conclusion, the glucose derived magnetic solid acid catalyst Glu-Fe3O4-SO3H has been conveniently studied in 5-EMF formation from 5-HMF and biomass components like fructose, glucose,
Table 1 Study on 5-EMF synthesis EtO
Glu-Fe3O4-SO 3H
5-HMF/Fructose/Glucose/Inulin
O
O
H
ethanol/DMSO:ethanol 5-EMF
a b c
Entry
Starting
Catalyst (wt %)
Temp (°C)
Time (h)
HMFa (%)
EMFa (%)
1 2 3 4 5 6 7 8
5-HMFb 5-HMFb 5-HMFb 5-HMFb Fructoseb Fructoseb Glucosec Inulinc
10 20 30 50 30 50 50 50
80 80 80 80 80 80 140 100
12 8 2 2 24 24 48 24
10 8 — — 10 7 8 10
28 70 92 92 55 81 27 85
Isolated yields. Solvent: ethanol. Solvent: ethanol/DMSO = 2:8.
Table 2 Study on sorbitol dehydration to isosorbide OH
OH OH
HO OH
Glu-Fe3O4-SO 3H
O
neat
OH
OH
O HO H Isosorbide
Sorbitol
a
H
Entry
Catalyst (wt %)
Solvent
Temp (°C)
Time (h)
Isosorbidea (%)
1 2 3 4 5 6
10 30 10 20 20 20
H2O H2O Neat Neat Neat Neat
120 140 120 120 120 140
12 12 5 2 5 1
— — 30 42 89 94
Isolated yields.
Initially we studied the catalytic activity of Glu-Fe3O4-SO3H for etherification of 5-HMF in ethanol (Table 1). The catalyst concentration was studied for the formation of 5-EMF. When 10 wt % and 20 wt % of catalyst was used at 80 °C, 5-HMF was not completely converted to 5-EMF even after prolonged reaction times. 30 wt % of catalyst at 80 °C gave complete conversion of 5-HMF to 5-EMF in 92% yield in 2 h. Further increase in catalyst concentra-
Table 3 Study on esterification of fatty acids O OH
+
Glu-Fe 3O 4-SO 3 H MeOH
neat
Oleic acid
O OMe O
Oleic acid + Undecanol
Glu-Fe 3O 4-SO 3 H
O
neat Undecanol + CH3 COOH
a
C11H 23
O
Glu-Fe 3 O4 -SO 3H O
neat
Entry
Acid
Alcohol
Catalyst (wt %)
Time (h)
Yielda (%)
1 2 3 4
Oleic acid Oleic acid Oleic acid Acetic acid
MeOH MeOH Undecanol Undecanol
5 10 10 10
12 4 5 2.5
72 99 98 98
Isolated yields.
4400
R. S. Thombal, V. H. Jadhav / Tetrahedron Letters 57 (2016) 4398–4400
Table 4 Reuse of Glu-Fe3O4-SO3H catalyst for 5-EMF, isosorbide, and methyl oleate formation Recycle a
EMF Isosorbideb Methyl Oleatec
1st
2nd
3rd
4th
5th
92 94 99
92 94 98
91 94 98
90 93 97
90 92 96
Reaction conditions: (a) HMF (0.1 g), ethanol (5 mL), Glu-Fe3O4-SO3H catalyst (30 wt %), 80 °C, 2 h, (b) Sorbitol (0.25 g), Glu-Fe3O4-SO3H catalyst (20 wt %), neat, 140 °C, 1 h, (c) Oleic acid (0.1 g), methanol (3 mL), Glu-Fe3O4-SO3H catalyst (10 wt %), neat, rt, 4 h.
and inulin. Dehydration of sorbitol to isosorbide and esterification of long chain fatty acids with alcohols gave excellent yields and selectivity. The catalyst was easily separated using external magnetic force and reused at least five times without any significant loss in yield of the products after every recycle. This catalytic system is environmentally friendly and can be used as an ideal method for etherification, dehydration, and esterification reactions in future. Acknowledgements V.H.J. thanks DST, New Delhi for the INSPIRE Faculty Award (IFA 12, CH-44) and Fast Track Grant (CS-041/2013). V.H.J. also thanks Director, NCL for providing all the infra-structural facilities. Supplementary data Supplementary data (detailed experimental procedure, characterization of the products and copies of spectra) associated with
this article can be found, in the online version, at http://dx.doi. org/10.1016/j.tetlet.2016.08.061. References and notes 1. Zhou, C. H.; Xia, X.; Lin, C. X.; Tong, D. S.; Beltramini, J. Chem. Soc. Rev. 2011, 40, 5588–5617. 2. Liu, W. J.; Tian, K.; Jiang, H.; Yu, H. Q. Sci. Rep. 2013, 3, 2419. 3. Wang, H.; Deng, T.; Wang, Y.; Cui, X.; Qi, Y.; Mu, X.; Hou, X.; Zhu, Y. Green Chem. 2013, 15, 2379–2383. 4. Wang, H.; Deng, T.; Wang, Y.; Qi, Y.; Hou, X.; Zhu, Y. Bioresour. Technol. 2013, 136, 394–400. 5. Mascal, M.; Nikitin, E. B. Angew. Chem., Int. Ed. 2008, 47, 7924–7926. 6. Balakrishnan, M.; Sacia, E. R.; Bell, A. T. Green Chem. 2012, 14, 1626–1634. 7. Fenouillot, F.; Rousseau, A.; Colomines, G.; Saint-Loupe, R.; Pascault, J.-P. Prog. Polym. Sci. 2010, 35, 578–622. 8. Rose, M.; Palkovits, R. ChemSusChem 2012, 5, 167–176. 9. Kamimura, A.; Murata, K.; Tanaka, Y.; Okagawa, T.; Matsumoto, H.; Kaiso, K.; Yoshimoto, M. ChemSusChem 2014, 7, 3257–3259. 10. Yamaguchi, A.; Hiyoshi, N.; Sato, O.; Shirai, M. Green Chem. 2011, 13, 873–881. 11. Li, J.; Spina, A.; Moulijn, J. A.; Makkee, M. Catal. Sci. Technol. 2013, 3, 1540–1546. 12. Dabbawala, A. A.; Mishra, D. K.; Huber, G. W.; Hwang, J. S. Appl. Catal. A: Gen. 2013, 456, 168–173. 13. Ahmed, I.; Khan, N. A.; Mishra, D. K.; Lee, J. S.; Hwang, J. S.; Jhung, S. H. Chem. Eng. Sci. 2013, 93, 91–95. 14. Su, F.; Guo, Y. Green Chem. 2014, 16, 2934–2957. 15. Poonjarernsilp, C.; Sano, N.; Sawangpanich, N.; Charinpanitkul, T.; Tamon, H. Green Chem. 2014, 16, 4936–4943. 16. Zhan, S.; Tao, X.; Cai, L.; Liua, X.; Liu, T. Green Chem. 2014, 16, 4649–4653. 17. Do Nascimentoa, L. A. S.; Titoa, L. M. Z.; Angélica, R. S.; Da Costaa, C. E. F.; Zamiana, J. R.; Da Rocha Filho, G. N. Appl. Catal. B: Environ. 2011, 101, 495–503. 18. Son, S. M.; Kimura, H.; Kusakabe, K. Bioresource Technol. 2011, 102, 2130–2132. 19. Thombal, R. S.; Jadhav, V. H. RSC Adv. 2016, 6, 30846–30851.