Acidic Ionic Liquid Catalyzed Liquefaction of Cellulose in Ethylene

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Acidic ionic liquid catalyzed liquefaction of cellulose in ethylene glycol; identification of a new cellulose derived cyclopentenone derivative Ananda Sarath Amarasekara Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie504544s • Publication Date (Web): 26 Dec 2014 Downloaded from http://pubs.acs.org on January 8, 2015

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Acidic ionic liquid catalyzed liquefaction of cellulose in ethylene glycol; identification of a new cellulose derived cyclopentenone derivative

Journal: Manuscript ID: Manuscript Type: Date Submitted by the Author: Complete List of Authors:

Industrial & Engineering Chemistry Research ie-2014-04544s.R1 Article 22-Dec-2014 Amarasekara, Ananda; Prairie View A&M University, Chemistry Wiredu, Bernard; Prairie View A&M University, Chemistry

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Acidic ionic liquid catalyzed liquefaction of cellulose in ethylene glycol; identification of a new cellulose derived cyclopentenone derivative Ananda S. Amarasekara* and Bernard Wiredu Department of Chemistry, Prairie View A&M University, Prairie View, Texas 77446, USA E-mail: [email protected] Tel: +1 936 261 3107; fax: +1 936 261 3117

_______________________________________________________________________________

ABSTRACT: Cellulose can be liquefied in ethylene glycol at 180 °C, using 6.7 mol % 1(1-alkylsulfonic)-3-methylimidazolium chloride ionic liquids as catalysts. The maximum liquefied product yields of 0.3436 and 0.3046 g/g of cellulose were achieved after 20 h at 180 °C using 1-(1-proylsulfonic)-3-methylimidazolium chloride and 1-(1-butylsulfonic)3-methylimidazolium chloride as the catalysts. The liquefied oil produced from both ionic liquid catalysts had similar compositions. Unlike in previously reported mineral acid catalyzed cellulose liquefactions, the new catalysts gives stable oils with well defined compositions of only three compounds. The three compounds in the oil were identified as 2-hydroxyethyl levulinate, 2-hydroxyethyl levulinate ethylene ketal and 2,3,6,7-tetrahydrocyclopenta[1,4]dioxin-5-one using GC-MS, HRMS, 1H,

13

C and 1H-1H COSY NMR

spectroscopy. The third product 2,3,6,7-tetrahydro-cyclopenta[1,4]dioxin-5-one is a new C-6 carbohydrate derived cyclopentenone derivative; identified for the first time in a cellulose liquefaction process. The composition of the three components reaches a steady state after 20 h reaction at 180 °C with 2-hydroxyethyl levulinate : 2-hydroxyethyl levulinate

ethylene

ketal

:

2,3,6,7-tetrahydro-cyclopenta[1,4]dioxin-5-one

molar

percentage ratio of approximately 47: 22 : 31. ________________________________________________________________________

KEYWORDS: cellulose, acidic ionic liquid, ethylene glycol, liquefaction, cyclopentenone



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1. Introduction Current efforts in the development of next generation technologies to utilize non-food biomass resources for renewable fuels and chemical feedstocks cover a wide range of paths.

These

approaches

include;

cellulosic-ethanol1,

bio-oil2,3,

algae-biodiesel4,

liquefaction of biomass under acidic/basic/hydrothermal conditions5,6, gasification of biomass to syn-gas followed by conversion to fuels/feedstocks using chemical catalytic methods7,8 or enzymatic routes9,10 and synthetic approaches based on biomass derived furan aldehydes11,12. Liquefaction of biomass is one of the major paths in this wide field, and can be carried out in water or in solvents like phenol13, ethanol, 1-octanol14, polyhydric alcohols, and ethylene carbonate15 with or without catalysts like AlCl316.

A number of

raw biomass forms; corn stover, wheat straw and bamboo have been liquefied in these solvents17,18,19. Hydrothermal liquefaction is the most widely studied variant due to attractiveness of using water as the solvent and generally carried out at harsh conditions like temperatures around 280-370 °C, and pressures between 10 to 25 MPa6. The main products of hydrothermal liquefaction are biocrude oil with a relatively high heating value, char, water-soluble substances and gases. Additionally, oil quality in this process can be improved by adding catalysts as well. One particularly interesting example is the use of SO3H-, COOH- functionalized and HSO4- paired imidazolium ionic liquids as catalysts for bagasse liquefaction in hot compressed water20. In this example, Long and co workers reported a 96.1% liquefaction of bagasse at 543 K and 50.6% was selectively converted to low-boiling biochemicals. The product analysis and comparative characterization of raw materials and residues led to the suggestion that both catalytic liquefaction and hydrolysis processes contributed to the high conversion of bagasse. A possible liquefaction mechanism based on the generation of 3-cyclohexyl-1-propanol, one of the main products is also proposed during this work20.

Yamada et al. has liquefied cellulose in phenol as well as in water and found that the products were mainly 5-hydroxymethylfurfural, glucose and oligosaccharides21. Later the same group studied the liquefaction of cellulose in ethylene glycol and in ethylene carbonate22,15. In ethylene glycol liquefaction studies the cellulose liquefied oils were separated to chloroform and water soluble fractions; monosaccharides and ethylene glycol-


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3 glycosides were found in the water layer. Whereas, formic acid, levulinic acid and 2hydroxyethyl levulinate were found in the chloroform layer. A few researchers have recently recognized the excellent biomass solubilizing capacity of ethylene glycol, where they have studied liquefaction using H2SO4, H3PO423,24,25, and organic acids such as oxalic acid26, formic acid27 as catalysts at moderate temperatures around 190 °C. Zhang et al. has recently reported the liquefaction of sugar cane bagasse in ethylene glycol, catalyzed by H2SO4 at 190 °C under atmospheric pressure. During these studies, diethylene glycol, ethylene glycol derivatives of sugars, alcohols, aldehydes, ketones, phenols, formic acid, levulinic acid, acetic acid, oxalic acid, 2-hydroxy-butyric acid and their esters were identified as key compounds in the liquefied product28. In another example, Yip and co workers reported a HCl catalyzed liquefaction of bamboo in ethylene glycol at 180 °C, where they have been able to identify 26 compounds in the liquefied oil by GC-MS qualitative analysis29. The main draw back in biomass liquefaction studies are harsh conditions used, formation of complex intractable mixtures, often with unstable compounds; many studies failed to identify the compounds in the liquefied products and the few studies reporting GC-MS library matching identifications failed to provide any quantitative analysis of the mixture. Since 2009 we have been exploring the sulfonic acid group functionalized acidic ionic liquids30,31,32, immobilized acidic ionic liquid catalysts33, as well as alkyl/aryl sulfonic acids34 as catalysts for the depolymerization of cellulose and lignocellulosic biomass for biofuel applications. Where we first reported that Brönsted acidic ionic liquid (BAIL) like 1-(1-propylsulfonic)-3-methylimidazolium chloride can be used as an acid catalysts for the depolymerization of cellulose dissolved in the ionic liquid itself30 as well as in aqueous solutions31. As far as we are aware the application of these acidic ionic liquid catalysts in the liquefaction of biomass in polyhydric alcohols is not reported in the literature, and in this publication we are reporting the first use of 1-(1-alkylsulfonic)-3-methylimidazolium chloride acidic ionic liquids (figure 1.) as catalysts for the liquefaction of cellulose in ethylene glycol as shown in figure 2.



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2. Experimental 2.1. Materials and Instrumentation Sigmacell cellulose - type 101 (DP ~ 450, from cotton linters), 1-methylimidazole, 1,3propanesultone, 1,4-butanesultone, ethylene glycol (reagent plus grade 99%, with 1% water) were purchased from Aldrich Chemical Co. BAIL catalysts were prepared by condensation of 1-methylimidazole with 1,3-propanesultone or 1,4-butanesultone and acidification of the resulting salts with conc. HCl according to the literature procedure as shown in figure 135,36. Cellulose liquefaction experiments were carried out in 25 mL stainless steel solvothermal reaction kettles with Teflon inner sleeves, purchased from Lonsino Medical Products Co. Ltd. Jingsu, China. These reaction kettles were heated in a preheated Precision Scientific model-28 laboratory oven with temperature accuracy ±1 °C. The cellulose liquefied products were concentrated using a Buchi R-II rotary evaporator under reduced pressure of 30 mmHg and a room-temperature water bath. The products were first analyzed by low resolution mass spectra recorded using a Varian 3900/ Saturn 2100T GC/MS system; carrier gas flow rate 1.0 mL min-1, split ratio 1:20, injector temperature of 180°C, with Saturn GC/MS WS Ver. 5.5 Software and NIST 98 Library. High resolution mass spectra were recorded using a MDS Sciex API QStar Pulsar - hybrid quadrupole/time-of-flight instrument with electro spray ionization (ESI). 1H NMR Spectra were recorded in CDCl3 on a Varian Mercury plus spectrometer operating at 400 MHz and chemical shifts are given in ppm downfield from TMS (δ = 0.00). 13C NMR were recorded in the same spectrometer at 100MHz, and chemical shifts were measured relative to CDCl3 and converted to δ (TMS) using δ (CDCl3) = 77.00.

2.2. General procedure for 1-(1-alkylsulfonic)-3-methylimidazolium chloride ionic liquid catalyzed liquefaction of cellulose in ethylene glycol

A mixture of Sigmacell cellulose-type 101 (DP ~ 450) (0.500 g, 3.086 mmol of glucose units of cellulose), catalyst (3a or b, 0.208 mmol, 6.7 mol %) and 4.00 mL of ethylene glycol was prepared in a 25 mL high pressure stainless steel reaction kettle with Teflon inner sleeve. The reaction kettle was firmly closed and heated in a thermostated oven


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5 maintained at 180±1 °C for a specified length of time. Then reaction kettle was removed from the oven and immediately cooled under running cold water to quench the reaction. The liquefied product was diluted with 25 mL of deionized water and repeatedly extracted with methylene chloride (3 X 10 mL), combined organic layer was dried over anhydrous Na2SO4 and concentrated under reduced pressure to give cellulose liquefied product as a dark viscous oil. The aqueous layer was centrifuged at 1,700 g for 5 min, to remove the suspended solids; residue was washed with water (2X 4mL), dried in an oven at 90 °C for 24 h and weighed to determine the solid residue. The weights of cellulose liquefied products and solid residues produced from a series of experiments carried out for 5-25 h at 180 °C using BAIL catalysts 3a and b are shown in figures 3a and 3b respectively.

2.3. Qualitative analysis of the products in the cellulose liquefied product The oil products were analyzed using GC-MS and NMR spectroscopy to identify the compounds present. These experiments revealed that three main products are formed in the liquefaction. The total amount of all minor products was estimated as < 1% using 1H NMR spectroscopy, as the total integration of all minor products is less than 1% of the sum of the integration of the three identified compounds. A representative GC-MS, 1H and 13C NMR spectra from cellulose liquefaction oil produced after 20 h reaction at 180 °C using catalyst 3a are shown in figures 4 and 5a,b respectively. Analysis of these spectra showed that the oil composed of previously reported compounds 2-hydroxyethyl levulinate (5), 2hydroxyethyl levulinate ethylene ketal (6) as shown in figure 2 and an unknown compound. The two known compounds were identified by comparison of the 1H and

13

C

NMR spectra with literature data37,38. 1H-1H COSY spectrum further supported the analysis and the partial 1H-1H COSY spectrum showing the 1.96-3.00 ppm region is shown in figure 6.



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6 2.4. Isolation of the new compound in the cellulose liquefied product In order to identify the new compound, a 100 mg portion of the cellulose liquefied oil produced during 3a catalyzed liquefaction of cellulose in ethylene glycol for 20 h was chromatographed on a silica column eluting with 1:1 ethyl acetate : methylene chloride as the solvent. The fractions were analyzed by thin layer chromatography (silica, 1:1 ethyl acetate : methylene chloride) and the fractions showing a 254 nm light UV active spot with Rf = 0.40 were combined and evaporated to remove the solvent, yielding 25 mg of 7 as a viscous oil. The attempts to crystallize the oil by cooling to -15 °C overnight were not successful. The 1H and

13

C NMR spectra of 7 recorded in CDCl3 are shown in figure 7a

and b respectively. Complete physical data of the new compound 7: UV (MeOH) λmax 264 nm. IR (neat) 665, 867, 1078, 1132, 1182, 1247, 1236, 1406, 1460, 1646, 1711, 2933 cm-1. 1H NMR (CDCl3) δ 2.40 (2H, m, CH2-CO), 2.56 (2H, m, CH2-C=), 4.09 (2H, m, CH2-O), 4.28 (2H, m, CH2-O).

13

C NMR (CDCl3) δ 22.6 (C-7), 30.6 (C-6),

63.7 (C-2/3), 66.7 (C-2/3), 134.2 (C-4'), 165.7 (C-7'), 194.8 (C-5). HRMS calcd. for +

C7H8O3 [M+H] 141.0552, found: 141.0549.

2.5. Quantitative analysis of the composition of the cellulose liquefied oil Cellulose liquefied oil produced by heating cellulose in ethylene glycol for different time intervals 5.0, 10.0, 15.0, 20.0 and 25.0 h were analyzed by 1H NMR spectroscopy. A representative 1H NMR spectrum from liquefaction oil produced after 20 h reaction at 180 °C using catalyst 3a is shown in figure 5a. The compositions of liquefied oils were analyzed by integration of 1H NMR methylene group peaks at 2.79, 2.08, and 2.56 ppm from compounds 5, 6 and 7 respectively. The molar composition variations of 5, 6 and 7 produced during ionic liquid 3a catalyzed liquefaction process is shown in figure 8.


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7

3. Results and Discussion

3.1. Cellulose liquefaction Imidazolium type sulfonic acid group functionalized BAILs 1-(1-alkylsulfonic)-3methylimidazolium chlorides 3a and b were chosen as the catalysts for cellulose liquefaction study because our earlier studies have shown that these functionalized ionic liquids are better catalysts than pyridinium and triethanol ammonium cation based acidic ionic liquids with built-in sulfonic acid groups for the challenging cellulose depolymerization step in the reaction sequence30. In addition, our earlier studies have shown that 1-(1-propylsulfonic)-3-methylimidazolium chloride is a better catalyst than sulfuric acid of the same acid strength for the degradation of cellulose to glucose and oligomers in neat and in aqueous medium in short reaction time (1-3 h) experiments31. BAIL catalysts 3a,b used in this work were prepared by condensation of 1methylimidazole (1) with 1,3-propanesultone (2a) or 1,4-butanesultone (2b) and acidification of the resulting salts with conc. HCl, as shown in figure 1, according to the literature procedure35,36. A preliminary experiment carried out with half the catalyst loading used in this study produced much lower oil yields, and higher catalyst loadings resulted excessive charring. Therefore, a catalyst loading of 6.7% was selected for the present study. In addition, all the experiments in this study were carried out at 180 °C, since our previous studies on direct conversion of cellulose to ethyl levulinate in alcohols using the same acidic ionic liquid catalysts produced optimum yields under similar conditions39. In cellulose liquefaction experiments Sigmacell cellulose (DP ~ 450) samples with BAIL catalysts 3a,b were heated at 180 °C in ethylene glycol medium using stainless steel solvothermal reaction kettles for 5-25 h. The hydrophobic oil product formed was separated from BAIL catalyst by solvent extraction after dilution of the reaction mixture with water. The solid residue formed was isolated by centrifugation as described in the sections 2.2. The changes in cellulose liquefied oil/sold residue weights during 1-(1-proylsulfonic)-3-methylimidazolium chloride (3a) and 1-(1-butyllsulfonic)-3-methylimidazolium chloride (3b) catalyzed liquefaction experiments are shown in the plots in figures 3a and 3b. These experiments



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8 show that cellulose liquefied oil yield increases up to about 20 h and the yield decreases beyond 20 h in both ionic liquids. The maximum liquefied product yields of 0.3436 and 0.3046 g/g of cellulose were achieved after 20 h at 180 °C using 1-(1-proylsulfonic)-3methylimidazolium chloride and 1-(1-butylsulfonic)-3-methylimidazolium chloride as catalysts. The solid residue weights rapidly drops in the first 5 h in both experiments showing that initial dehydration of sugars are complete during this period and reaches a steady state after about 15 h.

3.2. Analysis of the products in the cellulose liquefied product Cellulose liquefied oils prepared were first analyzed using GC-MS; the oils produced using both catalysts 3a,b showed similar composition profiles and showed three major compounds in all samples. Representative GC-MS total ion current (TIC) chromatogram of cellulose liquefied oil produced during 1-(1-proylsulfonic)-3-methylimidazolium chloride catalyzed liquefaction of cellulose in ethylene glycol for 20 h is shown in figure 4, indicating the m/z of M+ ion in each component. The three main components in oil indicated molecular ion peaks at m/z = 160, 140 and 204. In order to identify the three compounds, the liquefied product samples were further analyzed by NMR spectroscopy. A representative 1H (a) and

13

C NMR (b) spectra (in CDCl3) of cellulose liquefied oil

produced during 1-(1-proylsulfonic)-3-methylimidazolium chloride catalyzed liquefaction of cellulose in ethylene glycol for 20 h is shown in figure 5. The 1.00-3.00 ppm high field region of the 1H NMR spectrum showed two singlets, four triplets and two multiplets. The coupling pattern of these peaks were resolved by recording 1H-1H COSY spectrum and partial COSY spectrum in the 1.96-3.00 ppm region is shown in figure 6. The COSY spectrum showed three cross peaks in the 1.96-3.00 ppm region, arising from the coupling of three pairs of signals: triplets at 2.08, 2.43; triplets at 2.61, 2.79 and multiplets at 2.40, 2.56 ppm indicating the three compounds in the mixture (figure 6). 13

C NMR spectrum of the same sample showed 22 peaks: 8 peaks in the 10-40 ppm region,

7 peaks in the 60-70 ppm region and 7 peaks in the low field (100-220 ppm) (figure 5b). The eight peaks in the low field were identified as two methyl groups and six methylene


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9 groups using attached proton test (APT) experiment (not shown). Additionally APT experiment helped to identify the seven peaks in the 60-70 ppm region as seven methylene groups, whereas the seven peaks in the 100-220 ppm region are due to quaternary carbons. Further analysis of the

13

C spectrum revealed that 15 out of 22 carbon signals in the

spectrum are due to two levulinic acid derivatives. These previously reported compounds were identified as 2-hydroxyethyl levulinate (5) and 2-hydroxyethyl levulinate ethylene ketal (6) (figure 2) by comparison of 1H and 13C NMR data with literature values37,38.

3.3. Identification of the new compound 7 In order to identify the third compound we have isolated this compound from the product mixture using column chromatography, and the isolation of the new compound was further facilitated by the fact that this compound exhibited a bright blue spots when visualized under 254 nm UV light during the thin layer chromatographic analysis (TLC plates with a fluorescent indicator) of the column chromatography fractions. Since we have already identified two components in the mixture, the GC-MS TIC peaks indicating M+ with m/z 160 and 204 could be assigned to 2-hydroxyethyl levulinate (5) and 2-hydroxyethyl levulinate ethylene ketal (6). The remaining GC-MS TIC peak with molecular ion m/z = 140 mass units was assigned to the new compound 7. The high resolution mass spectrum further confirmed this analysis, where [M+H]+ HRMS peak at 141.0549 mass units (calculated: 141.0552) predicted the formula as C7H8O3. In addition, 1H NMR of 7 showed four multiplets at 2.40, 2.56, 4.09 and 4.28 ppm (figure 7a). The peaks at 2.40 and 2.56 ppm could be assigned to methylene groups next to C=O or C=C groups, where as the peaks 4.09 and 4.28 ppm are due to methylene groups next to oxygen atoms (-CH2-O-). 1

H-1H COSY spectrum indicated that CH2 groups at 2.40 and 2.56 ppm are coupled each

other (figure 6). Additionally, the same COSY experiment suggested that coupled peaks at 4.09 and 4.28 ppm are due to an asymmetrically substituted -O-CH2-CH2-O- system in the molecule.



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C NMR spectrum of 7 showed seven peaks (figure 7b) and the APT spectrum of 7 (not

shown) indicated that high field peaks at 22.6, 30.6, 63.7 and 66.7 ppm are due to four methylene groups. Whereas low field peaks at 134.2, 165.7 and 194.8 ppm are from three quaternary carbons, and most likely representing a α,β-unsaturated carbonyl system. The fragments identified form 1H,

13

C, 1H-1H COSY and APT

NMR data were used to

formulate the structure to be identified as 2,3,6,7-tetrahydro-cyclopenta[1,4]dioxin-5-one (7) (figure 2). A comparison of the spectroscopic data with similar known compounds further confirmed the structure40,41. For instance, 6-isopropyl derivative of 2,3,6,7tetrahydro-cyclopenta[1,4]dioxin-5-one is known to give 13C peaks at 63.84, 66.80, 134.31, 165.08, and 196.92 ppm for C-2/3, 4', 7', and 540. The corresponding carbons of 7 showed peaks at 63.7, 66.7, 134.2, 165.7 and 194.8 ppm further confirming our structure. IR Spectrum of 7 showed peaks at 1711 and 1646 cm-1 due to C=O group and conjugated C=C in the α,β-unsaturated carbonyl system. These absorptions are comparable to the IR absorptions reported at 1707 and 1641 cm-1 for an α,β-unsaturated carbonyl system in 6isopropyl,

2,3,6,7-tetrahydro-cyclopenta[1,4]dioxin-5-one40. The UV spectrum of 8

recorded in methanol showed a λmax at 264 nm; in addition, we have compared this value with theoretically predicted UV absorption maximum for this type of chromophores. The Woodward-Fieser rules based λmax calculation for a cyclopentenone α,β-unsaturated carbonyl function with two oxygen substituent groups (-OR) at α and β carbons predicts the λmax at 267 nm, and this analysis also confirms our proposed structure42.

3.4. Composition variations of the cellulose liquefied product The variation in composition of the cellulose liquefied product was studied as described in experiment 2.5. Composition variations of the three products 5, 6 and 7 produced during the ionic liquid 3a catalyzed process is shown in figure 8. This experiment revealed that products 6 and 7 are produced rapidly in the first 5 h of the reaction, whereas compound 5 shows a relatively lower yield after 5 h. However, the reaction reaches an equilibrium state after 20 h, and molar percentage composition of 2-hydroxyethyl levulinate (5) : 2-


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11 hydroxyethyl levulinate ethylene ketal (6) : 2,3,6,7-tetrahydro-cyclopenta[1,4]dioxin-5-one (7) is approximately 47: 22 : 31 at the equilibrium stage of the reaction.

3.5. Proposed reaction pathway for the formation of products 5, 6 and 7 The proposed reaction pathway for the formation of the three products 5, 6, and 7 is shown in figure 9. Acidic ionic liquid catalyzed hydrolysis of cellulose leads to glucose and this depolymerization is facilitated by polar interactions between imidazolium chloride structure and hydroxyl groups of cellulose30,31. The solvent used is 99% ethylene glycol with 1% water and this medium provides the controlled amount of water required for the hydrolysis step. Then acid catalyzed isomerization of glucose to fructose leads to the dehydration to 5-hydroxymethylfurfural (5-HMF) as shown in earlier mechanistic studies43,44. In the next stage 5-HMF formed can undergo a rehydration followed by a fragmentation, eliminating formic acid to yield the intermediate 8 as proposed by Horvat and co-workers45. This intermediate can either isomerize to levulinic acid (LA) or undergo an acid catalyzed cyclization to give 4-hydroxy-cyclopentenone. The levulinic acid formed can undergo an acid catalyzed esterification with ethylene glycol (4) to give 5, and further reaction with ethylene glycol at the carbonyl group, following acid catalyzed ketalization mechanism leads to 6. The 4-hydroxy-cyclopentenone formed can also react with ethylene glycol, resulting a cyclization to give 2,3,4',6,7,7'-hexahydro-cyclopenta[1,4]dioxin-5-one intermediate under acid catalysis conditions. The oxidation of this hexahydrocyclopenta[1,4]dioxin-5-one system with atmospheric oxygen in the reactor may lead to the more stable product: 2,3,6,7-tetrahydro-cyclopenta[1,4]dioxin-5-one (7). This is the first report of compound 7 and original finding of the formation of tetrahydrocyclopenta[1,4]dioxin-5-one ring system during a cellulose liquefaction process. In addition, we have studied the possibility of recovering and recycling the ionic liquid catalyst. These experiments revealed that all the liquefied oil produced can be recovered from the water phase and highly polar acidic ionic liquid catalyst and excess ethylene glycol remains in the aqueous phase during the solvent extraction separation process due to distinct polarity differences between the catalyst and the products formed.



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4. Conclusion We have shown that 1-(1-alkylsulfonic)-3-methylimidazolium chloride ionic liquid catalysts can be used to liquefy cellulose in ethylene glycol at 180 °C to produce hydrophobic liquefied oils. Unlike in the previously reported cellulose liquefactions using mineral acids, the new ionic liquid catalyst system is able to produce a stable liquefied oil with a well defined composition of merely three compounds. The liquefied oil produced from both catalysts: 1-(1-proylsulfonic)-3-methylimidazolium chloride and 1-(1butylsulfonic)-3-methylimidazolium chloride showed similar compositions and yields. The three compounds in the oil were identified as 2-hydroxyethyl levulinate, 2-hydroxyethyl levulinate ethylene ketal and 2,3,6,7-tetrahydro-cyclopenta[1,4]dioxin-5-one using GCMS, HRMS, 1H,

13

C and 1H-1H COSY NMR spectroscopy. The composition of the three

components reaches a steady state after 20 h reaction at 180 °C with 2-hydroxyethyl levulinate

:

2-hydroxyethyl

levulinate

ethylene

ketal

:

2,3,6,7-tetrahydro-

cyclopenta[1,4]dioxin-5-one, molar percentage ratio of approximately 47: 22 : 31. This is the first example of producing a well defined simple product mixtures and identification of a cyclopentenone derivative in a cellulose liquefaction process.

Acknowledgments Authors would like to thank the National Science Foundation (NSF) (through Grant Nos. CBET-0929970, CBET-1336469, HRD-1036593), and the U.S. Department of Agriculture (USDA) (through Grant No. CBG-2010-38821-21569) for financial support.


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13

O H3C

N

1. 80 C, 16 h

O S O

N

_ Cl

o

H3C

o

+

n

SO3H

2. HCl, 23 C, 24 h

n

1

N + N

3a, n = 1

2a,b

3b, n = 2

Fig. 1.

O O O O Cellulose

glucose

(DP ~ 450)

OH

O

O

CHO

O

_ Cl

H 3C

N + N

Reaction conditions:

n

SO3H

3a, n = 1 3b, n = 2

HO

OH 4

O O

O

o

180 C, 5-25 h

Fig. 2.


OH 5

OH 6

O

7


14

liquefied oil/residue weight (g) per 1.000 g of cellulose

(a) 1

0.8

0.6

residue liquefied oil

0.4

0.2

0 0

5

10

15

20

25

Time (h)

(b)

liquefied oil/residue weight (g) per 1.000 g of cellulose

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 25

1

0.8

0.6

residue liquefied oil

0.4

0.2

0 0

5

10

15

20

25

Time (h)

Fig. 3.


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15

Fig. 4.



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16

Fig. 5.


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17

Fig. 6.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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18

Fig. 7.


Page 19 of 25

19 50

40 Molar composition (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


30

20 5 6 7

10

0 0

5

10

15

20

25

Time (h)

Fig. 8.



20 OH

Cellulose

HO HO

(DP ~ 450)

OH O

OH OH

OH

OH

O HO

- H2 O

OH

OH Fructose

Glucose

- H2O

+

+ OH2

H

OH CHO

O

OH O

- H 2O

OH CHO

OH O

OH

OH

O

+O

OH CHO

O

CHO

OH

- H 2O

:

+H

OH CHO

OH

CHO

5-HMF H 2O

OH

O HO

OH

H

:

OO

CHO

CHO

OO

H

+ 2H2O O OH O HO

O

LA +

H

OH

O H

8 HO 4

O

O O

OH

H

OH

OH +

O

: OH

H OH OH

O

OH OH HO

+

:

HO

5

+

- H 2O

OH2 OH

O +

OH

H

+

H

HO

OH

O

O

O O

+

HO

4

OH2

:

HO

OH 6

O

O

[O]

O 7

O

OH 4

O

O

Fig. 9.


HO

:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 25

OH O

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21 Figure Captions Fig. 1. Preparation of 1-(propylsulfonic)-3-methylimidazolium chloride (3a) and 1(butylsulfonic)-3-methylimidazolium chloride (3b) BAILs Fig. 2. BAIL 1-(1-alkylsulfonic)-3-methylimidazolium chloride (3a,b) catalyzed liquefaction of cellulose in ethylene glycol Fig. 3. The changes in cellulose liquefied oil/ sold residue weights (g) per 1.000 g of cellulose during 1-(1-proylsulfonic)-3-methylimidazolium chloride (a) and 1-(1butylsulfonic)-3-methylimidazolium chloride (b) ionic liquid catalyzed liquefaction of cellulose in ethylene glycol. 0.500 g of Sigmacell cellulose (DP ~ 450) and 6.7 mol % 1(1-alkylsulfonic)-3-methylimidazolium chloride in 4.00 mL ethylene glycol were used in all experiments. All samples were heated at 180 °C. Average values of duplicate experiments are shown. Fig. 4. Representative GC-MS total ion current (TIC) chromatogram of cellulose liquefied oil produced during 1-(1-proylsulfonic)-3-methylimidazolium chloride (3a) catalyzed liquefaction of cellulose in ethylene glycol for 20 h. showing the m/e of M+ ion in each component Fig. 5. Representative 1H (a) and 13C (b) NMR spectra (CDCl3) of cellulose liquefied oil produced during 1-(1-proylsulfonic)-3-methylimidazolium chloride (3a) catalyzed liquefaction of cellulose in ethylene glycol for 20 h. * Solvent Fig. 6. 1.96-3.00 ppm region of 1H-1H COSY spectrum (CDCl3) of cellulose liquefied oil produced during 1-(1-proylsulfonic)-3-methylimidazolium chloride (3a) catalyzed liquefaction of cellulose in ethylene glycol for 20 h Fig. 7. 1H (a) and 13C NMR (b) spectra (CDCl3) of cyclopenta[1,4]dioxin-5-one (7). * Solvent

2,3,6,7-tetrahydro-

Fig. 8. The changes in the molar percentage composition of three products: 2-hydroxyethyl levulinate (5), 2-hydroxyethyl levulinate ethylene ketal (6) and 2,3,6,7-tetrahydrocyclopenta[1,4]dioxin-5-one (7) in cellulose liquefied oil during 1-(1-proylsulfonic)-3methylimidazolium chloride (3a) ionic liquid catalyzed liquefaction of cellulose in ethylene glycol at 180 °C. 0.500 g of Sigmacell cellulose (DP ~ 450) and 6.7 mol % 3a in 4.00 mL ethylene glycol were used in all experiments. Average values of duplicate experiments Fig. 9. Proposed reaction pathways for the formation of three products: 2-hydroxyethyl levulinate (5), 2-hydroxyethyl levulinate ethylene ketal (6) and 2,3,6,7-tetrahydrocyclopenta[1,4]dioxin-5-one (7)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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22

References 1.

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Acidic Ionic Liquid Catalyzed Liquefaction of Cellulose in Ethylene

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