CHEMSUSCHEM COMMUNICATIONS DOI: 10.1002/cssc.201402794

Synthesis of Cellulose Methylcarbonate in Ionic Liquids using Dimethylcarbonate Sara R. Labafzadeh, K. Juhani Helminen, Ilkka Kilpelinen,* and Alistair W. T. King*[a] Dialkylcarbonates are viewed as low-cost, low-toxicity reagents, finding application in many areas of green chemistry. Homogeneous alkoxycarbonylation of cellulose was accomplished by applying dialkycarbonates (dimethyl and diethyl carbonate) in the ionic liquid-electrolyte trioctylphosphonium acetate ([P8881] [OAc])/DMSO or 1-ethyl-3-methylimidazolium acetate ([emim] [OAc]). Cellulose dialkylcarbonates with a moderate degree of substitution (DS ~ 1) are accessible via this procedure and cellulose methylcarbonate was thoroughly characterized for its chemical and physical properties after regeneration. This included HSQC & HMBC NMR, ATR-IR, molecular weight distribution, morphology, thermal properties, and barrier properties after film formation.

Cellulose, a linear homopolymer consisting of b-(1!4) linked d-glucose units, is the most abundant renewable and biodegradable natural polymer.[1] Cellulose can be chemically converted to a number of polymeric derivatives with remarkable properties, suitable for different applications. The properties of the derivatives depend on the functional group attached to the repeating unit, its regioselectivity within the anhydroglucose unit (AGU) and along the polymer chain, as well as the degree of substitution (DS).[2–5] Among the many cellulose derivatives, cellulose carbonates have been a source of interest and importance over many years. They have found applications as intermediates in the synthesis of aminopolysaccharides via aminolysis, as supports for the delivery of therapeutics, and as imaging agents.[6–10] The first attempts to synthesize stable cellulose carbonates were carried out via the reaction of cellulose with ethyl chloroformate, in the presence of triethylamine as catalyst and DMSO as solvent.[11] Besides the formation of acyclic carbonyl groups, it was demonstrated that trans-2,3-cyclic carbonate formation is also possible in the presence of triethylamine. The cyclic carbonates were further utilized in the reaction with amino and thiol compounds.[12] More recently, a number of innovative approaches were developed for synthesizing the carbonic acid esters of cellulose. N,N-dimethylacetamide (DMA)/LiCl, N,N-dimethylformamide (DMF)/LiCl as well as the ionic liquid 1-butyl3-methylimidazolium chloride ([bmim]Cl) have been reported [a] S. R. Labafzadeh, K. J. Helminen, Prof. Dr. I. Kilpelinen, Dr. A. W. T. King Chemistry Department University of Helsinki A I Virtasen Aukio 1, 00014 (Finland) E-mail: [email protected] [email protected] Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cssc.201402794.

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as suitable solvents to introduce carbonate linkages to cellulose by applying either alkyl or aryl chloroformates, or fluoroformates.[6–8, 13, 14] However, chloroformates are highly reactive reagents. They are known to be decomposed in the presence of nucleophiles under certain conditions. They also lead to the formation of a number of other unexpected species, arising from their high reactivity.[8] When they react in the intended fashion, carbonates are formed alongside hydrochloric acid, which is difficult to recycle from the reaction mixture and can cause degradation of the polymer. When fluoroformates are used, however, the side reactions are minimal and the workup is simple mainly due to the stability of fluoroformates in DMSO and also in tertiary amide solvents.[8, 15] Haloformates are commercially prepared by reacting hydroxy compounds with highly toxic phosgene.[16, 17] They are also expensive. Thus, haloformates are not the reagent of choice for bulk application. Dialkylcarbonates are known as ‘green’ reagents for chemical modifications. Dimethyl carbonate (DMC), for example, is known as a reagent used for methylation and methoxycarbonylation reactions.[18, 19] DMC can be commercially produced through an environmentally friendly route, using O2 as oxidant in presence of CO and methanol.[20] Its catalytic production is also being investigated from methanol and CO2.[21] Importantly the lower homologues of acyclic and cyclic carbonates are of very low toxicity and are biodegradable. In the future they may also be derived from biobased sources, as biomass feedstocks replace petrochemical-based feedstocks (via gasification/CO2 and biofuels). The preparation of polysaccharide carbonates using a broad range of symmetric and asymmetric carbonate esters in the presence of a number of different catalysts, including alkali/alkaline earth metals and organic bases, has been described previously in a German patent. Various molecular solvents or suspending agents have been used but detailed characterization was not performed.[22] Lately, ionic liquids (ILs) have received much attention in cellulose chemistry because of their potential as green solvents dissolution/regeneration applications (e.g. Lyocell), fractionation of lignocellulosic biomass, pretreatments prior to biofuel production and ‘homogeneous’ derivatization.[23, 24] Besides imidazolium-based ILs, which have received enormous attention in many applications, phosphonium IL electrolytes have been recently reported as highly efficient media for the dissolution of lignocellulosic biomass.[25, 26] Compared with ammoniumbased ILs, phosphonium-based ILs typically have higher thermal stability and are inert in most systems, apart from strongly basic conditions. Recent phase-separable versions, which can dissolve cellulose as their electrolytes, form aqueous biphasic systems by addition of water, which could facilitate the recovery or purification of the ILs.[25, 27] In addition, they are suggestChemSusChem 0000, 00, 1 – 5

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CHEMSUSCHEM COMMUNICATIONS ed to be good organocatalysts for the transesterification or methylation organic carbonates with alcohols, including lignin model compounds.[28, 29] As such, the main focus of this work was to assess the potential for modification of cellulose using dialkylcarbonates in novel phase-separable phosphonium electrolyte solutions. Methyltrioctylphosphonium acetate ([P8881][OAc])/DMSO was chosen as the electrolyte.[25] Different alkylcarbonates with varied chain length were chosen as alkoxycarbonylation agents. Finally, the potential of the regenerated derivatives as barriers suitable for packaging industry was studied. Partially substituted cellulose alkylcarbonates were prepared by the homogeneous functionalization of cellulose with dialkylcarbonates in [P8881][OAc]/DMSO. DMC and DEC were applied as alkoxycarbonylating agents (DMC example in Scheme 1). The general procedure for methoxycarbonylation is

www.chemsuschem.org Table 1. Cellulose alkylcarbonates prepared under optimum conditions (5 wt % cellulose in [P8881][OAc]/DMSO (90:10 wt %) and 6 equiv of DMC per AGU) from microcrystalline cellulose (MCC) or Eucalyptus prehydrolysis kraft pulp (PHK). Product

T [8C]

t [h]

DS[a]

Yield[b] [%]

Td[c] [8C]

MW[d] [KDa]

MCC methylcarbonate 1 MCC ethylcarbonate 2 PHK methylcarbonate 3

60 80 60

6 20 6

1.0 1.0 0.9

87 82 89

290 290 270

64 65 168

[a] DS values were determined using a 31P NMR-based method[30] [b] Yields were calculated based on the DS [c] The onset of thermal decomposition [d] Weight average molecular weight were measured using GPC relative to a pullulan calibration.

ing these catalysts (Supporting Information, Figures S6 and S7), suggesting some thermodynamically stable mixture had already been reached under these reagent conditions, in the absence of catalyst. The required temperature and time for attaining maximum DS in the synthesis of cellulose ethylcarbonate Scheme 1. The synthesis of cellulose methylcarbonate from cellulose dissolved in [P8881][OAc]/DMSO and reacted was found to be 80 8C and 20 h. with DMC. Furthermore, we have found that no reaction occurs when cellulose is treated with cyclic as follows: Microcrystalline cellulose (MCC) was initially discarbonates, such as ethylene- or propylene carbonate, at 60 8C solved in a mixture of [P8881][OAc]/DMSO (90:10 wt %) at 90 8C. for up to 20 h (Supporting Information, Figure S8). DEC was After a clear solution was obtained, dimethylcarbonate (6 eq. found to react similarly to DMC, under the same conditions. vs. AGU) was added and the reaction was heated at 60 8C for Methoxycarbonylation of Eucalyptus prehydrolysis kraft pulp 6 h. The products were obtained by the precipitation upon ad(PHK), a higher-molecular-weight dissolving pulp, with DMC dition to methanol. The white precipitate was further washed was also performed under the optimized conditions. Cellulose with methanol and dried under vacuum to yield a white methylcarbonate 3, with only slightly lower DS was obtained powder. The full procedure is given in the Supporting Informafor the PHK sample compared to MCC, indicating that cheaper tion. and higher molecular weight pulp samples are also suitable as Reaction conditions for methoxycarbonylation of cellulose a starting material (Table 1 and Supporting Information, Figwere roughly optimized to maximize DS and obtain high ure S9). 1-Ethyl-3-methylimidazolium acetate ([emim][OAc]), yields. The full optimization results are given in the Supporting a highly effective IL for cellulose dissolution, was also tested to Information. According to ATR-IR analysis of the regenerated investigate whether carbonylation is influenced by a potential products, the maximum DS values were achieved when 5 % of catalytic nature of the phosphonium cation. By comparing the MCC was dissolved in a mixture of [P8881][OAc]/DMSO carbonyl peak intensity of the IR spectra, it was interpreted (90:10 wt %) and the reaction was carried out in the presence that the reaction in the phosphonium IL was only slightly of 6 equiv of DMC per AGU for 6 h, at 60 8C (see Supporting Inmore effective compared to the reaction in [emim][OAc] (Supformation, Figures S1–S5). Actual DS values for representative porting Information, Figure S10). Analysis by 31P NMR also con31 samples (Table 1) were determined using a P NMR-based firmed this. method.[30] It became obvious that the DS of the products did 2D NMR spectroscopy and ATR-IR were used to confirm the formation of cellulose alkylcarbonates. From ATR-IR, the apnot improve by increasing the molar ratio of DMC. In addition, pearance carbonyl stretching frequencies at 1720 cm1 supno complete functionalization was possible, even when applying longer reaction times or higher temperature. It has been ports the introduction of carbonate groups into cellulose demonstrated by Schenzel et al. that the 1,5,7-triazabicy(Figure 1). New peaks at 1260 cm1 and 1446 cm1 appear to clo[4.4.0]dec-5-ene (TBD)-catalyzed transesterification of cellube methyl stretching frequencies from methyl and ethyl funclose, with typically unreactive carboxylate esters, is a highly tionalities on the carbonates 1 and 2, respectively. In order to promising alternative to the conventional esterification procefurther prove the formation of cellulose alkylcarbonates, NMR dures.[31] Thus methoxycarbonylation was performed in the spectroscopy was also applied. The 1H–13C HSQC spectrum for presence of a variety of catalysts, including InBr3, In(OAc)3, MCC methylcarbonate 1 is shown in Figure 2. The HMBC spectrum (Supporting Information, Figure S11) shows the main corAlCl3, TBD, and pyridine during attempts to improve the DS. relation to be between the carbonyl peak in the 13C dimension However, no enhancement of the DS was observed by apply 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Figure 1. ATR-IR spectra of unmodified MCC (solid), MCC methylcarbonate (dashes) and MCC ethylcarbonate (dots).

Figure 2. 1H–13C HSQC NMR spectrum of DS 1 MCC methylcarbonate 1, spectra collected at 90 8C in [D6]DMSO.

www.chemsuschem.org responds quite nicely to typical regioselectivities observed for cellulose esterification under homogeneous conditions C6 > C2 > C3.[32] These were not quantitative HSQC conditions however. The main substituted resonance in the HSQC spectrum is for the C6 geminal protons (66.34:4.30 & 66.34:4.50 ppm). Degradation of the cellulose backbone during the carbonylation reaction was monitored using gel permeation chromatography (GPC). The results suggested that no hydrolysis of cellulose has occurred (Supporting Information, Figure S15). However, the derivatization causes a slight reduction in the molecular weight when PHK is used as a starting material (Supporting Information, Figure S16). The weight average molecular weights (Mw) of samples are presented in Table 1 and the Supporting Information (Table S1). Thermal analysis of the carbonates was evaluated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The onset of thermal decomposition (Td) of the derivatives occurs at a lower temperatures compared to the unmodified celluloses. This is consistent with lower degradation temperatures, due to the absence of crystallinity although the bulk of the material seems to degrade at the same temperature as MCC. The modified MCC and PHK samples degrade at 290 8C and 270 8C, respectively (Table 1, Supporting Information, Figures S17 and S18). No severe thermal instability is introduced although the faster onset of degradation may correspond to the dissociation of carbonate functionalities, or perhaps even crosslinking of carbonate with cellulose hydroxyls. The DSC thermograms for cellulose carbonates are similar to those of unmodified cellulose. No notable phase-transitions are observed for cellulose dialkyl carbonates (Supporting Information, Figures S19 and S20). The prepared MCC carbonates were further analyzed by scanning electron microscopy (SEM) to investigate their morphology and supramolecular structure. The pictures revealed changes in the surface morphology of the derivatives compared to unmodified cellulose (Figure 3 a–b). In contrast to unmodified cellulose a seemingly fibrous or laminar structure exists. It is not clear if this is from incomplete dissolution, prior

(154.59 ppm) and a main peak (3.72 ppm) in the 1H dimension. In the HSQC spectrum the peak at 3.7 does not correlate with any known cellulose resonance, when compared to the resonances for MCC dissolved in [P8881][OAc]/DMSO (60:40 wt %), taken from a previous publicaTable 2. 1H and 13C NMR resonances of MCC methylcarbonate 1 in [D6]DMSO compared to MCC dissolved in tion.[25] [P8881][OAc]/[D6]DMSO electrolyte. Both 1H and 13C resonances MCC in Resonance MCC methylcarbonate for this HSQC correlation are [P8881][OAc]/[D6]DMSO[b] assignment in [D6]DMSO[a] consistent with the methylcar1 13 1 13 C H C H bonate methyl. The DMC methyl CH3 (methyl) 54.45 3.72 – – itself has resonances of 60.28 3.61/3.78 59.71 3.62/3.72 C6[c] 3.79 ppm (COCH3), 54.86 ppm C6S[c] 66.34 4.30/4.50 – – (COCH3), and 156.65 ppm C3 71.94 3.66 75.25 3.21 C2 72.87 3.11 72.92 3.05 (COCH3) in CDCl3. Assignments C5 74.74 3.38 78.36 3.30 for the remaining resonances in 77.54 4.38 – – C2S the HSQC spectrum were made C4 79.40 3.38 74.47 3.40 according to publications by 79.64 4.66 – – C3S 99.69 4.63 – – C1S Holding et al.[20] and Elschner [13] C1 102.26 4.38 102.44 4.35 et al. The peak listings are CO (carbonyl) 154.59 – – – given in Table 2. The relative 1 [a] 100 mg mL , 90 8C, [D6]DMSO. [b] MCC (7.7 wt %) dissolved in [P8881][OAc]/[D6]DMSO (60:40 w/w).[25] [c] gemabundances of the resonances in CH2. the HSQC spectrum for DS 1 cor 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Figure 3. SEM images of a) regenerated MCC methylcarbonate, b) regenerated PHK methylcarbonate, and c–d) MCC methylcarbonate film solvent cast from pyridine.

to modification and regeneration, or supramolecular orientation of the material after regeneration from an isotropic solution. It is also possible that it is simply a result of surface orientation during regeneration from isotropic solutions. This is confirmed by the formation of smooth films after solvent casting (Figure 3 c–d). Cellulose derivatives have found promising applications as packaging films and coatings. The packaging films should provide sufficient mechanical strength and they should also act as moisture and/or oxygen barriers.[33, 34] The potential of the MCC methyl carbonate films as packaging materials was thus examined. The film was prepared by casting the carbonate solution on Teflon plates. The cellulose carbonates have limited solubility in a range of solvents caused most probably by the relatively low DS compared to commercial modified celluloses. A variety of solvents such as DMSO, chloroform, tetrahydrofuran (THF), acetone, toluene and pyridine were tested. No complete dissolution was observed in any of these solvents, aside from DMSO. However, the products demonstrated sufficient solubility in pyridine, as a lower boiling solvent. Thus for practical purposes, the MCC methylcarbonate was dissolved in pyridine and the film was allowed to form upon evaporation of the solvent, from a thin layer of solution applied to the Teflon surface. The films were semitransparent and flexible (Figure 4). As the methyl carbonates were not completely solu-

Figure 4. Cellulose methylcarbonate film.

 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemsuschem.org ble in pyridine, a small fraction of insoluble particles can be observed in the scanning electron microscopy (SEM) images of the films (Figure 3 c–d). Otherwise they displayed a relatively smooth and uniform morphology. The films were also evaluated for their mechanical properties as well as their moisture and oxygen barrier properties. The results showed a value of 35.3 MPa for tensile strength, which is comparable to values obtained for commercial cellulose acetate films (41 MPa).[35] The average elongation value of the films is 4.9 % indicating that they maintain a relatively rigid structure. A Young’s modulus of 2.1 GPa was obtained for the films. Similarly, a value of 1.9 GPa has been reported for films made of cellulose acetate. The films are poor barriers against oxygen as well as water vapor. However, these properties are strongly dependent on the quality of the films prepared using this crude method of preparation. The presence of pinholes or other flaws and the inhomogeneity of the films can result in poor barrier properties. These are initial studies and more accurate methods should be applied in the future. A water vapor permeability (WVP) of around 11.6 (g mm kPa1 m2 d1) was achieved. The poor moisture permeability may be a result of low DS, as the free hydroxyl groups of cellulose play an important role in the pronounced affinity of cellulose for water. DS 1 cellulose methylcarbonate films may show better properties if they are filtered and combined with other polymers or plasticizers. Therefore, they may be used as a component of layered or blended composites. Due to the volatility of the reaction by-product (methanol), starting reactant (DMC) and co-solvent (DMSO), all components should be recyclable in high purity. An integrated process Scheme is shown in the supporting information (Supporting Information, Figure S21). The ionic liquid [P8881][OAc] is also immiscible in water allowing for water washing,[25] to extract water-soluble compounds, for example, saccharide oligomers. Methanol may also be converted back into DMC using catalytic methods from carbon monoxide or carbon dioxide. In the future it is likely that both methanol and carbon monoxide can be produced via syngas, derived from biomass. This would allow for a fully bio-based material with low carbon-footprint. However, we have observed a side reaction between acetate ionic liquids and DMC under the reaction conditions and during recovery of methanol and DMC. It is apparent that under certain conditions the acetate anion reacts with DMC to give methyl acetate. Methyl acetate can be observed in 1H and 13 C NMR spectra of the reaction mixture after the DMC modification step (Supporting Information, Figure S22). This reaction also occurs with [emim][OAc] and not just the phosphoniumbased structure. This is clearly problematic for the sustainability of the process. To avoid this decomposition it was discovered that the work-up of the reaction should be performed under as mild conditions as possible. Therefore, the exact same procedure was followed as before but after the methanol regeneration, the methanol and DMSO were removed, while keeping the temperature of the mixture below 30 8C. This avoids cation decomposition (Supporting Information, Figure S3). This allowed for quantitative recovery of the ionic liquid. Quantitative 1H, HMBC, and HSQC NMR analysis of the ChemSusChem 0000, 00, 1 – 5

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CHEMSUSCHEM COMMUNICATIONS recovered ionic liquid demonstrated consumption of a small portion of the acetate to form a similar quantity of methylcarbonate (Supporting Information, Figures S23–S26). This could then be converted back into the ionic liquid by addition of the appropriate quantity of acetic acid, according to standard anion metathesis reactivity. The properties of the regenerated cellulose methylcarbonate were identical to the previous conditions. Therefore, using the lower temperature regeneration conditions the process can be cycled, without loss of ionic liquid (Figures S23–S26). Other ionic liquids may also facilitate the reaction where the anion is not consumed, for example, 1,3-dialkylimidazolium dialkylphosphates,[36] or chlorides, such as 1-allyl-3-methylimidazolium chloride,[37] or the distillable protic varieties.[38, 39] Functional ionic liquids may also be tuned for the purpose. Conditions may be further optimized to minimize acetate consumption, in particular using catalysts, for example, TBD.[19, 31] This will be the focus of future work. To conclude, cellulose alkylcarbonates with moderate DS values are accessible in [P8881][OAc]/DMSO and [emim][OAc] as reaction medium. Dialkyl carbonates such as dimethyl- and diethyl carbonate were applied as alkoxycarbonylating reagents. This synthesis method employs cheap and non-toxic reagents. There is minimal degradation of the cellulose backbone during modification. Moreover, the functionalization did not significantly reduce the decomposition temperature of cellulose, although at these DS values (DS 1.0) there are no observable glass-transitions or melting points, prohibiting melt processing. At these low DS values it was possible to solvent-cast thinfilms which were flexible and transparent. Although initial barrier properties were not that encouraging, the mechanical properties were similar to cellulose acetate films. DMC is found to react with the carboxylate anion of the ionic liquid and potentially leading to degradation of the cations themselves. However, full recovery of the ionic liquid is possible using milder work-up conditions. There is clear potential for optimization of this reaction to produce cellulose alkylcarbonates, as novel synthons or candidates for high bio-content materials applications.

Acknowledgements Supported by the Finnish Bioeconomy Cluster (FIBIC) as part of the Future Biorefinery (FuBio) Program and the Advanced Cellulose to Novel Products (ACEL) Program. The authors thank Prof. Herbert Sixta and Vahid Jafari for technical support. Keywords: carbonates · cellulose · dimethyl carbonate · ionic liquids [1] T. Heinze, T. Liebert, in Polymer Science: A Comprehensive Reference (Eds.: K. Matyjaszewski, M. Mçller), Elsevier, Amsterdam, 2012, pp. 83 – 152 DOI: 10.1016/B978-0-444-53349-4.00255-7. [2] S. Labafzadeh, J. Kavakka, K. Sievnen, J. Asikkala, I. Kilpelinen, Cellulose 2012, 19, 1295 – 1304.

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www.chemsuschem.org [3] D. Klemm, B. Philipp, T. Heinze, U. Heinze, W. Wagenknecht, in Comprehensive Cellulose Chemistry, Wiley-VCH, 2004, pp. 99 – 145 DOI: 10.1002/ 3527601937.ch1e. [4] S. R. Labafzadeh, J. S. Kavakka, K. Vyavaharkar, K. Sievnen, I. Kilpelinen, RSC Adv. 2014, 4, 22434 – 22441. [5] S. R. Labafzadeh, K. Vyavaharkar, J. S. Kavakka, A. W. T. King, I. Kilpelinen, Carbohydr. Polym. 2014, DOI: 10.1016/j.carbpol.2014.03.077. [6] T. Elschner, K. Ganske, T. Heinze, Cellulose 2013, 20, 339 – 353. [7] A. Pourjavadi, F. Seidi, S. S. Afjeh, N. Nikoseresht, H. Salimi, N. Nemati, Starch/Staerke 2011, 63, 780 – 791. [8] H. Wondraczek, T. Elschner, T. Heinze, Carbohydr. Polym. 2011, 83, 1112 – 1118. [9] S. Oh, D. Yoo, Y. Shin, H. Kim, H. Kim, Y. Chung, W. Park, J. Youk, Fibers Polym. 2005, 6, 95 – 102. [10] C. C. Nam, O. S. Youn, O. Y. Se, P. K. Hoo, P. W. Ho, Y. K. Seung, Y. D. Il, WO 2000 012790, 2000. [11] S. A. Barker, H. Cho Tun, S. H. Doss, C. J. Gray, J. F. Kennedy, Carbohydr. Res. 1971, 17, 471 – 474. [12] J. F. Kennedy, H. Cho Tun, Carbohydr. Res. 1973, 29, 246 – 251. [13] T. Elschner, M. Kçtteritzsch, T. Heinze, Macromol. Biosci. 2013, 13, 161 – 165. [14] M. Fleischer, H. Blattmann, R. Mulhaupt, Green Chem. 2013, 15, 934 – 942. [15] A. Dang Vu Ahn, R. A. Olofson, J. Org. Chem. 1990, 55, 1851 – 1854. [16] M. Matzner, R. P. Kurkjy, R. J. Cotter, Chem. Rev. 1964, 64, 645 – 687. [17] J. Cuomo, R. A. Olofson, J. Org. Chem. 1979, 44, 1016 – 1017. [18] P. Tundo, M. Selva, Acc. Chem. Res. 2002, 35, 706 – 716. [19] H. Mutlu, J. Ruiz, S. C. Solleder, M. A. R. Meier, Green Chem. 2012, 14, 1728 – 1735. [20] M. A. Pacheco, C. L. Marshall, Energy Fuels 1997, 11, 2 – 29. [21] Z.-F. Zhang, Z.-W. Liu, J. Lu, Z.-T. Liu, Ind. Eng. Chem. Res. 2011, 50, 1981 – 1988. [22] K. Szablikowski, H. J. Buysch, A. Klausener, US5484903A, 1996. [23] O. A. El Seoud, A. Koschella, L. C. Fidale, S. Dorn, T. Heinze, Biomacromolecules 2007, 8, 2629 – 2647. [24] M. Gericke, P. Fardim, T. Heinze, Molecules 2012, 17, 7458 – 7502. [25] A. J. Holding, M. Heikkil, I. Kilpelinen, A. W. T. King, ChemSusChem 2014, 7, 1422 – 1434. [26] M. Abe, Y. Fukaya, H. Ohno, Chem. Commun. 2012, 48, 1808 – 1810. [27] K. J. Fraser, D. R. MacFarlane, Aust. J. Chem. 2009, 62, 309 – 321. [28] M. Selva, M. Noe, A. Perosa, M. Gottardo, Org. Biomol. Chem. 2012, 10, 6569 – 6578. [29] J. N. G. Stanley, M. Selva, A. F. Masters, T. Maschmeyer, A. Perosa, Green Chem. 2013, 15, 3195 – 3204. [30] A. W. T. King, J. Jalomki, M. Granstrçm, D. S. Argyropoulos, S. Heikkinen, I. Kilpelinen, Anal. Methods 2010, 2, 1499 – 1505. [31] A. Schenzel, A. Hufendiek, C. Barner-Kowollik, M. A. R. Meier, Green Chem. 2014, 16, 3266 – 3271. [32] T. Heinze, T. Liebert, A. Koschella, in Esterification of Polysaccharides, Springer, Heidelberg, 2006, pp. 53 – 116. DOI: 10.1007/3-540-32112-8 5. [33] J.-W. Rhim, H.-M. Park, C.-S. Ha, Prog. Polym. Sci. 2013, 38, 1629 – 1652. [34] I. Sebti, F. Ham-Pichavant, V. Coma, J. Agric. Food Chem. 2002, 50, 4290 – 4294. [35] S. Paunonen, BioResources 2013, 8, 3098 – 3121. [36] Y. Fukaya, K. Hayashi, M. Wada, H. Ohno, Green Chem. 2008, 10, 44 – 46. [37] J. Wu, J. Zhang, H. Zhang, J. He, Q. Ren, M. Guo, Biomacromolecules 2004, 5, 266 – 268. [38] A. W. T. King, J. Asikkala, I. Mutikainen, P. Jrvi, I. Kilpelinen, Angew. Chem. Int. Ed. 2011, 50, 6301 – 6305; Angew. Chem. 2011, 123, 6425 – 6429. [39] A. Parviainen, A. W. T. King, I. Mutikainen, M. Hummel, C. Selg, L. K. J. Hauru, H. Sixta, I. Kilpelinen, ChemSusChem 2013, 6, 2161 – 2169.

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COMMUNICATIONS S. R. Labafzadeh, K. J. Helminen, I. Kilpelinen,* A. W. T. King* && – && Synthesis of Cellulose Methylcarbonate in Ionic Liquids using Dimethylcarbonate

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The neste-best thing: Cellulose methylcarbonate is prepared in ionic liquid by transesterification with dimethylcarbonate, a cheap and low-toxicity reagent. There is minimal degradation of the cellulose backbone during modification. Its chemical, mechanical, and barrier properties are determined, revealing the material’s potential as a fully biobased polymer for future applications.

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Synthesis of cellulose methylcarbonate in ionic liquids using dimethylcarbonate.

Dialkylcarbonates are viewed as low-cost, low-toxicity reagents, finding application in many areas of green chemistry. Homogeneous alkoxycarbonylation...
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