A study of cellulose dissolution in ionic liquid-

water brines

WeiqingSu

StudentDegreeThesisinChemistry45ECTSMaster’sLevelReportpassed:2012‐08‐02Supervisors:Prof.J.‐P.Mikkola&Dr.DilipRaut

I

Abstract

A series ofmorpholinium saltswereprepared in order to investigate their efficacy indissolution of cellulose. These ionic liquids were prepared under normal bench‐topexperimentalconditionsrenderingtheseionicliquidswellsuitedforappliedresearchinindustrial scale. Most of the ionic liquids prepared were halide free, but containedapproximately 60000 ppm water due to their hygroscopicity. It was found that[AMMorp][OAc]‐brineand[AMMorp][HSO4]‐brine,at1200Cin20min,candissolve26wt% and 8 wt% cellulose, respectively. In case of [BMMorp][OAc], [BMMorp][OAc]‐brine was not able to dissolve cellulose and addition of some amount of halogen‐containing ionic liquid was required to dissolve cellulose. The combination of 70%[BMMorp][OAc]with23.3%[BMMorp][Br]and6.7wt%waterenabledthedissolutionof 6 wt% cellulose without any pretreatment, at 80 0C for 24 h. Similarly, 86.7 %[BnMMorp][OAc]with 7% [BnMMorp][Cl] and 6.3wt%water could dissolve 22wt%cellulose at 120 0C in 20min. The organic electrolytic solutions of ionic liquids withvariousinvestigatedaminescouldnotdissolvecelluloseathightemperature,whilethesolutions containingethanol and2‐butanol coulddissolve2wt%and4wt%celluloserespectivelyat700Cin24h.Theopticalmicroscopyimagesunraveledthebehaviorofcellulosic fibers in different solvent systems. Importantly, recovered ionic liquid stillshowedastrongabilityfordissolutionofcellulose.Duetotheirefficacyindissolutionofcelluloseinthepresenceofhighamountofwater,theseionicliquidscanbepotentiallyappliedinindustryforprocessingofcellulose.

II

III

Listofabbreviations,orderedbyappearanceinthetext

IαAtriclinicstructureIβ AmonoclinicsturctureNMMO N‐methylmorpholine‐N‐oxideNMR NuclearMagneticResonanceNON‐oxidegroupofN‐methylmorpholine‐N‐oxideDMAcDimethylacetamideDPDegreeofpolymerizationCF11CellulosepowderPFParaformaldehydeDMSODimethylsulfoxideTEACTriethylammoniumchlorideILsIonicliquidsTSILsTaskspecificionicliquidsAmimCl3‐Allyl‐1‐methyl‐imidazoliumchlorideEohmimCl1‐(2‐Hydroxylethyl)‐3‐methylimidazoliumchlorideEDAElectrondonoracceptormechanismβTheabilitytomakehydrogenbondBmimCl3‐Butyl‐1‐methyl‐imidazoliumchlorideDCMDichloromethaneC4mimCl1‐Butyl‐3‐methyl‐imidazoliumchlorideC6mimCl1‐Hexyl‐3‐methyl‐imidazoliumchlorideC8mimCl1‐Octyl‐3‐methyl‐imidazoliumchlorideC2mimOAc1‐Ethyl‐3‐methyl‐imidazoliumacetateC4mimOAc1‐Butyl‐3‐methyl‐imidazoliumacetateTMG1,1,3,3‐TetramethylguanidineMCCMicrocrystallinecelluloseTMGPr1,1,3,3‐TetramethylguanidinepropionateTMGOAc1,1,3,3‐TetramethylguanidineacetateTBAFTetrabutylammoniumfluorideBDMTDAClBenzyldimethyltetradecylammoniumchlorideTEMAMTriethylmethylammoniumTBMAMTributylmethylammoniumC4mpyCl3‐Methyl‐N‐butylpyridiniumchlorideBDTACBenzyldimethyltetradecylammoniumchlorideTFSABis(trifluoromethylsulfonyl)amideICIonchromatographym.p.Meltingpointt‐BuOKPotassiumtert‐butoxideDMFDimethylformamideNMBAN,N‐dimethylethanolamineNMPN‐methyl‐pyrrolidinone2‐Pyr2‐PyrrolidinoneTHFTetrahydrofuranDCMDichloromethaneBMMorpOAcN‐butyl‐N‐methyl‐morpholiniumacetateBMMorpBrN‐butyl‐N‐methyl‐morpholiniumbromide(ΔE)Energydifference

IV

AMMorpOAcN‐allyl‐N‐methyl‐morpholiniumacetateBnMMorpOAcN‐benzyl‐N‐methyl‐morpholiniumacetateBnMMorpClN‐benzyl‐N‐methyl‐morpholiniumchlorideAMMorpBrN‐allyl‐N‐methyl‐morpholiniumbromideAMMorpHSO4N‐allyl‐N‐methyl‐morpholiniumbisulfateAMMorpOHN‐allyl‐N‐methyl‐morpholiniumhydroxide[AMMorp]2CO3N‐allyl‐N‐methyl‐morpholiniumcarbonate[AMMorp]3PO4N‐allyl‐N‐methyl‐morpholiniumphosphateAMMorpH2PO4N‐allyl‐N‐methyl‐morpholiniumdihydrogenphosphate

V

TableofcontentsAbstract.................................................................................................................................................I 1. Introduction...................................................................................................................................1 1.1Structureofcellulose...............................................................................................................................1 1.2Dissolutionofcelluloseprocesses.....................................................................................................2 

1.2.1Viscoseprocess ........................................................................................................ 2 1.2.2NMMO(N‐methylmorpholine‐N‐oxide)process ................................................. 3 1.2.3LiCl/dimethylacetamide(DMAc)process ............................................................. 5 1.2.4Alkali/urea/thioureaprocess ............................................................................... 5 1.2.5IonicLiquids(ILs)process ..................................................................................... 6 

2. Experimentalmethods............................................................................................................11 2.1Ionchromatography.............................................................................................................................11 2.2Opticalmicroscopy................................................................................................................................11 2.3Nuclearmagneticresonancespectroscopy................................................................................12 2.4Karl‐Fischertitrationmethod..........................................................................................................13 3.Experimentalsection...............................................................................................................13 3.1Materials....................................................................................................................................................13 3.2Preparationofionicliquids...............................................................................................................14 

3.2.1PreparationofN‐butyl‐N‐methyl‐morpholiniumbromide[BMMorp][Br] ..... 14 3.2.2PreparationofN‐butyl‐N‐methyl‐morpholiniumacetate[BMMorp][OAc]........14 3.2.3PreparationofN‐allyl‐N‐methyl‐morpholiniumbromide[AMMorp][Br] ........ 15 3.2.4SynthesisofdifferentN‐allyl‐N‐methyl‐morpholiniumsalts ............................ 16 3.2.5PreparationofN‐benzyl‐N‐methyl‐morpholiniumchloride[BnMMorp][Cl] ... 17 3.2.6SynthesisofN‐benzyl‐N‐methyl‐morpholiniumacetate[BnMMorp][OAc] ..... 18 

3.3Regenerationofcellulose ............................................................................................... 18 3.4Recoveryofionicliquids ................................................................................................ 19 4.Resultsanddiscussion............................................................................................................19 4.1Synthesisofionicliquids........................................................................................................19 

4.1.1SynthesisofN‐butyl‐N‐methyl‐morpholiniumsalts....................................................19 4.1.1.1Effectofsolventontheyieldof[BMMorp][OAc] ............................................. 19 4.1.1.2IonExchangemethod ......................................................................................... 20 4.1.3SynthesisofN‐allyl‐N‐methyl‐morpholiniumsalts......................................................20 4.1.4SynthesisofN‐benzyl‐N‐methyl‐morpholiniumacetate...........................................21 4.1.5.Determinationoftheamountofwaterinionicliquids.............................................21 

4.2Dissolutionofcellulose........................................................................................................................22 4.2.1DissolutionofcelluloseinN‐butyl‐N‐methyl‐morpholiniumacetate‐brine .... 22 4.2.2Dissolutionofcelluloseinorganicelectrolyticsolutions ................................... 22 4.2.2.1Theinfluenceofamines .................................................................................... 23 4.2.2.2Effectofproticsolvents ..................................................................................... 23 4.2.3DissolutionofcelluloseinN‐allyl‐N‐methyl‐morpholiniumsalt‐brines .......... 24 4.2.4DissolutionofcelluloseinN‐benzyl‐N‐methyl‐morpholiniumacetate‐brine . 26 4.2.5Analysisofcellulosesolutionusingopticalmicroscopy .................................... 26 4.2.5.1Analysisofcellulosesolutionin[BMMorp][OAc]‐brine ................................. 26 4.2.5.2AnalysisofcellulosesolutionN‐allyl‐N‐methyl‐morpholiniumsalt‐brines .. 28 4.2.5.3Analysisofcellulosesolutionin[BnMMorp][OAc]‐brine ............................... 26 

4.3Regenerationofcellulose....................................................................................................................30 4.4Recoveryofionicliquids.....................................................................................................................30 5.Conclusions.................................................................................................................................31 6.Acknowledgement....................................................................................................................33 

VI

7.References...................................................................................................................................348.Appendixes.....................................................................................................................................1

1

1. Introduction

Withthemodernizationofthirdworldcountriesandincreasinginindustrializationallover theworld, theconsumptionof fossil resourcesarepeaking.Consequently it isestimated thatmeaningful resourcesof fossil oilwill beusedupafter50yearswhichwillresultinaglobalenergycrisisinnearfuture.Hence,worldcommunityimmediatelyneeds to find alternatives to replace fossil oil mainly from bio‐renewable andsustainablematerials.Biofuelscanprovideasustainablealternativetofossilfuels.Theproducts from cellulose have beenwidely used inmany industries viz. papermaking,construction industry, agriculture, plastic and electronics [1]. Cellulosic ethanolproducedfromnon‐foodsourcessuchastreesandgrass,canconstituteamajorpartofbiofuels [2].However, to exploit the fullestpotential of the cellulose, itsdissolution isextremelyimportant.Alargearrayofresearchhasbeendevotedforthedevelopmentofsuitablesystemforcellulosedissolutionasitwillleadtomoreandmoreusefulproductsfromcellulose.Infuture,cellulosewillplayanimportantroleforrenewablematerials.1.1Structureofcellulose

Cellulose is the richestbiopolymerand renewable resourceon theearth.Cellulosecan be obtained from byproduct of agricultural products, like cornhusk, rice straw,wheatstrawandsugarcanebagasseandalsocanbeobtainedfromanimalsandbacteriaaswellassomeamoebas[3].Mostoftheseresourcescontaincellulose.Asanexample,woodspeciestypicallycontain40‐50%ofcellulose,10‐30%hemicelluloseand20‐30%lignin.Themostcelluloserichspeciesiscottonwhichcontainsalmost100%cellulose[4].Celluloseconsistsofcrystallineandamorphousregions.Differentgrowthconditionslead to various micro‐fibril structures of native cellulose due to biosynthesis by theplants themselves. Nevertheless, the structure of cellulose comprises primarily twoanhydroglucoserings(C6H10O5)n,thenfrom100000to150000(wherenisdependenton the source of the rawmaterial) that are coupled with oxygen covalent bond, theoxygen linksC1ofoneglucosewithC4ofanotheranhydroglucosering[5].Additionallinksareintra‐chainandintermolecularhydrogenbondsbetweenhydroxygroupsandoxygenoftheadjoiningringoradjacentmolecules.Allthesemakethecellulosealinearstructure containing stacking ofmultiple cellulose chain. Thousands of these types ofstructurearerepeatedandformarigidandrelativelystrongernetwork;eithertheintra‐or inter‐chain hydrogen bonding network renders the cellulose a very stablebiopolymer.Therefore,a largeamountofanhydroglucoseringsarelinkedtogether.Socelluloseconsistingofa largenumberof linearly linkedβ(1→4) linkedD‐glucoseunits[6],thestructureofcelluloseisshownatFigure1.

oo o

o**

OH

OH

OH

OH

HO

HO

n

123

4 5

6

123

4 56

Figure1:Structureofcellulose[5]

2

Cellulose commonly is divided into four types polymorphs of crystalline cellulose(I,II,III,IV). Cellulose I has two different polymorphs which form native samples, atriclinicstructure(Iα)andamonoclinicstructure(Iβ).AlthoughtheIαandIβhavethesameatomskeleton,differenthydrogenbondingpatternsoccur.Theycanco‐existwithdifferentpercentproportionsincelluloseIaccordingtothevariouscellulosesources[7].TheIαgenerallydominantsinalgaeandbacteria,howevertherearemoreIβthanIαinseniorcellwallspeciesandIβdominatesinplantsandintunicates[8].Iαismeta‐stableandmore reactive than Iβ, and, therefore Iα can be convert to Iβ in alkaline solutionwhenusinghydrothermaltreatmentsat260°C(hightemperatures)insuitablesolventsunderheliumgas.IαpolymorphismorecommoninthealgaeandbacteriaandtheaimofmanyresearchersistocompletelyconvertIαtoIβwhichstillhasnotbeenachievedupuntilnow[9‐10].Nishiyamaandhisco‐workersfoundthatIαandIβhavedifferentlattice planes and different geometry and in the basis of these results it can bespeculatedthathydrogenbondingofIαisweakerthanthatofIβ.Thus,Iαcanthermallydegradeatlowertemperaturesandhasalowerstability[11‐12].

CelluloseIIcanbeobtainedfromcelluloseIwhensubjectedtoatreatmentwithionicliquidsandothersolventsupondissolutionofcelluloseI.Generallyspeaking,mostofthecellulose II is formed during the regeneration process by ionic liquids, also obtainedafter treatment with aqueous sodium hydroxide [13]. Cellulose II has a monoclinicstructureandarrangesinanti‐parallelsheets .Throughaqueousammoniatreatmentofcellulose I or II yet another cellulosepolymorph canbeobtained: cellulose III.WhoseintraandinterhydrogenbondsaresimilartocelluloseII,but,thechainsaresimilartocelluloseIwhichisparallel[14].

Celluloseisextremelydifficulttodeconstructusingcommontechnologiesduetothestiff bio‐molecules and long inter and intra hydrogen bond chains of cellulose. Thuscellulose is insoluble inwaterand theotherorganic solvents suchasethanol,acetoneand benzene; All previously mentioned properties of cellulose cause challenge upondissolutionofcellulosealthoughcellulosecanbedissolvedinseveralcomplexsolvents,suchasCu(NH3)4(OH)2, [NH2CH2CH2NH2]Cu(OH)2, [NH2CH2CH2NH2]Zn(OH)2, ([Pd(NH2

(CH2)2NH2)](OH)2and so on [15‐16]. If the desire is to dissolve cellulose, the mostimportant thing is to disrupt hydrogen bonding of cellulose and then get variousderivativesofcellulosefromdifferentprocesses.Asafurthertechnologydevelopment,several different processes for the treatment of cellulose exist. Currently, the mostimportant and dominant process used to produce cellulose fibers is the viscoseprocessingtechnology,calledthe“viscoseprocess”.

1.2Dissolutionofcelluloseprocesses

1.2.1Viscoseprocess

In1855,thefirst“artificialsilk”wasproducedbyGeorgesAudemars.Unfortunately,hisprocess ishardlycommercialized.First commercialviscoserayonwassuccessfullyproduced in 1905 and since then viscose rayon is dominating the global fibermarket[17].TheschematicdiagramofviscoseprocessisshownatFigure2.Pulpandsodiumhydroxide (NaOH) are added to the slurry tank, cellulose is steeped by sodiumhydroxideinsideslurrytankandthecelluloseisconvertedintoalkalicellulose.Mostofthepulpcanbedissolvedintheslurrytank,whereastheresidualhemicelluloseandlow

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molecularweightcelluloseareremovedbythefilterpress.Afterseveralprocessessuchaspressing,shredding,the“whitecrumb”wasformed.Thewhitecrumbshouldbestayat aging drum to be oxidized and depolymerized by contacting with air. Thedepolymerization can produce short chain lengths providingmanageable viscosity tothe spinning solution. Then the aged white crumb is transported to xanthator.Xanthation will occur upon addition of carbon disulphide (CS2) into xanthator. Thecarbon disulphide reacts with alkali cellulose to form cellulose xanthate. Inorganicimpuritiesarealsotobeformedduetoreactionofthecarbondisulfidewiththealkalinemediumwhichgivesyellowcolor to themixture.Theproduct fromwhite crumbnowchangedto“yellowcrumb”[18].

The yellow crumb is passed to the dissolved hopperwhereupon it is dissolved inaqueous caustic solution.However, the yellow crumb cannot bedissolved completely,becausethereareblocksofunxanthatedhydroxylgroupsinsideofcrystallineregionsofcelluloseand,asaresult,themixturebecomesveryviscous.Throughripening,filtrationandde‐aeration, thesolutionistransferredtospinningwhereit ismixedwithsulfuricacid(H2SO4)andotheradditives.Whenthesolutioncomesincontactwiththesulfuricacid, the xanthate groups are converted to unstable xantheic acid groupswhich loosecarbondisulphidetoformthefilamentsorrayonfibers[18].Duringtheprocesscarbondisulphideisreleasedandcanberecycled.

Althoughviscoseprocessiswidelyemployedinthefibersindustry,thistechnologyneedsalargeamountoffreshwaterandusesverycorrosivechemicalssuchassodiumhydroxide and sulfuric acid. Moreover, carbon disulphide can cause serious nervoussystemproblemsonhumanbeings[19].

Figure2:Processesdiagramofviscoseprocess

1.2.2NMMO(N‐methylmorpholine‐N‐oxide)process

The other fiber production technology industrialized in theworld is the so calledNMMO process. NMMO (Figure 3) is synthesized of a tertiary amine N‐methylmorpholinewith hydrogen peroxide (H2O2). NMMO as a solvent for dissolvingcellulosewascommercialized intheearly1990s. ItcandissolvecelluloseandproduceLyocell fibres.However, this technology causeshigh fibrillationof fibres [20].A lot ofstudies has been done for the improvement the fiber quality, viz, addition of some

4

surfactants as additives to the precipitation bath, adjusting pH during the washingprocessanddriedfibertreatedwithswellingmedia‐dimethylsulfoxide,ZnCl2,NMMOorcross‐linking agents (mono and bifunctional hydroxyl group containing compounds)[21].NMMOprocessisbasedonthewater‐NMMO‐cellulosesystem(3‐phasediagramofthecomponents).ThecellulosedissolutionstatedependsontheamountofNMMOandwater.Ithasbeenshownthatonlyanarrowregionworks:17%to23%water,60%to68%NMMO,whereuponupto23%cellulosecanbedissolved[22].

AlthoughNMMOprocesswasusedinindustryforafewdecades,thereisnotavery

clearmechanismfordissolutionofcelluloseandthestructureofcellulose–water–NMMOsolutions.However,Gagnaireetal.hadprovedthatthereisnotcellulosederivatizationin cellulose–water–NMMO solutions using nuclear magnetic resonance (NMR) [23].Otheracceptable interpretationisthatthereisastrongerdipolarN‐OgroupinNMMOand oxygen of N‐O group prefers to break hydrogen bonds for forming hydroxylatedcompounds.Thus, the cellulose canbedissolvedby theNMMOdue to the cleavageofinter‐orintra‐molecularhydrogenofcellulose.Nevertheless,uponpresenceofwaterinthe NMMO‐cellulose mixture, there is a competition between water and cellulose tocontactwith oxygen of NO groups, since hydrogen ofwater ismore hydrophilic thancellulosic OH hydrogen. Also,  the  oxygen of NO  group  is  likely  to prefer  the hydrogen of water,  resulting  in  cellulose being more  soluble  in  low  concentration of water  in 3‐phase diagram [24]. Further, the type of N‐O  in NMMO also  influences the solubility of cellulose. Roseneau et al. proved  that  there are  two different  types of N‐O  in NMMO molecules.  In solvents  with  negligible  solvent–solute  interaction,  about  95%  of  the  NMMO molecules showed a typical chair conformation with an axial N‐O while 5% had an equatorial N–O at room  temperature. Other  conformations,  such  as  boat  and  twist,  those  are  energetically largely  disfavored.  If  increasing  the  concentration  of  water  in  the  NMMO  solution,  the percentage of NMMO molecules with an axial N‐O was reduced from 95% to 75 %. On the other hand, the percentage of NMMO molecules with an equatorial N–O was  increased to 25 % from 5 %, the dissolution capacity of NMMO for dissolving cellulosewill be reduced [25].

NMMOprovidesasimplephysicaltechnologytoproducecellulosefibers,films,food

casings, membranes, sponges, beads and others without hazardous by‐products [26].However, the NMMO process gives rise to several side reactions which can causedeconstruct ofNMMO,modify the performance of product, consumemore stabilizers,andcausethermalrunawayreactionsoftheNMMOprocess[27].Thefibrillationtrendofcelluloseandthewholeprocessrequirescomplexsafetytechnologies.Thesefactorsstilllimitthefurtherexpansionoftheprocess[28].

O

N+

CH3 O-

Figure3:StructureofN‐methylmorpholine‐N‐oxide

5

1.2.3LiCl/dimethylacetamide(DMAc)process

BesidestheviscoseprocessandNMMOprocess,LiCl/DMAcasasolventtodissolvethenativecellulosehadbeenreportedbyTurbaketal.[29].Thecellulosewithadegreeof polymerization (DP) 100‐4000 can be dissolved in this solution. The influence oftemperatureandwaterinLiCl/DMAc/cellulosesystemwereevaluatedbyRamosetal.[30].Theresultsshowedthatahigherconcentrationofcellulosecanbedissolvedat5°Cthan at 25 °C under identical conditions which indicated that lower temperaturesimprove the dissolution of cellulose. As the temperature is relative with ion pairconcentrationofLiCl/DMAc,lowertemperaturesincreasetheionpairconcentration.Iftheconcentrationofwaterisincreasedinthesystem,higheramountofLiClisneededtodissolvesameamountofcellulose.

However, LiCl /DMAc system can dissolve cellulose without any additive at

temperatureshigherthan100°C.Whentemperatureisreducedto80°C,someadditivessuchasazeotropicmethanolorisopropanol[31‐32]andadipicanhydride[33]shouldbeadded,sincethereactionvelocitywillbeacceleratedbyaddingtheseadditives.Although,there are several differentmethods to dissolve cellulose used LiCl/DMAc, in a typicalsolventexchangeproceduretheprocessisasfollows:firstthecelluloseisimmersedintowater,thenexchangeofwaterbytheacetonetakesplace,further,byDMAc.Thissolventexchangeprocedure isgenerallycalledas ‘activation’ [34].Also,aseriesof thesolventsystems with a different proportion of LiCl/DMAc for cellulose powder (CF11),paraformaldehyde (PF)/ DMSO, triethylammonium chloride (TEAC)/DMSO have beenusedtofabricatecellulosehydrogelsdirectly[35].

Evidently, the mechanism of ‘activation’ is not very clear till now and several

presumptions have been made about how LiCl/DMAc systems dissolve cellulose.Chrapava etal. concluded that the intermolecular hydrogen bonds of cellulose can bebrokenbyLiCl/DMAcmixture.Moreover,oneanhydroglucoseunitneedstwoLiClunitsin the reaction resulting in two intermolecular hydrogen interactions. Otherwise thecellulose does not seem to be dissolved [34]. Ishii et al. investigated the molecularmobilityofcelluloseindifferentsolventswithLiCl[36],andtheyfoundthatmobilityofDMAc‐treated cellulose is faster than the others and theDMAc‐treated cellulose havelargesurfaceroughness.

1.2.4Alkali/urea/thioureaprocess

Ontheassumptionthatalkalicellulosecouldbeproducedandmaybedissolvedinother solvents except carbon disulphide, alkali/urea/thiourea process was invented.Generally,thealkaliissodiumhydroxide.Itisreportedthatcellulosecanbedissolvedinasolutionof9.5wt%NaOH/4.5wt%aqueousureaatlowtemperatures[37].Ithasbeendemonstrated that the intramolecularhydrogenbondsof celluloseweredestroyedbythe alkali/urea solution, as aqueous alkali solution can disrupt the chain packing oforiginalcelluloseandreformnewhydrogenbonds,whileureacanreduceaggregationofcellulose molecules [38]. Many studies demonstrated that when decreasing thetemperature, the solvent dissolution capability of different aqueous alkali/thioureasystemswasincreasedstrongly[39].Thismeansthatlowertemperaturesrepresentanadvantageintermsofcellulosedissolution.IfNaOHcomplexsolventwaspre‐cooledto–10°C,thehighestsolubilityforcellulosewasattained[40].

6

Zhangetal. foundout theoptimal ratiosofNaOH/urea/H2OandNaOH/ thiourea/H2Osolventscompositiontodissolvecellulose,correspondingto6:4:90and9.5:4.5:86,respectively[41].However,Qietal.discoveredanothermethodusingatwostepprocesstodissolvethecelluloseat‐5°C.Aftertheinitialtreatmentofcellulosewith12%‐18%NaOHabout4%‐6%thioureawasaddedtoaffordaclearsolution[38].Despitethefactthat these solvents systempossess a higher solubility capacity for cellulose andwererather inexpensive and less toxic, otherproblems remain:High alkalinity and the factthatthesolventcannotberecycledthusleadingtoseriousenvironmentalproblems.

1.2.5IonicLiquids(ILs)process

Anothertypeofsolventsystemusedtodissolvethecelluloseisrepresentedbyionicliquids(ILs).(Room‐temperature)Ionicliquidsarecommonlydefinedasfusedsaltsorionicsaltscomprisedofcationsandanions,andhavingmeltingpointsbelow100°C.ILshaveattractedhugeamountofresearchattentionduetotheirspecificphysicochemicalproperties,viz.,lowmeltingpoint,highthermalstability,lowflammabilityandnegligiblevaporpressure [42].When ionic liquidswhich incorporate functionalgroupsdesignedto impart to them particular properties or reactivities, it is called task‐specific ionicliquids(TSILS)[43].ILsareusedinvariouschemical fields,suchascatalysis,synthesis,separation,analysis,andenergysupply[44].ILscanoftenbedissolvedinpolarsolventssuchasacetone,dichloromethane(DCM)andmethanol.ThisrenderstherecyclingofILsplausible after the reaction. They can also offer advantages like atom economy ofprocess, safety and higher efficiency than conventional volatile organic solvents andimportantlyenvironmentalcompatibility[45].AsexamplesofcommonILs,imidazoliumandpyridiniumderivativesareconsideredasamongmostcommon.Ontheotherhand,e.g. the derivatives from phosphonium, tetraalkylammonium and guanidine have alsobeenusedforsomespecialpurposes,suchasmedicine,electrolyteandanalysis[46,47,48,49].

Figure4:Typicalcationsandanionsusedinionicliquids[50]

Figure4illustratestypicalcationsandanionsusedinionicliquids,thesubstitutesof

R1could any alkyl and alkenyl group. Different anions in combination with the samecation can generate different ILs with different physical and chemical properties.Tsunashimaetal.reportedthattheunsaturatedphosphoniumionicliquidshavelowermelting point, high thermal stability, lower viscous and higher conductive than thesaturatedphosphoniumionicliquids[51].

In1934,Graenacheretal.pointedout that1‐ethylpyridiniumchloridecandissolve

cellulose[52].Swatloskietal.studiedthedissolutionofcelluloseinimidazoliumbased

7

ionic liquids. They used the 3‐butyl‐1‐methyl‐imidazolium cation, combined with Cl−,PF6−, Br−, SCN‐, and BF4‐ anions. The results showed that only the Cl−, SCN− and Br−anionscontainingionicliquidshavetheabilitytodissolvecelluloseat100–110°C.Theyalso proved that microwave heating is more effective than conventional heating indissolutionofcelluloseintheseionicliquids[53].In2005,anovelionicliquid3‐allyl‐1‐methyl‐imidazolium chloride [Amim][Cl] was synthesized by Zhang etal.. This novelionicliquidcandissolvecellulosewithoutanypretreatments[54].Luoetal.synthesizedanewionic liquid1‐(2‐hydroxylethyl)‐3‐methylimidazoliumchloride[Eohmim][Cl] thuscombining –OH groups to the imidazolium cation and found that this ionic liquidperformsbetterinthedissolutionofcellulose(6.8wt%at70°C)[55].

Whydotheseionicliquidsdissolvecellulose?Accordingtoelectron‐donor‐acceptor

(EDA)mechanism,imidazoliumcationisanelectronacceptorandchlorideanionasanelectrondonor. Thus, the ionic liquid could interactwith oxygen andhydrogenofOHbodingofcellulose.Forthe[Eohmim][Cl]ionicliquid,OHgroupalsointeractswiththehydrogen bonding of cellulose, thus increasing the capacity of ionic liquid to dissolvecellulose.Theamorphousregionofcellulosewasinitiallydissolved,followedbyreactionof ionic liquid with the crystalline part of cellulose. Ionic liquid molecules thenpenetrated thecapillariesand intersticesof thecellulosestructureandcaused furtherbreaking of H‐bonding leading to dissolution of cellulose [56]. Fukaya etal. made aseriesof1,3‐dialkyl‐imidazoliumformateionicliquids[57].Theseionicliquidshadalowviscosity, polarity andwere free of halogen. All these ionic liquids had a potential todissolve cellulose due to their low viscosity and high hydrogen bond basicityβ(0.99)(the ability to make hydrogen bond) when compare with the chloride anions ionicliquids,suchas3‐allyl‐1‐methyl‐imidazoliumchloride[Amim][Cl](β0.83)and3‐butyl‐1‐methyl‐imidazoliumchloride(β0.84)[Bmim][Cl].

As, the structure of cellulose is composed of inter and intra molecular hydrogen

bonds, the higher hydrogen basicity of ionic liquids can weaken inter and intramolecularhydrogenbondsofthecellulose,causingthedissolutionofcellulose[57].Theregenerated celluloseproducts canbeobtainedbyaddinganti‐solvent, suchaswater,ethanol and acetone into the solution. The mechanism of regeneration involves theaddition of an anti‐solvent, such as water to the dissolution solution, thus extractingionic liquids into the aqueous phase. Thewatermolecules form hydrodynamic shellsaround the ionic liquidmolecules inhibiting the direct interactions between celluloseand ionic liquid molecules. Further, the ionic liquids can be recovered by vacuumevaporation [58]. Depending of the requirements for the final product, differentregenerationprocessesaredesignedleadingtodifferentformssuchasfilms,beads,gels[59].

1.2.5.1Imidazoliumbasedionicliquids

Ithasbeenfoundthatthatimidazoliumbasedionicliquidsdisplayahighefficiencyfor dissolution of cellulose. Swatloski etal. studied ionic liquids which containing 1‐butyl‐3‐methylimidazolium cations [C4mim]+ combined with a range of anions, fromsmall hydrogeN‐bond acceptors Cl‐ to large non coordinating anions [PF6]‐, alsoincluding Br‐, SCN‐, and [BF4]‐. They found that the cellulose was dissolved withoutpretreatment in these ionic liquids. Table 1 summarizes the dissolution of celluloseundervariousparametersindifferentimidazoliumbasedionicliquids[53].

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Table1:Dissolutionofcelluloseindifferentimidazolium‐basedionicliquids[53]

Ionicliquid Method

AmountofCellulose(wt%)dissolved

[C4mim][Cl]Conventionalheat(100°C)

(70°C)10%3%

[C4mim][Cl]Conventionalheat(80°C)

andsonication

5%

[C8mim][Cl] Conventionalheat(100°C) slightlysoluble

[C4mim][Br] Microwave 6%

[C4mim][SCN] Microwave 6%

[C4mim][BF4] Microwave insoluble

[C4mim][BF6] Microwave insoluble

[C6mim][Cl] Conventionalheat(100°C) 5%

Because [C4mim][Cl] possesses the ability to dissolve higher concentration of

cellulosequickerthantraditionalsolvents,theyspeculatedthat[C4mim][Cl]isahighlyeffective in breaking the extensive hydrogen bonding in cellulose due to presence ofchlorideions.However,thelargeralkylchainsattachedtoimidazoliumionicliquidslike[C6mim][Cl] and [C8mim]Cl are less efficient in dissolving cellulose. Erdmenger etal.studied the effect of alkyl chain length on 3‐alkyl‐1‐methyl‐imidazolium cationcombinedwithchlorideanionondissolutionofcelluloseandpointedoutthatthereisnoregular regulation for the solubility of 3‐alkyl‐1‐methyl‐imidazolium chloridewith itsalkyl chain length[59]. Alkyl chainwith less than six carbon units and odd‐numberedalkylchain length ismoreefficient in thedissolutionofcellulose thanevennumberofalkyl chain length,but theC4 chain lengthhas thehighest solubility for cellulose [60].Recently, 1‐butyl‐ 3‐methylimidazolium acetate [C4mim][OAc] ionic liquid illustratedbetter dissolution capacity of cellulose. Wu et al. have demonstrated that dissolvedpowerof1‐butyl‐3‐methylimidazoliumacetate[C4mim][OAc]forchitinismoreefficientthan[Amim][Cl]or[C4mim][Cl].ItisreportedthattheBASFcompanybeingoneofthepioneersinindustrialusageofILs,hasturnedto[C2mim][OAc]todissolvecelluloseonanindustrialscalebecauseofitsbetterphysicochemicalproperties,suchaslowtoxicity,lowercorrosivenessaswellaslowermeltingpointandviscosity.Also,importantly,thefavorablebiodegradabilityprofileshouldbeemphasized[61].

Sunetal. tested thesolubilityof [C2mim][OAc] insoftwood(southernyellowpine)

andhardwood(redoak)aftermildgrinding[62]. Itwasfoundthat[C2mim][OAc] isabetter solvent than [C4mim][Cl] for the dissolution of these wood samples, but hardwood is easier and faster to be dissolved than soft wood. The factors affecting ofdissolutionofwoodweretheparticlesizeofwood(powdermesh),pretreatmentwithmicrowaveandultrasound.Theyalsoshowedthataftercompletedissolutionofwoodin[C2mim][OAc], proper reconstitution using acetone/water (1:1 v/v) solvents affordedthecarbohydratefreeligninandcelluloserichmaterials.

9

1.2.5.2Guanidinebasedionicliquids

King et al. developed a new generation of ionic liquids derived from 1,1,3,3,‐tetramethylguanidine(TMG)whichobtainedbytreatingTMGwithaseriesofcarboxylicacids, such as formic, acetic and propionic acids. They successfully prepared 9 ionicliquidswith various acids. All of these ILs are studied for their dissolved capacity formicrocrystalline cellulose (MCC). They found that 1,1,3,3,‐tetraemethylguanidinepropionate, 1,1,3,3,‐tetraemethyl‐guanidine acetate and 1,1,3,3,‐tetraemethylguanidineformateshowedthegooddissolutionforthe5wt%ofMCCat100°Cwithin18h[63].

1.2.5.3Ammoniumionicliquids

Several solvent systems containing ammonium salts, such as DMSO/ tetrabutylammonium fluoride (TBAF) [64], benzyldimethyl (tetradecyl) ammonium chloridedihydrate(BDMTDACl.2H2O)[65]andtrimethylbenzylammoniumhydroxide(TritonB)[65]weredeveloped for thedissolutionof cellulose.Kohleretal. prepareda seriesoftriethylmethylammonium (TEMAM) and tributylmethylammoniium (TBMAM) basedionic liquids as shown inTable2. Among those, TEMAM formate ([CH3N(CH2CH3)3]‐[HCOO]) and TBMAM formate ([CH3N(CH2CH2CH2CH3)3][HCOO]) could dissolvecellulose. Itwasalsoshownthatanadditionasmallamountsof formicacidhelpedtoreducethemeltingpointandincreasedthedissolutionvelocityofcellulose[67].Table2:PhysicalpropertiesofTEMAMandTBMAM‐basedionicliquids

No. Cation Anion Color Melting point ( °C)

1 TEMAM HCOO colorless 155

2 TEMAM ClCH2COO white 130

3 TEMAM Cl2CHCOO white 40

4 TEMAM Cl3CCOO white 47

5 TBMAM HCOO yellow <20

6 TBMAM ClCH2COO white 55

7 TBMAM Cl2CHCOO colorless <20

8 TBMAM Cl3CCOO yellow <20

The solubility of cellulose with a DP in the range from 290 to 1200 was studied

among3‐methyl‐N‐butylpyridiniumchloride[C4mpy][Cl], BDMTDACland1‐N‐butyl‐3‐methylimidazolium chloride [C4mim][Cl]. They found that the amount of dissolvedcellulose decreased with increasing DP of the sample. Different ILs have differentamounts dissolution of cellulose, the ionic liquid [C4mpy][Cl] is more effective than[C4mim][Cl] in terms of dissolution of cellulose. BDMTDACl could dissolve the lowestamount of cellulose (5wt%), but it has the advantageof the lowestmeltingpoint of

10

52°C[68].

1.2.5.4Phosphoniumbasedionicliquids

Phosphonium ionic liquids have several advantages than imidazolium andammonium ionic liquids in terms of thermal and chemical stability. Tsunashima etal.have demonstrated a series of phosphonium ionic liquids based on triethylbutyl‐phosphonium (P2224+), triethylpentyl‐phosphonium (P2225+), triethyl (methoxy‐methyl)phosphonium (P222(101)+) and triethyl(2‐ethoxy‐methyl) phosphonium(P222(201)+) cations combining with trifluoromethylsulfonyl amide (FSA) anion. Allthese ionic liquids have lowmeltingpoints compared to imidazoliumand ammoniumionic liquids. When combined with bis(trifluoromethylsulfonyl) amide(TFSA) anion,these ionic liquids show lower viscosities and higher conductivities than thosecombinedwithFSAanion[69].Introductionofmethoxygroupinphosphoniumcationsimprovetransportpropertiesoftheionicliquidsbecausethemethoxygroupcandonatean electron which reduces the positive charge of cation [70]. The unsaturatedphosphonium ionic liquids have lower melting points, lower viscosity, high thermalstabilityandhigherconductivitythanthesaturatedphosphoniumionicliquids[51].

Abe et al. reported that tetrabutylphosphonium hydroxides containing a certain

amountwaterwhichdissolvedcellulose[71].Theypointedoutthe30‐50wt%waterinthisionicliquiddissolved15wt%celluloserapidlyatroomtemperatureandsuggestedthe hydroxide anions of ionic liquid interacted with protons of hydroxyl group ofcellulose.

1.2.5.5Pyridiniumbasedonionicliquids

Early1934,Granenacherappliedforpatentforcellulosesolutionwhichpointedoutthatbenzylpyridiniumchloridehasacapacitytodissolvethecellulose[52].Though3‐methyl‐N‐butylpyridinium chloride [C4mpy][Cl] can dissolve a higher percent ofcellulose (approximately 38wt%), [C4mpy][Cl] and the reagents degraded during thereactionwith cellulose, so this ionic liquiddoes not render a successful candidate forcelluloseprocessing[68].

1.2.5.6Influenceofwaterinionicliquidoncellulosedissolution

Almost all reports on dissolution of cellulose in ionic liquids clearly indicated thenegative influence of water on dissolution of cellulose in ionic liquids [52‐63]. It isconsideredthatmorethan0.5molefractionofwaterinionicliquidsignificantlyreducedthe solvent properties of ionic liquid and resulted in a system that couldnot dissolvecellulose [58]. Thismainly happens due to possible competition between ionic liquidandwaterforaccessibleactivefunctionalgroupsofthecellulose.Thestronginteractionofcellulosichydroxylgroupwithwatermolecule inhibit the interactionof ionic liquidwithcelluloseandresultinnon‐dissolutionofcelluloseinionicliquid.

Thewater is found tobeoneof themajor impurities in ionic liquids, especially in

hydrophilicionicliquids.Innormalbench‐toplaboratoryconditions,oneshouldexpecthighcontentofwaterthanthosepreparedingloveboxandwiththeuseofhighvacuum

11

pumps. Also, water can be readily absorbed in ionic liquid from atmosphere duringstorage or experiments. Most of these reports insist the dryness of ionic liquid foroptimumdissolutionofcellulose.However,thesestringentrequirementsofdrynesscancreategreatdifficultyintermsofcostintheirapplicationinindustrialscale.Thus,itishighly importanttodevelopnewionic liquidswhichcandissolvecelluloseevenunderhighwatercontentconditions.

2. Experimentalmethods

In this work, several analytical technologies were used, viz. Karl Fischer titrationmethod, ion chromatography(IC), rotary evaporation system, optical microscopy andnuclearmagneticresonance (NMR)spectroscopy.Abrief introductionofthesesystemsisdescribedasbelow.

2.1Ionchromatography

Ionchromatography(IC)isarapidanalyticalmethodusedforquantitativeanalysisofaqueoussamplesinparts‐per‐million(ppm)orevenless.Manyionscanbeanalyzedquantitatively (such as chloride, bromine, and common cations like sodium andpotassium) using conductivity detectors of IC. IC represents one kind of liquidchromatography that contains different ion‐exchange resins in column to separateatomic or molecular ions based on their interaction with the resin. The mixture ofNa2CO3 or NaHCO3 is commonly used as the mobile phase, upon which the eluentsuppressorsuppliesH+toneutralizetheanionandretainorremoveNa+[72].Most ICequipmentscontainapump,injector,filter,columnelectrolyticsuppressoranddetector,asshowninFigure.6.Fortheaniondetermination, thecolumnusedinthisstudywasANX‐99‐8511, IC Sep AN1, Peek 4.6mm 250mm. The active length of the anionsuppressorcolumnwas100mmlong.

Figure5:Theoperationalprincipleofanionchromatography

2.2Opticalmicroscopy

Microscopy is a technology for magnification of small specimen which cannot beseen with naked eye. The principle of microscopy is using multiple‐lens (compoundmicroscopes)throughdiffractionandreflectiontogetamagnifiedvisual image.Asthe

12

developmentof technology, themodernopticalmicroscopyoftenhasaccessoriessuchaswithacamera,computer,high‐end fluorescencedetectorandso forth.Theefficientillumination and all these add‐onsmake themicroscopymore efficient, provide highresolution and high‐quality images about the specimen [73]. An optical microscopy(AXIOSKOP40)wasusedtoinvestigatethedissolutionofcellulose.

Figure6:Aphotographofopticalmicroscope

2.3Nuclearmagneticresonancespectroscopy

Nuclearmagnetic resonance (NMR) spectroscopy is an important characterizationtool toverify thestructureandqualityofchemicals.NMRspectroscopybeingusedfordeterminingthecontentofsampleandstructuresofanatomormolecules,duetotheirmagnetic nuclei in amagnetic field can absorb and re‐emit electromagnetic radiationundertheapplicationofanappliedmagneticfield.NMRspectroscopyalsocanprovidedetailedstateandchemicalshiftofmoleculeswhichhelpscientiststoconfirmphysicaland chemical properties of their products. In our case, proton nuclear magneticresonance spectroscopy was used for determination of proton skeleton of products.Normally,protonsarespinninginrandomlyorientation.Onceanexternalmagneticfieldisapplied,protonswillspineitherparallelorantiparallel it, theprotonswithparallelspinhaslowerenergythanonewithantiparallelspin.Hence,anenergydifference(ΔE)between the parallel and anti parallel states will be created. The signal in NMRspectroscopyresultsfromthedifferenceandisproportionaltothepopulationdifferencebetweenthestates[74].

13

Figure7:Aphotographofnuclearmagneticresonancespectrometer

2.4Karl‐Fischertitrationmethod

KarlFischertitrationisananalyticalmethodwhichdesignedtodeterminethewatercontent inavarietyofproducts.Theprinciple isbasedon thequantitativereactionofwater with iodine and sulfur dioxide, which used a primary alcohol (methanol) assolventandanorganicbase(pyridine)asbufferingagent.Thereactionwasdescribedasbelow.I2‐Pyr+SO2‐Pyr+Pyr+H2OSO3‐Pyr+2PyrH+I‐SO3‐Pyr+CH3OHPyrH+CH3SO4WherePyrrepresentspyridine.Theproduct,SO3‐Pyrreactsfurtherwiththemethanoltoformthemethylsulfateanion.TherearetwodifferenttechniquesfordeterminationofwatercontenttoKarlFischer:Volumetric and Coulometric titration. Volumetric Karl Fischer Titration, where asolutioncontainingiodineisaddedusingamotorizedpistonburetteandwhereiodineisgenerated by electrochemical oxidation in the cell. The selection of the appropriatetechniqueisbasedontheestimatedwatercontentinthesample[75].3.Experimentalsection

3.1Materials

Most of the chemicalswere purchased from Sigma Aldrich Ltd., such asN‐methylmorpholine,N,N‐dimethylethanolamine (DMEA), dimethylformamide (DMF),N‐methylpyrrolidinone(NMP),N,N‐dimethylbenzylamine,2‐pyrrolidinone,N,N,N',N'‐tetramethylguanidine(TMG), allyl bromide, benzyl chloride, 1‐bromobutane. Amines and alkylhalides were redistilled before further use. Acetic acid (100%), formic acid (100%),sodium acetate (≥99.0%), potassium acetate (≥99.0%), potassium tert‐butoxide(≥98.0%), potassium carbonate (≥99.5%), potassium phosphatemonobasic (≥99.0%),potassium phosphate tribasic (≥98.0%) sodium bisulfate (≥95.0%) and sodium

14

hydroxide (≥99.8%) were purchased from Merck. Ethanol (≥99.5%) and n‐butanol(100%)were purchased from Solveco Ltd. Amberlite IR‐400OH resinwas purchasedfromSigmaAldrichLtd.CellulosewasobtainedfromAdityaBirlaDomsjöAB(dissolving,sulfitecellulose).

3.2Preparationofionicliquids

3.2.1PreparationofN‐butyl‐N‐methyl‐morpholiniumbromide[BMMorp][Br]

In 250mL threeneck roundbottom flask, redistilledN‐methylmorpholine (1 eqv)and 1‐bromobutane (1.5 eqv) were added to acetonitrile (10 vol). The solution wasstirred at 70 0C for 24 h under nitrogen atmosphere (Scheme1). The flaskwas thenbrought to room temperature andplaced in a freezer at 4 0C for 12h.White crystalswereslowlyformingwhichwerefilteredandrecrystallizedwithtetrahydrofuran(THF)andisopropanol.Theresultingwhitesolidwasdriedandstoredindesiccator.M.P.:2080C1HNMR:(400MHz,CDCl3):δ(ppm)=0.98(t,3H),1.46(m,2H),1.78(m,2H),3.62(s,3H),3.67(m,2H),3.86(m,4H),4.09(m,4H)

o

N Br

Acetonitrile

70 oC 24 h

o

N

Br -

+

N-methylmorpholine N-butyl-N-methyl- morpholinium bromide[BMMorp][Br]

Scheme1:PreparationofN‐butyl‐N‐methyl‐morpholiniumbromide

3.2.2PreparationofN‐butyl‐N‐methyl‐morpholiniumacetate[BMMorp][OAc]

3.2.2.1Usingsodiumacetate

[BMMorp][Br](1.0eqv)andsodiumacetate(1.5eqv)wereputintoround‐bottomflaskindifferentsolvents(dichloromethane,methanol,ethanol,water,n‐butanol)andstirredvigorouslyatroomtemperaturefor24h(Scheme2).Thesolidwasfilteredthroughfunnel,solventisremovedundervacuum.Aviscouscolorlessliquidslowlychangedtoasemi‐viscousliquid.

o

N

Br -

+

N-butyl-N-methyl-morpholinium bromide

NaOAc

Solvent,R.T.

o

N

OAc -

+

N-butyl-N-methyl-morpholinium acetate

[BMMorp][OAc][BMMorp][Br]

Scheme2:PreparationofN‐butyl‐N‐methyl‐morpholiniumacetate

3.2.2.2Two‐stepapproach

15

[BMMorp][Br](1eqv)andpotassiumtert‐butoxide(1.5eqv)wereaddedtogetherinethanol(10vol)inconicalflask.Thesolutionwasstirredfor24hatroomtemperature(Scheme3).Thesolidobtainedwasfilteredandwashedseveraltimeswithethanol.Toethanolicsolution,aceticacid(1.5eqv)wasaddedandsolutionwasstirredvigorouslyfor 24 h. The ethanol was then removed on a rotary evaporation. The product wasdissolved in dichloromethane and filtered to remove undissolved potassiumbromide.Evaporationofdichloromethaneresultedinasemi‐viscousfluid.

o

N

Br -

+

[BMMorp][Br]

KOtBu

Ethanol

o

N

CH3OtBu -

+

o

N

OAc-

+

N-butyl-N-methyl- morpholinium acetate

Acetic acid

R.T.

[BMMorp][OAc]

Scheme3:TwostepapproachforpreparationofN‐butyl‐N‐methyl‐morpholiniumacetate

3.2.2.3IonExchangemethod

10.0gAmberlite IRA‐400(R‐OH) indeionizedwaterwas loaded inaglass column.100mLsolutionof1.0MKOAcsolutionwasthenpassedthroughthecolumnwithflowratearound1mL/min.ThecolumnwasthenthoroughlywashedwithdeionizedwatertillthepHoftheeluentwassameasthatofdeionizedwater.

[BMMorp][Br] (3.5 0g, 0.296 M) was dissolved in 50 mL deionized water. The

solutionwasloadedtothecolumncarefully.Thecolumnwasthenelutedwithdeionizedwater as an eluentwith a controlled flow rate of 1mL/min. Around 10mL of eluentsolution was collected in each test tube and analyzed by ion chromatography. Thesolution in test tubes containing pure [BMMorp][OAc]was evaporated under vacuumanddriedtoobtaincolourlessliquid.1HNMR:(400MHz,CDCl3):δ(ppm)=0.98(t,3H),1.44(m,2H),1.74(m,2H),1.89(s,3H),3.56(s,3H),3.73(m,2H),3.83(m,4H),4.02(m,4H)

3.2.3PreparationofN‐allyl‐N‐methyl‐morpholiniumbromide[AMMorp][Br]

In250mLroundbottomflask,N‐methylmorpholine(1eqv)andallylbromide(1.5eqv) were added to acetonitrile (10 vol). The solution was stirred at 70 0C for 24 h(Scheme4).Theflaskwasthenbroughttoroomtemperatureandplacedinafreezerat

16

4 0C for 12 h. Pale white crystals were slowly forming which were filtered andrecrystallizedwithtetrahydrofuranandisopropanol.Theresultingpalewhitesolidwasdriedandstoredindesiccator.M.P.:1820C.

1HNMR:(400MHz,CDCl3):δ(ppm)=3.56(s,3H),3.77(m,4H),4.05(m,4H),4.68(d,2H),5.79(d,1H),5.91(d,1H),6.02(m,1H)

o

N Br

Acetonitrile

70 oC 24 h

o

N

Br -

+

N-allyl-N-methyl-morpholinium bromide[AMMorp][Br]

N-methylmorpholine

Scheme4:PreparationofN‐allyl‐N‐methyl‐morpholiniumbromide

3.2.4SynthesisofdifferentN‐allyl‐N‐methyl‐morpholiniumsalts

Step I: [AMMorp][Br] (1.0 eqv) was dissolved in ethanol and a small amount ofdeionized water which then treated with 1.5 eqv of metal salts (sodium acetate,potassium carbonate, potassium phosphate tribasic, potassium phosphatemonobasic,sodiumbisulfateandsodiumhydroxide),stirredvigorouslyatroomtemperaturefor24h(Scheme5),inordertoobtaincorrespondingN‐allyl‐N‐methyl‐morpholiniumacetate[AMMorp][OAc],N‐allyl‐N‐methyl‐morpholiniumcarbonate [AMMorp]2[CO3],N‐allyl‐N‐methyl‐morpholinium phosphate [AMMorp]3[PO4] N‐allyl‐N‐methyl‐morpholiniumdihydrogen phosphate [AMMorp][H2PO4], N‐allyl‐N‐methyl‐morpholinium bisulfate[AMMorp][HSO4],N‐allyl‐N‐methylmorpholiniumhydroxide[AMMorp][OH]respectively.Thesolidwasfilteredthroughfunnelandsolventwasremovedundervacuum.Differentviscousyellow liquidswereobtained.These liquidswere furtherpurified through ionexchangemethod.

17

NaX

Ethanol,R.T.

o

N

Br -

+

N-allyl-N-methyl-morpholinium bromide

[AMMorp][Br]

o

N+

N-allyl-N-methyl-morpholinium salt

Ion exchange

KXor

Xn-

n

[AMMorp]n[X]n-

o

N+

N-allyl-N-methyl-morpholinium salt

Xn-

n

[AMMorp]n[X]n-

Xn-=OAc-

CO32-

PO43-

H2PO4-

HSO4-

OH-

Scheme5:PreparationofN‐allyl‐N‐methyl‐morpholiniumsalts

Step II: 10.0 gAmberlite IRA‐400(R‐OH) indeionizedwaterwas loaded in a glasscolumn.100mLsolutionof1.0Mmetalsaltspassedthroughthecolumnwithflowratearound1mL/min.ThecolumnwasthenthoroughlywashedwithdeionizedwatertillthepHoftheeluentwassameasthatofdeionizedwater.

TheyellowliquidobtainedfromstepIwasdissolvedin50mLdeionizedwater.The

solutionwasloadedtothecolumncarefully.Thecolumnwasthenelutedwithdeionizedwater as an eluent with a controlled flow rate of 1 mL/min. Approximately 6 mL ofeluent solution was collected in each test tube and further analyzed by ionchromatographyorNMR.Thesolutionintesttubescontainingpure[AMMorp]n[X]n‐wasevaporatedundervacuumanddriedtoobtainyellowliquid.

N‐allyl‐N‐methyl‐morpholiniumacetate1HNMR:(400MHz,CDCl3):δ(ppm)=1.93(s,3H),3.43(s,3H),3.69(m,4H),4.01(m,4H),4.54(d,2H),5.74(d,1H),5.83(d,1H),5.98(m,1H)

3.2.5PreparationofN‐benzyl‐N‐methyl‐morpholiniumchloride[BnMMorp][Cl]In250mLroundbottomflask,N‐methylmorpholine(1eqv)andbenzylchloride(1.5

eqv) were added to acetonitrile (10 vol). The solution was stirred at 70 0C for 24 h(Scheme6).Theflaskwasthenbroughttoroomtemperatureandplacedinafreezerat4 0C for12h.Thewhitecrystalswere filteredandrecrystallizedwith tetrahydrofuranandisopropanol.Theresultingwhitesolidwasdriedandstoredindesiccator.m.p.:2530C.1HNMR:(400MHz,CDCl3):δ(ppm)=3.54(s,3H),3.76(m,4H),4.01(m,4H),5.32(s,2H),7.47(m,3H),7.68(m,2H)

18

o

N

Acetonitrile

70 oC 24 h

o

N

Cl -

+

N-benzyl-N-methyl- morpholinium chloride[BnMMorp][Cl

N-methylmorpholine

Cl

]

Scheme6:PreparationofN‐benzyl‐N‐methyl‐morpholiniumchloride

3.2.6SynthesisofN‐benzyl‐N‐methyl‐morpholiniumacetate[BnMMorp][OAc][BnMMorp][OAc]wassynthesizedinthreesteps.Inthefirststep,sodiumhydroxide

wasaddedto[BnMMorp][Cl]inmethanolandthesolutionwasstirredatroomtempera‐turefor1h.Whiteprecipitatesodiumchloridewasremovedbyfiltration.Inthesecondstep, acetic acid was added to the filtrate. The solution was stirred again at roomtemperaturefor1h.Afterevaporationofmethanol,theproductwasdissolveinacetoneandremaininginorganicsaltwasremoved.Finallytheproductwasfurtherpurifiedbythe ion exchangemethod. The product was dried under vacuum at 80℃ for 3h. Theproductwasanalyzedbyionchromatographyand1HNMR.1HNMR:(400MHz,CDCl3):δ(ppm)=1.98(s,3H),3.44(s,3H),3.71(m,4H),3.99(m,4H),5.15(s,2H),7.44(m,3H),7.61(m,2H).

o

N

Cl -

+

N-benzyl-N-methyl- morpholinium chloride[BnMMorp][Cl]

Methanol

NaOH

R.T.

o

N

HO-

+

N-benzyl-N-methyl-morpholinium hydroxide[BnMMorp][OH]

Acetic acid

Ion exchange

o

N

OAc-

+

N-benzyl-N-methyl-morpholinium acetate[BnMMorp][OAc]

Scheme7:PreparationofN‐benzyl‐N‐methyl‐morpholiniumacetate

3.3Regenerationofcellulose

Afterdissolutioncellulose,smallamountofthemixturewasputintotheglassslideandpressedthemixturewithcoverslip,makingathinfilm.Aftercoolingthefilmwhich

19

waswashedseveraltimeswithdistilledwater,thenthefilmwasdriedunder80℃for10min.Finallyawhitedryfilmwasobtained.

3.4Recoveryofionicliquids

Thecompletelydissolvedcellulosewasdilutedwith5‐foldamountofmethanolandkeptfor1h.Whenthecolorofcellulosewaschangedtowhite,theregeneratedcellulosewas separated with solution by filtration. The cellulose was isolated as hard beads(Figure 16a). The methanol was evaporated under vacuum for 3 h, getting aconcentratedliquidwhichwasanalyzedby1HNMRandusedtodissolvecelluloseagain.

4.Resultsanddiscussion

Variousionicliquids,mainlyimidazoliumcationbasedionicliquidshavebeenusedfor thedissolutionofcellulose.However, inspiteofmomentousefforts,onlya fewILscould efficiently dissolve cellulose. Although the so called NMMO process wassuccessfully industrialized for the dissolution of cellulose, very few reports exist thatdescribethedissolutionofcelluloseinmorpholiniumcationbasedionicliquids.Thus,itwas interesting to study the effect ofmorpholinium cation based ionic liquids on thedissolutionofcellulose,followedbyregenerationofcellulosefibers.

Herein, we report our initial findings of dissolution of cellulose in differentmorpholinium cation based ionic liquid brines. In this study, [BMMorp][Br],[AMMorp][Br],[BnMMorp][Cl]weresynthesizedasstartingmaterials.[BMMorp][OAc],[AMMorp][OAc], [BnMMorp][OAc]weresynthesizedandanalyzed for theirefficacyonthedissolutionofcellulose.Mostoftheseionicliquidscontainedapproximately6wt%water.As the [AMMorp][OAc]‐brinehas showna strongability todissolve cellulose, aseries of N‐allyl‐N‐methyl‐morpholinium salts with different anions were alsosynthesized and analyzed for their efficacy on the dissolution of cellulose, viz.[AMMorp][HSO4],[AMMorp][OH],[AMMorp]2[CO3],[AMMorp]3[PO4]and[AMMorp]‐[H2PO4].

4.1Synthesisofionicliquids

4.1.1SynthesisofN‐butyl‐N‐methyl‐morpholiniumsalts[BMMorp][Br] was prepared in accordance with usual synthetic methods where

uponN‐methylmorpholine was treated with butyl halide in acetonitrile. The productwasobtainedasawhitesolidandrecrystallizedwith2‐propanolandTHF.Thepurityoftheproductwasdeterminedby1HNMR.Sincetheacetateanionhasbeenfoundtohaveapositive impact on the dissolution of cellulose, we then focused our efforts on thesynthesisof[BMMorp][OAc].

4.1.1.1Effectofsolventontheyieldof[BMMorp][OAc]

Initially we tried to synthesize [BMMorp][OAc] using anion metathesis reactionwherein [BMMorp][Br] was treated with sodium acetate in dichloromethane. Nometathesis was resulted in dichloromethane. Moreover, the use of water as solventcould afford only 4% [BMMorp][OAc]. Thus, we decided to use alcohols as solvent.

20

Methanol as solvent resulted in 32% yield of the product while ethanol as solventimproved the yield further to 75%. Importantly, n‐butanol as a solvent increased theyield of product to 90%. Thus, it is evident that alcohols are more favorable formetathesisreactionofbromidewithacetateanion(Figure8).Wealsoattemptedatwostep approach inwhich [BMMorp][Br]was first treatedwith a strongbasepotassiumtert‐butoxidefollowedbyadditionofaceticacid.Nevertheless,themethodfailedtogivehighyieldof[BMMorp][OAc].

Figure8:Theyieldof[BMMorp][OAc]usingdifferentsolvents.1.Dichloromethane;2.Water;3.Methanol;4.Ethanol;5.N‐Butanol.

4.1.1.2IonExchangemethod

In order to obtain high purity [BMMorp][OAc], we changed our strategy to ionexchange approach for the synthesis of [BMMorp][OAc]. Amberlite IR 400 (OH) resinwas employed for this purpose. The resinwas first charged in the glass column. Thesolutionofsodiumacetatewasthenslowlyrunthroughtheresinbed.ThepHofeluentwasslowlychangedfrom14to8whichindicatedthecompleteconversionofOHgroupswith acetate groups. The dilute aqueous solution of [BMMorp][Br] was then slowlychargedontotheresinbed.ThepurityofeluentcollectedineachtesttubewasanalyzedbyIonchromatography.Thetesttubescontainingpure[BMMorp][OAc]weremixedandevaporatedundervacuumat700Cfor3htoremovewatermoleculesandobtainedpure[BMMorp][OAc]asviscousliquid.

Figure9:Pure[BMMorp][OAc]

4.1.3SynthesisofN‐allyl‐N‐methyl‐morpholiniumsalts

21

Wu et al. have synthesized a novel IL 1‐allyl‐3‐methylimidazolium chloride[Amim][Cl] which combined with allyl group which have lower melting point, lowerviscositywhencomparedtootherILssubstitutedbysaturatedalkylcontainingthesamenumber of carbon atoms [76]. A series ofN‐allyl‐N‐methyl‐morpholinium salts weresynthesized. N‐allyl‐N‐methyl‐morpholinium bromide was synthesized as startingmaterial. The ionic liquids based different anions were obtained through two stages.Initially, N‐allyl‐N‐methyl‐morpholinium salts were afforded by to anion metathesisreaction.PureN‐allyl‐N‐methyl‐morpholiniumsaltswereobtainedbytheionexchangemethod.[AMMorp][OAc]wasanalyzedby ionchromatographyand 1HNMR, theothersionicliquidsweredeterminedbyionchromatography.Thepurityofotherionicliquidswasdeterminedbyionchromatography.Theresultsshowedthattherewasnobromidepresentinalltheseionicliquids(detectionlimit≥0.1ppm).

4.1.4SynthesisofN‐benzyl‐N‐methyl‐morpholiniumacetatePernak et al. synthesized N‐benzyl‐N‐methyl‐morpholinium salts using anion

exchangereactionbytwostepmethod,but theyieldwas90.5%[77]. In thiswork, inordertogethigherpurityof[BnMMorp][OAc],threestepmethodwasused.Initially,wefollowedthereportedproceduretoobtain[BnMMorp][OAc]whichpassedthroughthecolumnatlaststep.However,wecouldnotobtainthepure[BnMMorp][OAc],theyieldwasonly92.5%throughourthreestepmethod.

4.1.5.Determinationoftheamountofwaterinionicliquids

Aswateractsananti‐solventforionicliquidsandcanextractionicliquidsintotheaqueousphaseasthewatermoleculesformhydrodynamicshellsaroundtheionicliquidmoleculesinhibitingthedirectinteractionsbetweencelluloseandionicliquidmolecules[58].Therefore,itisveryimportanttoknowtheexactlyamountofwaterinsynthesizedionicliquids.Inthiscase,theamountofwaterinseveralionicliquidswasmeasuredbyKarlFischertitrationmethod.

The analysis showed that (Table3) the amount ofwater present in ionic liquids

wasbetween5‐7wt%.Fortunately,mostoftestedionicliquidscoulddissolvecellulosewithhighcontentofwater.Thismeansthathighamountofwaterintheseionicliquidswouldhavenotnegativeimpacttheirdissolutionabilityforcellulose.Itisnodoubtthatalargeamountofwatercanextractionicliquid,butfurtherexperimentsareneededtodetermine the upper limit of water in ionic liquids which can allow dissolution forcelluloseintheseionicliquids.

Table3:Thepercentofwaterindifferentionicliquids

Ionicliquids WeightPercent(%)

[BMMorp][OAc] 6.63[AMMorp][OAc] 4.95[AMMorp][HSO4] 7.13[BnMMorp][OAc] 6.25

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4.2DissolutionofcelluloseThenewlysynthesizedILswerefurtherprobedforthedissolutionofcellulose.Ina

typicalprocedure for thedissolutionstudies, ionic liquidandcertainamountcellulosewerechargedinthe10mLvialundernitrogenatmosphereandthenplacedintooilbathat different temperatures for different time scale. The dissolution of cellulose wasanalyzedvisuallyandusingopticalmicroscopy.Differentionicliquidswereinvestigatedintermsoftheirabilitytodissolvecellulose.

4.2.1DissolutionofcelluloseinN‐butyl‐N‐methyl‐morpholiniumacetate‐brine

Though,acetate ionsare foundto increase thesolubilityofcellulose in ionic liquid[78‐82], [BMMorp][OAc]‐brine unable to dissolve cellulose against our expectation(Table3).As ithasbeenseenthathalide ionsaregoodhydrogenbondacceptorsandtheir presence facilitates the dissolution of cellulose [55], we decided to employ themixtureof70%[BMMorp][OAc]and23.3%[BMMorp][Br]with6.7wt%waterforthedissolution of cellulose.We started our studywith addition of 2wt% cellulose to theionic liquidmixture andheatedat 80 0C for24h.To our surprise, thismixture coulddissolvethecellulosegivingatransparentsolution.Furtheradditionof2wt%cellulosein the solution with continued heating at 80 0C for 24 h resulted in a transparentsolution leadingtodissolutionof4wt%ofcellulose.Additionof2wt%ofcellulosetothe solution had the same fate. However, the solution now turned viscous enough torestrict the stirringof the solution (Table4). Increasing the amountof celluloseby2wt%didnotbe result in itsdissolutionas itwassuspendedon the topof theviscouspasteofionicliquidandcellulose.Thus,themixtureof70%[BMMorp][OAc]and23.3%[BMMorp][Br]with6.7wt%watercouldabletodissolve6wt%ofcellulose.Theheatingof solution of 6 wt% cellulose in mixture of 70% [BMMorp][OAc] and 23.3%[BMMorp][Br]with6.7wt%waterat800Cfor24halsoresultedinsimilarviscouspasteofILandcellulose.Thus,stepwiseadditionofcelluloseisnotessentialfortheefficientdissolutionofcellulose.

Table4:DissolutionofcelluloseN‐butyl‐N‐methyl‐morpholiniumsalt‐brines

IonicLiquid‐brines Time(h)Cellulose(wt%)

Temp.(℃) Dissolution

[BMMorp][OAc]‐brine 24 2 80 —

70%[BMMorp][OAc]and23.3%[BMMorp][Br]with6.7wt%water

24 6 80 ++

[a]“++”symbolindicatesdissolution;[b]“—”symbolindicatesnodissolution.

4.2.2Dissolutionofcelluloseinorganicelectrolyticsolutions

Recently, Rinaldi reported a new approach of dissolving cellulose in organicelectrolyte solutions containing small fraction of ionic liquid in order to circumventseveraldrawbackssuchasslowerdissolutionduetohighviscosityofionicliquidsandthehighcostofionicliquids[83].Hence,weinvestigatedthedissolutionofcelluloseinN‐butyl‐N‐methyl‐morpholiniumbasedionicliquidswithfeworganicaminesandproticsolventsasadditive.Theamountofadditiveshasbeenvaried from2wt%‐100wt%.

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The organic amines studied as additives were N‐methylmorpholine, N,N,N',N'‐tetra‐methyl guanidine,N,N‐dimethylethanolamine,N,N‐dimethylbenzylamine, 2‐pyrrolidi‐none, N‐methylpyrrolidinone. The protic solvents used were dimethylformamide,ethanoland2‐butanol.

4.2.2.1Theinfluenceofamines

In a typical procedure, 2 wt% cellulose was mixed with mixture of 70%[BMMorp][OAc] and 23.3% [BMMorp][Br] with 6.7 wt% water. A series of organicamineswereusedasadditivesindissolutionofcellulose,suchasN‐methylmorpholine,N,N,N',N'‐tetramethylguanidine, N,N‐dimethylethanolamine, N,N‐dimethylbenzylamine,2‐pyrrolidinoneandN‐methyl‐pyrrolidinone.2wt%oforganicaminewasaddedto itrespectively.Thesolutionwasthenheatedat800Cfor24h.Ifthereisnodissolutionofcellulose,moreorganicaminewasaddeduntil100wt%.Itwasfoundthatnoneoftheorganic amines from the concentrations of 2 wt%‐100 wt% were able to dissolvecellulose, nevertheless, the viscosity of the solutions were gradually reduced withincreasing amount of amine. Thus, all of these amines acted as an anti‐solvent in thedissolutionofcelluloseinmorpholiniumbasedionicliquidmixture.

4.2.2.2Effectofproticsolvents

Interestingresultswereobtainedwhenproticsolventswereemployedasadditiveswithionicliquidmixturefordissolutionofcellulose.AsshowninTable5andTable6,inpresenceof2wt%ethanol, the ionic liquidmixture coulddissolve2wt%celluloseafterheatingat700Cfor24hgivingawhiteviscouspaste.However,furtheradditionof2wt% of cellulose did not lead to the dissolution. Thus,we increased the amount ofethanolby2wt%,nodissolutionwasachieved.Increasingtheamountethanolresultedinthesamefate.

Incaseof2‐butanol,introductionof2wt%of2‐butanolinionicliquidmixturecould

abletodissolveupto4wt%ofcelluloseleadingtoawhitepaste.Increasingtheamountof celluloseby2wt%with increasingamountof2‐butanoldidnot lead to the furtherdissolutioncellulose.Thus,2‐butanolfoundtobemoreefficientthanethanolintermsofdissolution of cellulose inmorpholinium cation based ionic liquidmixture. Dimethyl‐formamide,however,wasunabletoassist inthedissolutionofcellulose inthestudiedionicliquidmixtures.

Table5:Dissolutionofcellulosein70%[BMMorp][OAc]and23.3%[BMMorp][Br]with6.7wt%waterinpresenceofethanol

Temperature(0C)

Time(h)

Ethanol(wt%)

Cellulose(wt%) Dissolution

70 24 2 2 ++

70 24 4 4 —

70 24 6 4 —

70 24 10 4 —

70 24 20 4 —

24

70 24 30 4 —

70 24 40 4 —

70 24 50 4 —

70 24 100 4 —

[a]“++”symbolindicatesdissolution;[b]“—”symbolsindicatenodissolution

Table6:Dissolutionofcellulosein70%[BMMorp][OAc]and23.3%[BMMorp][Br]with6.7wt%waterinpresenceof2‐butanol

Temperature(0C)

Time(h)

2‐Butanol(wt%)

Cellulose(wt%)

Dissolution

70 24 2 2 ++

70 24 2 4 ++

70 24 4 6 —

70 24 6 6 —

70 24 10 6 —

70 24 20 6 —

70 24 30 6 —

70 24 40 6 —

70 24 50 6 —

70 24 100 6 —

[a]“++”symbolsindicatedissolution;[b]“—”symbolsindicatenodissolution

4.2.3DissolutionofcelluloseinN‐allyl‐N‐methyl‐morpholiniumsalt‐brines

Wu et al. reported that 1‐allyl‐3‐methylimidazolium chloride [Amim][Cl] candissolve 5wt% cellulosewithout any pretreatment or activationwithin only 20min[76].Theallylgroupinionicliquidscanacceleratethevelocityofdissolutionofcellulose.A series of ionic liquids based on N‐allyl‐N‐methyl‐morpholinium cation weresynthesizedandusedtodissolvethecellulose.TheresultswereshownatTable7.Oilbath was preheated to preset temperature then vials were put into oil bath. Only

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[AMMorp][OAc]‐brine presented a strong ability to dissolve cellulose, which candissolve 12 wt% cellulose in 20 min at 80 0C and gave a transparent gel. Although[AMMorp][HSO4]‐ brine candissolve 4wt% cellulose under identical conditions,whenthevialwascooled to roomtemperature, themixtureof ionic liquidandcellulosegotstiff. However, if temperature was increased to 120 0C, [AMMorp][OAc]‐brine and[AMMorp][HSO4]‐brine can dissolved 26 wt% and 8 wt% cellulose in 20 minrespectively. The othersN‐allyl‐N‐methyl‐morpholinium salt‐brines have been showntheirnon‐abilitytodissolvecelluloseat800Cfor24h.Figure 10 shows the photographs of cellulose before and after heating in[AMMorp][OAc]‐brine. The color was changed during dissolution of cellulose byincreasingtheweightofcelluloseandincreasingthetemperature.Paleyellowcolorwasshown in the mixture of 2 wt% cellulose with [AMMorp][OAc]‐brine (Figure 11a).When12wt%cellulosewasadded,thecolorofmixturewaschangedtodeepbrownanditwas look like a transparentdeepbrowngel (Figure11b).Veryviscousgel (Figure11c)wasobservedafteradding26wt%cellulosein[AMMorp][OAc]‐brineat1200C.Itisobvioustoseethatadditionofmorecellulosetoionicliquid‐waterbrinesresultedinhigherviscosityofthemixtureandthus,hightemperaturecouldreduceviscosityofthemixturewhichcanacceleratethefurtherdissolutionofcellulose.Table7:DissolutionofcelluloseinN‐allyl‐N‐methyl‐morpholiniumsalt‐brines

[a]“++”symbolsindicatedissolution;[b]“—”symbolsindicatenodissolution.

Figure10:Thephotographsof26wt%cellulosedissolvedin[AMMorp][OAc]‐brine

IonicLiquid‐brinesTime(h)

Cellulose(wt%)

Temp.(0C) Dissolution

[AMMorp][OAc]‐brine 20min 12 80 ++ 22 100 ++ 26 120 ++

[AMMorp][HSO4]‐brine 20min 4 80 ++ 6 100 ++ 8 120 ++

[AMMorp][OH]‐brine 24 2 80 —[AMMorp]3[PO4]‐brine 24 2 80 —[AMMorp][H2PO4]‐brine 24 2 80 —[AMMorp]2[CO3]‐brine 24 2 80 —

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Figure11:Differentweightofcellulosedissolvedin[AMMorp][OAc]‐brineatdifferent

temperature,theimagestakenaftercooling.(a)2wt%celluloseat80℃;(b)12wt%celluloseat80℃;(c)26wt%celluloseat120℃

4.2.4DissolutionofcelluloseinN‐benzyl‐N‐methyl‐morpholiniumacetate‐brine

Pernak etal. prepared a series ofN‐benzyl‐N‐methyl‐morpholinium salts using ananion exchange reaction. The thermal stability, toxicity and ability of dissolution ofcellulose forall thesemorpholinium ionic liquidswereanalyzed [77].They found that90.5% [BnMMorp][OAc] had a best ability which dissolved 1wt% microcrystallinecellulose. We synthesized 86.7 % [BnMMorp][OAc] with 7% [BnMMorp][Cl] and 6.3wt% water and tested the ability of dissolution of cellulose. To our surprised, thesynthesized [BnMMorp][OAc]‐brine had a good ability to dissolve cellulose. Almost 4wt%cellulosewasdissolvedin20minat800C.Whentemperaturewasincreasedto1000Cand1200C,16wt%and22wt%cellulosewasdissolvedrespectivelywithin20min,asshownatTable8.Table8:Dissolutionofcellulosein86.7%[BnMMorp][OAc]with7%[BnMMorp][Cl]and6.3wt%water

[a]“++”symbolsindicatedissolution

4.2.5Analysisofcellulosesolutionusingopticalmicroscopy

4.2.5.1Analysisofcellulosesolutionusingopticalmicroscopyin[BMMorp][OAc]‐brine

The effect of solvents on cellulose fiber structure and the dissolution of cellulose

fiberswereanalyzedbyopticalmicroscopy.AsshowninFigure12A,whencelluloseissocked in water, the cellulosic fibers were clearly seen in microscopic images.Importantly, when cellulose is dissolved in the solution of 70% [BMMorp][OAc] and23.3% [BMMorp][Br] and6.7wt%water and in solutionof 70% [BMMorp][OAc] and23.3%[BMMorp][Br]and6.7wt%waterwith2wt%2‐butanol,fibersweredifficulttoobserve in the microscopic images, which clearly indicated the efficiency of thesesystemsindissolvingcellulose(Figure12B,E).Innoneofthecases,theballooningof

IonicLiquid‐brineTime(min)

Cellulose(wt%)

Temp.(0C) Dissolution

86.7%[BnMMorp][OAc]with7%[BnMMorp][Cl]and6.3wt%water

4 80 ++

16 100 ++ 22 120 ++

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fiberswasseen.Incaseof2wt%celluloseinsolution70%[BMMorp][OAc]and23.3%[BMMorp][Br] and 6.7wt%waterwith 6wt% 2‐pyrrolidinone, cellulosic fiberswereseentofragmentedinsmallerfibersuponheatingat800C(Figure12C).However,fiberstructure remained intactwhen thederivativeofmethylderivativepyrrolidinonewasusedasanadditive(Figure12D).

(A)(B)

(C)(D)

(E)(F)Figure12: Opticalmicrograph of fibers in different solvent systems. (A) Cellulose soaked inwater, (B) 2 wt% cellulose in 70% [BMMorp][OAc] with 23.3% [BMMorp][Br] and 6.7 wt%water,(C)2wt%celluloseinsolutionof70%[BMMorp][OAc]and23.3%[BMMorp][Br]and6.7wt%waterwith6wt%2‐pyrrolidinone,(D)2wt%celluloseinsolutionof70%[BMMorp][OAc]and23.3%[BMMorp][Br]and6.7wt%waterwith4wt%N‐methyl‐2‐pyrrolidinone,(E)2wt%celluloseinsolutionof70%[BMMorp][OAc]and23.3%[BMMorp][Br]and6.7wt%waterwith2 wt% 2‐butanol, (F) 2 wt% cellulose in solution of 70% [BMMorp][OAc] and 23.3%[BMMorp][Br]and6.7wt%waterwith20wt%ethanol.

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The effect of ionic liquid [BMMorp][OAc]‐brinewith increasing in temperature onthe cellulosic fiber structure was also studied using optical microscopy. Figure 13shows microscopic images of 2 wt% cellulose in [BMMorp][OAc]‐brine at differenttemperatures:roomtemperature,40℃,60℃,80℃,100℃. Itcanbeclearlyseenfromthemicroscopicimagesthatwithincreaseintemperature,swellingofmoreandmoreofthefiberstookplace.Thesolventseemstobepenetratinginsidefiberscausingnotonlyswelling the fibersbutalso theouteredgesof the fibers found tobedistinctlypaleascomparedtobrighteredgesatroomtemperature.

(A)(B)

(C)(D)

(E)

Figure13:Microscopicimagesof2wt%cellulosein[BMMorp][OAc]‐brineatdifferenttemperatures:(a)Roomtemperature,(b)400C,(c)600C,(d)800C,(e)1000C.

4.2.5.2AnalysisofcellulosesolutionusingopticalmicroscopyinN‐allyl‐N‐methyl‐morpholiniumsalt‐brines

CellulosicfiberstructurewereanalyzedbyopticalmicroscopyinaseriesofN‐allyl‐

N‐methyl‐morpholiniumsalt‐brines,microscopic imagesshowed that thecellulosecan

29

be dissolved wherein [AMMorp][OAc]‐brine and [AMMorp][HSO4]‐brine. It is clear toseethatthereisnocellulosicfiberstructureinthesemicroscopicimages(Figure14b,c, d) when compared with the microscopic image (Figure 14 a) which presentsmicroscopicimageofcellulosein[AMMorp]2[CO3]‐brinewherecellulosicfiberstructurewasclearlyseen.Astheincreasingtemperature,moreandmorecellulosewasdissolvedin[AMMorp][OAc]‐brineor[AMMorp][HSO4]‐brine.Figure14b,c,dshowthedifferentpercentcellulosein[AMMorp][OAc]‐brineunderdifferenttemperature,butnocellulosicfiberstructurewasseeninbothofthem.

ab

cdFigure14:Microscopicimagesofcelluloseindifferentionicliquid‐brines.(a)2wt%cellulosein[AMMorp]2[CO3]‐brineat400C;(b)4wt%cellulosein[AMMorp][OAc]‐brineat800C;(c)12wt%cellulosein[AMMorp][OAc]‐brineat800C;(d)26wt%cellulosein[AMMorp][OAc]‐brineat1200C.

4.2.5.3Analysisofcellulosesolutionusingopticalmicroscopyin[BnMMorp][OAc]‐brine

It was reported that N‐benzyl‐N‐methyl‐morpholinium acetate has the ability todissolve1wt%celluloseat1000C.However,Tooursurprised,86.7%[BnMMorp][OAc]with7%[BnMMorp][Cl]and6.3wt%waterwassynthesizedbythreestepswhichcandissolved16wt%celluloseunder1000Cand22wt%cellulose at120 0C.MicroscopicimagesofcellulosewereshownatFigure15.Cellulosicfiberstructurecanbeobserved(Figure 15 b) when 24 wt% cellulose dissolved in 86.7 % [BnMMorp][OAc] with 7%[BnMMorp][Cl]and6.3wt%waterat1200C.

30

abFigure15:Microscopicimagesofcellulosein86.7%[BnMMorp][OAc]with7%[BnMMorp][Cl]and6.3wt%water:(a)10wt%celluloseat80℃;(b)24wt%celluloseat120℃.

4.3Regenerationofcellulose

Regeneratedcellulosecanbeobtainedduringtherecoveryofionicliquids.Whenthegel material was subjected to methanol, the ionic liquids were extracted by themolecular solvent. At the same time the gel material was changed to white beads(Figure16a).Apaleyellowthinfilmwasobtainedafterusingglassslideandcoverslipfor cellulose restructuring. A colorless film was obtained after the film was washedseveral times using distilled water (Figure16b). However, this film was not stable.Whendryingthecolorlessfilmat80℃for10min,awhitecellulosefilmwasobtained.

Figure16: Photographs of regenerated cellulose. (a) Regenerated cellulose in extracted ionicliquid;(b)Filmofregeneratedcelluloseinwater;(c)Filmofregeneratedcellulose.

4.4Recoveryofionicliquids

 Asolutionwasobtainedafter filtrationduring theregenerationof cellulose,whichcontained an ionic liquids and the anti‐solvent (Figure17b). In thiswork,methanolwas added into the gel material as the anti‐solvent. Methanol was evaporated undervacuumandtheresidualwasanalysizedbymeansof1HNMR.OnthebasisoftheNMRdata,nodecompositionwasobserveduponcellulosedissolution‐regeneration cycle in[AMMorp][OAc] .For further investigationof thedissolutionabilityof this ionic liquidforcellulose,recovered[AMMorp][OAc]wasusedinanothercycle.4wt%cellulosewasquicklydissolvedat80 in20min.Thus,therecovered[AMMorp][OAc]stillpossessed

31

astrongabilitytodissolvecellulose.TheFigure17showstheextractedionicliquidinmethanolandrecoveredionicliquid.

Figure 17: Recovery of ionic liquids. (a)recovered ionic liquid; (b) extracted ionic liquid inmethanol.

5.Conclusions

Inconclusion,aseriesofmorpholiniumcationbasedionicliquidswerepreparedbydifferent synthetic methods in normal bench‐top laboratory conditions. Amongstvariousinvestigatedsolventsduringtheanionmetathesisofbromideiontoacetateion,n‐butanolwasfoundtobethemostefficientsolvent.However,thepure[BMMorp][OAc]couldonlybeobtainedviatheionexchangemethod.Asaconsequence,theotherionicliquidswerealsosynthesizedapplyingtheionexchangemethodasthelaststep.

Qualitative cellulose dissolving experiments with morpholinium ionic liquids

showedthat[AMMorp][OAc]‐brineexpressedstrongefficacyfordissolutionofcellulosewithoutanypretreatment.AmongaseriesofN‐allyl‐N‐methyl‐morpholiniumsalt‐brines,only [AMMorp][OAc]‐brine and [AMMorp][HSO4]‐brine showed the ability to dissolvecellulose, but [AMMorp][HSO4]‐brine express the lower power for dissolution ofcellulose when compared to [AMMorp][OAc]‐brine. This again demonstrated thesuperior ability of acetate‐based morpholinium ionic liquids to dissolve cellulose, incomparison to the corresponding evaluated alternatives containing other anions. Thecombination of [BMMorp][OAc]‐brine with [BMMorp][Br] and [BnMMorp][OAc]‐brinewith [BnMMorp][Cl]werealso found tobecellulosedissolvingsolvent,whichshowedtheeffectofhalideionsduringdissolutionprocessofcellulose.

Differentsubstituentgroupinacetate‐basedmorpholiniumionicliquidsalsoimpact

the ability of dissolution of cellulose. Among these ionic liquids, the allyl groupdemonstrated a strongerpositive effect for cellulosedissolution than eitherbenzyl orbutyl group. Extraction and recovery of [AMMorp][OAc] was carried out and therecovered [AMMorp][OAc] demonstrated a strong ability to dissolve cellulose. Theregeneratedcelluloseshowedagoodphysicalstabilityasadriedfilm.

Theuseofdifferentadditivestocellulosedissolvingmixtureof[BMMorp][OAc]with[BMMorp][Br] and water showed very interesting results. None of the investigated

32

amines were able to assist the dissolution of cellulose; rather they acted as an anti‐solvent. Importantly, ethanol and 2‐butanol helped in dissolving cellulose to certainextent.Micrographicstudiesofvarioussamples indicated thatcertainsolventsystemsbringaboutfragmentationofthecellulosicfiberswhileotherkeepsthecellulosicfiberintact at high temperature. The absence of fibers in the micrographic image of thecellulosic solution gave an indication of cellulose dissolution in the solution.Micrographicstudiesofdissolutionofcellulosein[BMMorp][OAc]‐brinesuggestedthatthefibersweremoreexpansivelyswelledwithincreaseintemperatureofthesolutionindicatinggreaterpenetrationofsolventwithriseintemperature.

33

6.Acknowledgement

Thanks to Prof.Jyri‐PekkaMikkola, for allowingme to join your researchgroup to complete my master’s thesis; I learned many practical labexperiencesdruingtheresearchandforthefirsttimeIcametocontactwithcelluloseandionicliqiudsbothareveryinteresting

Thankyou,Dr.DilipRaut, for supervisingmywork,thankyou for sharing

your excellent knowledge in organic chemistry with me and the skilfulguidinginmyresearch.Thankyouforyourunderstanding.

Thank you, William Larsson,for the excellet guiding in equipments and

instruments,particularlyinionchromatogrphy,thankyouforteachingmemanylabskills.

Thanks to JohnGräsvik for sharing your chemicals and fume hood, your

kindnessmakethereseachmorequickandmoreconvenient. ThankstoGordonDriverforguidingincaculationofresin,duetoyourhelp,

thecolumnwasmadewhichcangetthepureproduct. Iwould also like to thankNatalia Bukhanko , Kumar Samikannu,Mikhail

Golets,JohanAhlkvistandKrisztianKordas forofferinganyconvenienceinthelab,thankstoallthemembersofJ.P.Mikkola’sgroup.Itismyhonortoknowyou!

I would like to thank Bertil Eliasson for advices in courses, projects and

rules,thankstoPatrikAndersson,SolomonTesfalidet,andsoon,whowerethe supersiors in different courses . I'm very thankful for all the teacherswhotaughmeandmyfellows.

Finally, many thanks to the Government of Sweden and Ministry of

EducationofSwedenforfreetuitionfeesupportduringmymaster’sstudysincefrom2011theinternationalstudentsfromNoN‐Europeancountrieshavetopayatutitionfee.Iamverymuchenjoyingthestudyandlifeinthisbeautifulcountryalthoughsometimesmakingfewmisunderstanding duetothelanguage!

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