Catalysis in Ionic LiquidsGeneral observations and

examples from own recent work

Dirk De Vos, Charlie Van Doorslaer, Igor Ignatyev,Pascal Mertens, Koen BinnemansPascal Mertens, Koen Binnemans

Centre for Surface Chemistry and CatalysisFaculty of Bioscience Engineering, K.U.Leuven

Leuven Summer School Ionic Liquids

1

Part A. General Introduction to catalysis in Ionic LiquidsEffects of ILs on catalytic reaction pathways

Water, protonsMany ILs are hygroscopic, and the water may poison the catalysts;Halide impurities in ionic liquids can strongly coordinate to metals,

and have a poisoning effect as well;

Protons of protic ILs can have a promoting effects on reactions (acting as a ‘proton reservoir’)e.g. in the Pd or Rh catalyzed dimerisation of methyl acrylate

When halide dissociation from a complex is a rate determining step, this stepmay become problematic in ILs with a low solvation capacity for Cl-. E.g., in [bmim][TfO], Cl- dissociation from Ru(II)-X-arene-diphosphineis very slow, but this can be speeded up by water addition.

2

BasesILs may contain unreacted amines (e.g., 1-methylimidazole) and these can

enhance the basicity of some catalysts. For instance, the enhanced activityof L-proline or piperidine has been explained in this way.

Residual 1-Methylimidazole has also been proposed to play a role in stabilizing metal nanoparticles.

ILs as additives to ‘conventional’ solvent reactionsILs as additives to ‘conventional’ solvent reactionsIn some cases, adding minor amounts of IL can have unexpected effectse.g. some cellulases or lipases are completely inhibited in ILs, but for instance

a small amount of [bmim][BF4] improved lipase activity in a transesterification. Why = ?

3

Complex formation with anionsIn the absence of stronger ligands, even ‘inert, weakly coordinating’ anions

could bind to the metal complexes:

.. Such phenomena could also explain unexpected dissolution of catalysts... Such phenomena could also explain unexpected dissolution of catalysts.

In some cases, this coordinating ability can even stop the activity, e.g. the Ni-diimine catalyzed ethene oligomerization is stopped by Tf2N-.

But the activity can also be enhanced, e.g. Ni + chloroaluminates:

4

Complex formation involving the cations:

Especially with imidazoliums, the acidity of C(2)-H plays a role. N-heterocycliccarbenes (NHC)can be formed, even in the absence of a base. NHCs are(very roughly) similar to phosphines in their coordinating ability, meaningthat they can act as a ligand for many complex catalysts.E.g. Pd-carbenes are good (pre)catalysts for Heck, Suzuki couplings

Typical check: replace imidazoliums with C(2)-H bydialkylimidazolium substituted at C2alkylpyridinium compounds etc.

Example of a proposed mechanism of carbene formation:

5

Formation of highly active species:

Sc(OTf)3 is a moderately good Lewis acid catalyst, but surprizing acceleratingeffects have been found :

This has been explained by formation of new, more electrophilic Lewis acids,e.g. [Sc(OTf)3-x][SbF6]x

Lee et al., Accs. Chem. Res. 2010, 985

6

Stabilization of reactive intermediates in ionic liquids

The well-known [bmim]Cl-AlCl3 IL (with xAlCl3 = 0.67) has a strong promotingeffect on heterogeneously catalyzed hydrogenations that are difficult toachieve in mild conditions: ambient conditions !

Proposed intermediate:

Lee et al., Accs. Chem. Res. 2010, 985 7

Some starting points in the IL-catalysis literature

Parvulescu and Hardacre, Chemical Reviews 107 (2007) 2615-2665

Magna, Bourbigou, Applied Catal. A 373 (2010) 1-56

De Maria, Angew. Chem. Int. Ed. 47 (2008) 6960(mainly on organo- and biocatalysis)

Lee, Song et al., Accs. Chem. Res. 43 (2010) 985

Plechkova and Seddon, Chem. Soc. Rev. 37 (2008) 123

…

8

Part B. Supported Ionic Liquid Phases:At the crossroads of IL technology and Heterogeneous catalysis

In a supported ionic liquid phase (SILP) catalyst system, an ionic liquid (IL)film is immobilized on a high-surface area porous solid, and a homogeneouscatalyst is dissolved in this supported IL layer.This approach potentially combines the attractive features of homogeneous catalysts with the benefits of heterogeneous catalysts. Typically, there is no direct interaction between the homogeneous catalyst and

Leuven University

Typically, there is no direct interaction between the homogeneous catalyst and the support surface, and thus, the molecular control over the catalytic activity is well maintained.

Pioneer: Peter Wasserscheid

A profound analogy exists with supported aqueous phase (SAP) catalysis: a thin filmof catalyst-bearing water, dispersed on a solid like silica. However, water is too volatile for operation in a continuous gas phase reactor and this entails a risk of catalyst degradation and deactivation of the system.

9

General advantages of SILP systems

Surface / Volume ratio is increased→ easier diffusion of substrates to the IL-dissolved catalyst;→ easier diffusion of gaseous reagents (H2, O2, CO, …)

.. think of the limited solubility of these gases in many ILs !→ higher viscosity of IL is more easily dealt with.

Smaller amounts of ILs suffice than in classical biphasic liquid/liquid reactions;

Can be operated in gas phase or liquid phase reactors;

Classical advantages of heterogeneous catalysis <> homogeneous catalysisfacile catalyst recuperation ;continuous operation

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Catalyst / Ionic Liquid / Support Combinations

Type 1: true, separate IL phase; with the IL as a multilayer on the support

1a: prepared via impregnation of IL on asupport;metal/ligand are first dissolved in IL;

1b: support surface is first covalently modified1b: support surface is first covalently modifiedwith an IL fragment;additional IL + catalyst are added.

Type 2: monolayer of directly anchored IL fragments, e.g. via

covalent grafting,sol-gel synthesis, using XSi(OR)3

≠ true SILP,= covalently attached ligand

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Catalyst / Ionic Liquid / Support Combinations

Type 2 (ctd.):Most often, the cation is anchored;The anion can then partially be replaced by anionic catalysts, e.g.

WO42-, RuO4

-, PdCl42-, NiCl42-,CuCl42-, Al2Cl7-, SnCl5-

= supported ionic liquid catalysts or SILCs= supported ionic liquid catalysts or SILCs

Type 3Ionic liquid is impregnated on the surface ofa classical heterogeneous catalyst(e.g. Pd/CaCO3, Ru/C, …)= solid catalyst with ionic liquid layer or

SCIL

further focus mainly on type 1 (true SILPs) 12

Remarks / requirements on the homogeneous catalyst in the SILP

Preferably long lifetimeno loss into the organic layer

Ionic liquids are highly suited to hold polar species, e.g. PdCl42-, WO4

2-

Affinity of the catalyst for IL can be increased by introducing ionic groupsAffinity of the catalyst for IL can be increased by introducing ionic groupssulphonates as anionic groups in phosphine ligandsguanidinium, imidazolium or pyridinium as cationic groups

Even metal nanoparticles, or enzymes can be entrapped in the SILP

Popular metal complexes: based on Rh or Pdbecause immobilization via other routes is problematic(e.g. they easily give leaching when immobilized via other routes)

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Remarks / requirements on the ionic liquid in the SILP

Desired high solvation power for the complexesweakly coordinating properties

as in [bmim][BF4], [bmim][PF6] vs. electrophilic cat.sbut also water stability, low viscosity

Popular emim, bmim, hmim as cationsPopular emim, bmim, hmim as cationswith Cl- and Br-: hydrophilic ILswith BF4

-, PF6-, (CF3SO2)2N-: hydrophobic ILs

Problemsare well known (cfr. KS)note that fluoride from hydrolysis can be a catalyst poisonwater content is therefore an important concern

Alternatives imidazoliums + alkylsulfates14

Remarks / requirements on the support in the SILP

Typically SiO2, silica gels with surface area of 300–500 m2g-1

Thermal pretreatment → lower number of acidic silanols (SiOH may react with catalyst !)

Alternatives ordered mesoporous SiO2 materials, e.g. with parallel cylindrical pores (‘MCM-41’)with parallel cylindrical pores (‘MCM-41’)with a 3-D pore system (cubic ‘MCM-48)

zeolites, clays like montmorillonitelower surface materials: Al2O3, TiO2, ZrO2 etc

TiO2 is more hydrolysis stable than SiO2

Al 2O3 is more stable at high pH than SiO2

organic polymer materials e.g. poly(diallyldimethylammonium Cl), PS-basedchitosan

carbon nanofibres etc 15

Catalyst preparation

TypicallyCatalyst and IL are dissolved in a common solvent, and dry support is added

e.g. THF, DCM, MeOH, …Volatile solvent is removed under reduced pressure

AlternativelyAlternativelyImpregnation of [IL+catalyst] on a support pre-functionalized with an IL layer

Characteristicscatalytic metal loading 0.01-0.2 mmol g-1

molar ligand/metal ratio (L/M) to be adaptedIL loading 10-25 wt.%pore filling degree (α) << 100 % (thin IL layer)

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Conditions of SILP use

Gas Phase fixed bed reactor = idealrisk for leaching of complexes : practically zero (exceptions ?)polarity of reaction products should not be so high as to impede

evaporationhigh thermal stability, low vapour pressure

Liquid phase catalysis(i.e. a liquid flow passing along the SILP catalyst)

- requires delicate tuning of polarities of all constituents to avoidleaching of ionic liquid or catalyst to passing flow

→ IL should have extremely low solubility in solvent/productThus alkanes, or DCM in combination with ‘polar’ ILs

water, EtOH, .. in combination with triflimide-based Ils

- physical removal of the IL from the support must be avoided → keep the pore filling degree with IL sufficiently low 17

Conditions of SILP use

Supercritical CO2 as a solventCO2 dissolves very well in most IlsConversely, most ILs do not perceptible partition into sc CO2

scCO2 reduces the viscosity of the IL thus improves the solubility, mass transport of permanent gases. thus improves the solubility, mass transport of permanent gases.

Disadvantages of scCO2high investment and operating costs lower solvating ability than for classical organic solvents.

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Selected Examples. 1. Hydroformylation; liquid phase

With Rh: mild conditions (100 °C, 15 bar CO/H2)simple precursor, e.g. Rh(CO)2(acac) (acac = acetylacetonate) as the precursor phosphine ligands to favour the formation of linear over branched aldehydes

tppts

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Support: SiO2 gel preheated at 300°Creacted with [1-Bu-3-(3-triethoxysilylpropyl)-4,5-dihydroimidazolium][BF4] → SiO2 gel pre-functionalized with IL fragments

0.4 IL fragments per nm2, or 35 % of all SiOH’s

Typical SILP system for liquid phase hydroformylation(after C. P. Mehnert et al., J. Am. Chem. Soc., 2002, 124, 12932)

Next:add solution in acetonitrile of

Rh(CO)2(acac),tri(m-sulfonylphenyl)phosphine.Na3 (tppts)(optionally) tri(m-sulfonyl)triphenyl phosphine (bmim)3

+ extra [bmim][BF4] or [bmim][PF6]

Solvent evaporation → free flowing powder20

Reactions in the liquid phase (batch / continuous mode)

At 100 °C and 100 bar CO/H2: • TOF (65 h-1) is ~3 times higher than in comparable biphasic IL/solvent system

because of higher concentration of active Rh at interface

• n/iso ratio was (as expected) comparable• the catalyst is intrinsically insoluble in the organic medium (aldehyde product),

but the non covalently bonded IL (bmim BF4) displayed some leaching to the aldehyde,and thus entrains the catalyst !

• Activity of the SILP catalyst tends to decrease with increasing chain length of the olefin,due to poorer solubility of the olefin reactant.

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2. An improved hydroformylation catalyst for gasphase use:Rh(CO)2(acac)/ sulfoxantphos / [bmim][n-C8H17OSO3]

• SiO2 support was thermally pretreated to limit effects of silanols;• Xantphos type ligands have a very high ‘bite angle’, and thus push up the

n/iso ratio• Sulfonation of xantphos

→ good dissolution in the IL• [bmim][n-C H OSO] as an optimal IL• [bmim][n-C8H17OSO3] as an optimal IL

Performance:• 200 h time-on-stream, with only a slight decrease in activity

Hypothesis: higher MW side-products, e.g. aldols, pollute / dilute the ILActivity can somewhat be restored by vacuum treatments

• n-selectivity: ~97 %; constant over the run• Rh concentration in exit gas streams below 3 ppm detection limit (!)• Rates are higher for butene than for propene

Relation with solubility of olefins in [bmim][n-C8H17OSO3] P. Wasserscheid, Adv. Synth. Catal., 2007, 349, 425

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3. A SILP hydroformylation catalyst for sc CO2 use:Rh(CO)2(acac)/TPPMS- (monosulphonated TPP), PrMeIm + salt /[OctMeIm][Tf 2N]

Performance:• TOFs up to 800 h-1 in 1-octene hydroformylation (100°C, 100 bar total pressure)• at least 40 h time-on-stream, • at least 40 h time-on-stream, • sc CO2 decreases viscosity and improves diffusion;• Kinetic experiments showed that diffusion is not rate limiting

→ all reaction centres can be reached and used• scCO2 extraction helps in avoiding accumulation of heavies in the SILP

D. J. Cole-Hamilton, Chem. Commun., 2007, 1462

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4. A methanol carbonylation catalyst

[Rh(CO)2I]2 + [bmim][I] (excess) → [bmim][Rh(CO)2I2] in [bmim][I]

Performance:• gas phase reaction • TOF: 76 h-1

• high conversion, • little by-products

A. Riisager, B. Jørgensen, P. Wasserscheid and R. Fehrmann, Chem. Commun., 2006, 994.

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5. Olefin metathesis using Grubbs’ catalyst

SILP system: [hmim][PF6] + first generation Grubbsin the pores of amorphous alumina

Grubbs catalyst is sensitive to nucleophiles. Hence water and EtOH are not suitableas solvents (complete deactivation). By contrast, aromatics like benzene are OK as solvents. Whether this ensures nice phase separation is a critical issue.

Performance:• Best result: TON 154, 82% yield from diethyl diallylmalonate• Reuse: 82 % yield in 1h upon first use ,

70 % yield in 2 h after the 5th recycle.

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6. SILP catalyst for urea formation

SILP Preparation by sol-gel processTEOSTEOS[1-alkyl-3-methylimidazolium][BF4] aq. HCl, EtOH, 60°C → gel !Rh(PPh3)3Cl dried at 150°C

Performance:• at 180 °C and 50 bar CO: very high TOF and conversion• best stability with decylmethylimidazolium IL• alternative reaction (under additional O2 !):

MeOH + aniline + CO → methyl N-phenylcarbamateF. Shi, Q. Zhang, D. Li and Y. Deng, Chem. Eur. J., 2005, 11, 5279. 26

7. Pd-catalyzed coupling reactions

Role of the IL can be manyfold:• N-based cations could stabilize nanoparticles• Imidazoliums could be carbene precursors• .. Or ‘just’ a solvent ?

Example: SILP for Mizoroki-Heck reaction

SILP: Pd(OAc)2 and [bmim][PF6] on N,N-diethyl-aminopropylated silica gel

Performance:

! 5 times reused; leaching only 1.1 ppm of Pd after first run.Using water as the extracting agent allows to remove R3N.HI by-product fromthe SILP phase.

Chem. Commun., 2005, 2942

27

8. Organocatalysis in SILPs

SILP preparation:• SiO2 modified with [1-(3-trimethoxysilylpropyl)-2,3-dimethylimidazolium][BF4]

or [1-(3-trimethoxysilylpropyl)-4-methylpyridinium][BF4] • Next: extra [bmim][BF4] or [1-butyl-4-methylpyridinium][BF4] ,

(L)-proline(L)-proline

Reaction:asymmetric aldol

Ee’s were similar to those in classical solvents (e.g. DMSO)Gruttadauria et al. Tetr. Lett. 2004, 6113

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9. Asymmetric metal complex catalysis in SILPs

Many ‘classical’ enantioselective catalysts now have been used within SILPs, e.g. Ru-BINAP + [bmim][PF6]

As a support, the polymer poly(diallyl-dimethylammonium chloride) was used.The system was less active than Ru-binap in one organic phase (2-PrOH),but more active than a biphasic mixture containing an IL.

Many asymmetric hydrogenations require base activation, e.g. with KOtBu, K2CO3, ..• SILP support can be pretreated with such as base; • Ammonium cations can be replaced by phosphonium: these are more stable at

high pHK. L. Fow, S. Jaenicke, T. E. Müller and C. Sievers, J. Mol. Catal. A, 2008, 279, 239

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Conclusions on SILP catalysis

Attractive features high activity and selectivityease of product separationefficient catalyst recycling

To be developed / further understoodtuning of polarities in liquid – liquid systemstuning of polarities in liquid – liquid systems

… especially when highly polar products are formed !interaction between support / IL / catalyst ?are the systems really superior to existing ‘classical’ ones ?

These thoughts / examples … to be read soon in Van Doorslaer, De Vos, et al., Dalton Transactions (2010):a review paper on SILP catalysis

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Part C. Examples from our own recent work:reactions in ionic liquids / strategies for product isolation

1. Reactions with spontaneous product segregation ����hydrogenolysisalcohol oxidation

2. Ozonations in ionic liquidsincl. membrane separations

Leuven University

incl. membrane separations

3. Renewables utilization in ionic liquidssorbitol from cellulosealkylglycosides from cellulose

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Leuven University

CF3 S

N

O

O

CF3

OOS

-N

COOH+

IL = alternative for volatile organic solventsin catalytic reactions

Negligible vapor pressure

High electrochemical stability

High thermal stability

Low flammability

New reactions in ionic liquids

IL = alternative for volatile organic solventsin catalytic reactions= ‘designer solvents’

1. 90% of catalytic reactions performed in [BMIM][BF4] and [BMIM][PF6]

IL adapted to the needs of a reaction, with easy recycling of the ionic liquid:

2. Separation of reaction products from IL after reaction = problematic

however …

1. Reactions with spontaneous product segregation ����

2. Ozonations in ionic liquids3. Renewables utilization in ionic liquids

32

Reaction: ketone hydrogenolyis Selection candidate ILs

Condition 1: desired mixing behaviour (T switch) !

Condition 2: IL bearing an acidic function!

KatILS

P P

ILKatKat

ILS

P

CatILS

P P

ILKat

P

ILCat

products

O

R

OH

R

RR

Pd

Pd

H+

H2

H

Classic Ammonium, imidazolium, pyrrolidinium IL: No IL with desired phase behaviour except [BMPyr][dicyanamide]

Choline and betaïnium based IL: 5 ILs with desired phase behaviour, mostly polar

ILILIL

Reaction T Room T IL + catalyst (Cat)recycled

36 IL tested (ammonium, imidazolium, pyrrolidinium,…)

H2

33

60

80

100[%] X

[%] S

N

OH+

Tf2N-

N

COOH+

Tf2N-

N

COOH+

Tf N-

N

OH+

Tf2N-

Before reaction

After reaction in

Reaction results TEM

0

20

40

[Chol][Tf2N] [Hbet][Tf2N] [Chol][Tf2N] +[Hbet][Tf2N]

% Tf2N- After reaction in

[Chol][Tf 2N]

Binary mixture superior! Colloid stabilization by Quat’s34

Hydrogenolysis of aromatic ketones under optimized reaction conditions[a]

Ketone Ketone/IL [mol/mol]

catalyst Time [h]

X[b]

[%] S[c]

[%] acetophenone 0.52 Pd-Y 2 100 99.9

acetophenone[d] acetic acid Pd-C 2 100 87 butyrophenone[e] 3.14 Pd-C 2 100 97 butyrophenone[d] acetic acid Pd-C 2 99 69

>99% conversion at > 94% selectivity

butyrophenone[d] acetic acid Pd-C 2 99 69 octanophenone 0.52 Pd-C 4 99 94

octanophenone[d] acetic acid Pd-C 2 99 62 [a] Reaction conditions: [Hbet]/[Chol] (mol/mol) = 0.5, 0.08gcatalyst (5 wt% Pd), 80 °C, 50 bar H2.[b] X [%] = conversion of ketone.[c] S [%] = selectivity towards alkylbenzene.[d] Reaction performed in acetic acid (2mL) as solvent.[e] After 1 h the reactor was re-pressurized with 50 bar H2.

35

80

100[%] X

[%] S

1st recycle 2nd recycle

product

Simple product isolationby decantation

Efficient catalyst recyclingwithout loss of activity or selectivity

Product separation and IL/catalyst recycling

0

20

40

60

0,08g 5%Pd-Y in IL 1st recycle 2nd recycle

%

product

IL + catalyst

ICP-AES: no leachingof catalyst in product phase!

Phase separation after cooling to 25 oC

temperatureswitchpolarity switch

Van Doorslaer et al., ChemSusChem, 2008, 1(12), 997 36

R R'

OH

R R'

O+ 0.5 O2 + H2O

Pdn+

Reaction: alcohol oxidation Selection candidate IL

Condition 2: oxygen stability!

Condition 1: desired mixing behaviour!

KatIL

S

P

KatIL

S

P

CatIL

A

K P

ILKat

P

ILKat

Ketone(K)

Cat

ReactionT 25°C25°C

S

ILKat

S

ILKat

Alcohol(A)

CatIL IL

K

KatIL

S

P

KatIL

S

P

CatIL

A

K P

ILKat

P

ILKat

Ketone(K)

Cat

ReactionT 25°C25°C

S

ILKat

S

ILKat

Alcohol(A)

CatIL IL

K

Secundary alcohols:2-C4-ol, 2-C6-ol, 2-C8-ol, 2-C10-olPrimary alcohols: 1-octanol

Desired phase behaviour with full range of alcohols:

[EMIM][EtOSO 3] [EMIM][TsO] [EMIM][MeSO 3] [BMIM][BF 4]

Recycle Catalyst (Cat) and Ionic Liquid (IL)Recycle Catalyst (Cat) and Ionic Liquid (IL)29

Tos-EtOSO3- MeSO3

- BF4-

+ + +Bu

+

37

Reaction results

Alcohol P(O2)/bar Y(%) TON[c]

1 2-butanol 10 11 112 2-hexanol 10 16 163 2-octanol 10 76 764 2-decanol 10 83 835 2-dodecanol[d] 10 21 216 2-octanol 30 66 6620

40

60

80

100Y (%)

TON

Nature of IL Chain Length, oxygen pressure

6 2-octanol 30 66 667 2-decanol 30 64 648 2-dodecanol 30 49 49

alcohol (10mmol), [BMIM][BF 4], mass ratio IL/alcohol =1,Pd(OAc)2 (molar ratio substrate/catalyst = 100), 120°C, 24h;

0

20

[BM Im][BF4] [EM Im][Tos] [EM Im][EtSO4] [EM Im][M eSO3][BMIM][BF 4] [EMIM][EtOSO3]

[EMIM][TsO] [EMIM][MeSO 3]

2-octanol (10 mmol), ionic liquid, IL/alcohol = 1,substrate/Pd = 40, 120°C, 10 bar O2, 24 h

38

After optimizing choice ionic liquid and the reaction conditions[a]

[a] Reaction conditions: alcohol (10mmol), Pd(OAc)(S/cat = 40), 120 oC, 24h;

2-ketone

Octanoic acid + 1-octyl octanoate

Entry Alcohol IL IL/A P(O 2)/bar Y(%) 1 2-octanol [BMIM][BF 4] 1 10 79 2 2-octanol - 0 10 63 3 2-decanol [BMIM][BF 4] 1 30 87 4 2-decanol - 0 30 39 5 1-octanol [EMIM][TsO] 1 30 12 + 83

Reaction results

Secundary alcohols converted for≥ 79%, 100% selective towards ketone

[a] Reaction conditions: alcohol (10mmol), Pd(OAc)2 (S/cat = 40), 120 oC, 24h; 1-octyl octanoate

Primary alcohol converted for ≥ 95%, with a 83% yield of 1-octyl octanoate

Despite the relatively low gas solubility in ILs, the presence of the IL positively impacts on the reaction yield.

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Recycling IL / catalyst:without significant loss in actvity

Product separation and catalyst recycling

Simple product isolationby decantation

Product phase

Run Alcohol C(%) S(%)

1 2-octanol 79 100

2 2-decanol 70 100

Reaction conditions: alcohol (10 mmol),Product phase

IL + catalyst

Product phase: less than 0.01mol% IL leaching (NMR)no measurable Pd leaching(ICP-AES)

Van Doorslaer et al., Phys. Chem. Chem. Phys., 2010, published online, DOI 10.1039/b920813P

Reaction conditions: alcohol (10 mmol),[BMIM][BF 4], mass ratio IL/alcohol =1,Pd(OAc)2 (molar ratio substrate/catalyst = 40),120°C, 10 bar O2, 24h;

40

� Very low vapor pressure

Disadvantages O3

� Explosive nature O3

Ionic liquids = solution

R R1 2

aldehydes, acids, ..O3

OHOH

OH

OOH

OMe

OHOH

OH

OHOH

COOMeO3

ββββ

2. Ozonations in ionic liquids

O O

O3

O

OOH

O

OOH

OO3

+ OH2

O O

+ CH3 OH

O3

MTP

hydroxy-ester carboxy-ester

lactone

� Higher η

� Higher γ

� Explosive nature O3

�Aerosol formation

Selected model reaction:

41

Selection of ionic liquids for MTP ozonation:

• Sufficiently low melting point;• Oxidation and O3 stable !

Unstable:

Stable:

Cl-Bu

+

AcO-

+

CF3COO-

+etc

N+

N(CN)2-

Stable:

mp < -50°C

N+

S NS

CF3

CF3

O

O

O

O

-

NMe

R R+ Cl-

[[[[BMPyrr ][][][][Tf2N]

[[[[BMPyr ][][][][N(CN)2]]]][[[[Benzalk][][][][Cl]

42

0

20

40

60

80

100

0 1 2 3 4 5 6

hydroxy ester

lactone

condensation product

0

20

40

60

80

100

0 1 2 3 4 5 6

hydroxy ester

carboxy ester

Acetic anhydride IL: [BMPyr][N(CN) 2]

MTP Ozonolysis in organic solvents vs ionic liquids

OH-esterlactoneby-product

OH-esterlactone

0 1 2 3 4 5 6

R eact io n t ime/ h

0 1 2 3 4 5 6

R eact io n t ime/ h

[MTP] = 5 mol L-1; [O3] = 40 g/m3; 25°C

1. Acetylating solvent needed

2. Low T (-78°C):� Control selectivity� Prevent solvent loss

3. Product separation: destillation

1. NO acetylating solvent needed

2. Wide T range possible

3. Product separation via membrane filtration

4. Higher yields

[MTP] = 5 mol L-1; [O3] = 40 g/m3; 25°C

43

40

60

80

100

5gm-3

20gm-3

40gm-3

60gm-3

20-80 g/m3

5 g/m3 in [BMPyr][N(CN)2]

Effect of ozone concentration:

0

20

0 1 2 3 4 5 6 7 8R eac t io n t im e / h

20-80 g/m3

lower O3 availability: Higher selectivity towards hydroxy esterdue to less overoxidation to carboxy ester

[MTP] = 5 mol L-1; [O3] = 5 g/m3; 25°C

Van Doorslaer et al., Chem. Commun., 2009, 42, 6439 44

40

60

80

100Y

ield

(%)

hydroxy ester

carboxy ester

total yield ester

40

60

80

100Y

ield

(%)

hydroxy ester

carboxy ester

total yield ester

422.4 g/mol208.3 g/mol

Methoxypyran ozonolysis in various ionic liquids

0

20

40

[BMPyr][N(CN)2] [BMPyr][Tf2N] [BenzAlk][Cl]

Ionic liquid

Yie

ld (%

)

[BMPyr][N(CN)2] [BMPyr][Tf2N] [BenzAlk][Cl]

0

20

40

[BMPyr][N(CN)2] [BMPyr][Tf2N] [BenzAlk][Cl]

Ionic liquid

Yie

ld (%

)

[BMPyr][N(CN)2] [BMPyr][Tf2N] [BenzAlk][Cl]

[MTP] = 5 molL-1; 80 °C; 1 h; 40 g/m3 O3-flow

For Solvent resistant nanofiltration: ‘Higher MW’ [BMPyr][Tf 2N] preferred

45

Product separation applying solvent resistant nanofiltration

Polymeric ‘hydrophobic’ membranes

Membrane p (N2) (bar) RIL (%)[b] Permeability

(L/m2 h bar)

Zeol-PDMS/PI2 20 90±2 0.7±0.3

DuraMemTM 200 40 95±2 0.15±0.075

[a] Filtration conditions: 1000 RPM stirring, T = 20 °C;[d] rejection IL = RIL = ((1-CP)/CF) * 100 %) .

Testmixture

IL product

[d] rejection IL = RIL = ((1-CP)/CF) * 100 %) .

96% rejection IL

Filtration step

RIL (%) Permeability (L/m2 h bar)

1 71±2 0.175±0.07

2 94±2 0.275±0.07

3 96±3 0.425±0.09

Reaction conditions: 2g of [BMPyr][Tf2N], 10 mmol of MTP, 80 °C, 40 g/m3 of ozone;

Reactionmixture

Van Doorslaeret al., Green Chem., 2010, available online 46

O

O

O

O

O OO

OH

methyl oleate

primary ozonide

+

(1)

(2)

Ionic Liquids selected:

[MeOct3N][Tf 2N]MW= 648.85 g/mol),

[MeOct3N][CF3COO]MW = 481.73 g/mol

Ozonolysis of methyl oleate in ionic liquids

COOHO

O

HOOC

RHR COO

*O

CH O

R

OCH *

R

n

O ORCH CHR

O

pelargonic acid monomethyl azelate

-+1 2

+

1 2

1 2

secundary ozonideperoxide oligomer

(3)

(4)

3 3

MW = 481.73 g/mol

[Hex3TetradecP][Cl]MW = 519 g/mol

COOH

CHO

COOMeHOOC

COOMeOHC

monomethyl azelatepelargonic acid

nonanal methyl 9-oxononanoate(1)

(2)

(3)

(4)

47

Ozone OxygenYield (%)

1 2 3 4

2h/20°C 5h/20°C 15 35 14 36

2h/20°C 5h/100°C 14 36 6 44

2h/20°C 5h/20°C 16 34 15 35

10

20

30

40

50

Yie

ld (%

)

Yield nonanal

Yield pelargonic acid

Yield methyl 9-oxononanoate

Yield monomethyl azelate

IL= [MeOct3N][Tf 2N]

(1)

(2)

(3)

(4)

Oxidative workup of ozonide in IL

Reaction conditions : 1 mmol MO, 1.5g IL, 1) O3 phase: 0.25h, 20 °C, 0.78 mmol O3/min, 1000 rpm; 2) O2 phase: 7h, 100 °C, 0.50 L O2/min, 500 rpm

→ Acid yield of 95 % ….

Product isolation and IL recuperation ?

2h/20°C 5h/100°C 4 46 2 48

0.25h/20°C 7h/100°C 3 47 2 480

10

0 100 200 300 400 500

Reaction time/min

48

Product separation applying solvent resistant nanofiltration

Polyimide based membranes

One step filtration!Rejection IL = 96 ± 2 %

Membrane RIL (%)Permeability (L/m2 h bar)

Membrane A1 25±3 10.3±3.0

Membrane A2 40±5 6.9±5.7

Membrane B2 81±1 0.1±0.025

Membrane B3 96±2 0.2±0.1 Rejection IL = 96 ± 2 %Permeability = 0.38 ±0.05 L/m2hbar

Membrane B3 96±2 0.2±0.1

Membrane B3 [a] 90±0 0.375±0.05

Membrane B3[b] 93±1 0.35±0.1

Membrane B3 [c] 86±5 0.5±0.075

p (N2) = 40 bar, 1000 RPM stirring,T = 20°C; 0.5gof [MOct3N][Tf 2N], 0.00333 mmol of methyl oleate,0.3 mmol of azelaic acid, 0.3 mmol of pelargonicacid, 7ml of 2-butanone.[a] 50°C. [b] 20 bar. [c]

MeOH.

49

Part C. New reactions in ionic liquids / Strategies for product isolation

1. Reactions with spontaneous product segregationhydrogenolysisalcohol oxidation

2. Ozonations in ionic liquidsincl. membrane separations

Leuven University

3. Renewables utilization in ionic liquids ����sorbitol from cellulosealkylglycosides from cellulose

50

Cellulose

• insoluble in most traditional solvents;

• soluble in some ionic liquids

in BMimCl

Cellulose valorization in IL

in BMimCl

(1-butyl-3-methylimidazolium chloride)

up to 25 wt. %

dissolved as individual chains

nature of the anion is critical

O

OHOHO

OH

O O

OHOH

OH

O** n

OHOH

OH

OOH

OHOHOCH2

O

H

O

O

OH

H2OOHOH

OH

O

O

Levoglucosan (LG)

Levulinic acid

HMF

?

Max. 50% in acid conditions

51

Approaches to reductive cellulose valorization in IL: cellulose dissolved in BMimCl

• Direct hydrogenolysis, using catalysts for acetal / ketal hydrogenolysis

(e.g. Rh/C + BF3)

• Using a homogeneous catalyst for hexose hydrogenolysis to (lower) polyols:

HRuCl(CO)(PPh3)3 , activated by KOH as a base JACS 1989, 111, 4131

Cellulose conversion in BMimCl (I)

co-catalyst,% of cellulose

product amount in catalyst

co-catalyst,

additivetime, h

% of cellulose

converted to dimers

and smaller molecules

product amount in

final mixture, %

HRuCl(CO)(PPh3)3 (0.01 g) KOH (0.0072 g) 96 20 10 (dimers)

78 (glucose)

2 (sorbitol)

6 (levoglucosan)

4 (HMF)

HRuCl(CO)(PPh3)3 (0.033 g) KOH (0.0017 g),

H2O (3 µL)

48 100 1 (dimers)

76 (glucose)

20 (other C6-sugars )

3 (sorbitol)

Reaction conditions: cellulose (0.05 g), solvent (1 g BMImCl), temperature (150 C), hydrogen pressure (3.5

MPa, measured at 25 C).

52

A literature example: cellulose hydrolysis by homogeneous acids in [bmim][Cl]

Only for acids with a sufficiently low pKa, significant accumulation of glucose from cellulose

Maximal yield:

~50 % of glucose

Vanoye, Seddon et al., Green Chem., 2009, 11, 390-653

The role of various catalysts & additivescatalyst co-catalyst,

additive

% of cellulose converted to

dimers and smaller molecules

product amount in

final mixture, %

0.5% Pt/C (0.033 g)

HRuCl(CO)(PPh3)3 (0.033 g)

KOH (0.0017 g),

H2O (3 µL)

100 51 (sorbitol)

49 (glucose)

0.5% Pt/C (0.033 g),

---

KOH (0.0017 g),

H2O (3 µL)

0.3 86 (glucose)

14 (levoglucosan)

HRuCl(CO)(PPh3)3 (0.033 g),

0.5% Pt/C (0.033 g)

---,

H2O (3 µL)

19 19 (glucose)

25 (other C6-sugars)

22 (sorbitol)

16 (C5-sugars)

4 (C5-alcohols)

11 (levoglucosan)

3 (C4-alcohols)

Reaction conditions: cellulose (0.05 g), solvent (1 g BMImCl), temperature (150 C), hydrogen pressure (3.5

MPa, measured at 25 C), reaction time (48 h)

Homogeneous Ru, KOH, and heterogeneous Pt are all needed ! 54

Combining Ru-complex with other heterogeneous metal catalystscatalyst % of cellulose converted to dimers and

smaller molecules

product amount in

final mixture, %

0.5% Pt/C (0.033 g),

HRuCl(CO)(PPh3)3 (0.033 g)

100 51 (sorbitol)

49 (glucose)

HRuCl(CO)(PPh3)3 (0.033 g),

5% Rh/C (0.0388)

100 26 (glucose)

74 (sorbitol)5% Rh/C (0.0388) 74 (sorbitol)

HRuCl(CO)(PPh3)3 (0.0388 g),

5% Pd/C (0.0443 g)

1.3 57 (hexoses)

15 (sorbitol)

8 (C5-sugars)

20(C5-alcohols)

8 (C4-alcohols)

Reaction conditions: cellulose (0.05 g), solvent (1 g BMImCl), co-catalysts (3 µL H2O, 0.0017 g KOH),

temperature (150 °C), hydrogen pressure (3.5 MPa, measured at 25 °C), reaction time (48 h)

55

Conclusions on cellulose hydrogenolysis

Heterogeneous metal catalyst (Pt/C, Rh/C)

• To effect the glucose hydrogenation;

Homogeneous Ru catalyst

• To transport H2 to the metal surface;

Indications:

glucose hydrogenation on Pt/C in BMimCl is very slow without Ru co-catalystglucose hydrogenation on Pt/C in BMimCl is very slow without Ru co-catalyst

H2 solubility data (5MPa): 0.044 mole/L in [BMIm][PF6]

129 mole/L in iPrOH

KOH base

To activate the homogeneous Ru catalyst.

Effective system, with up to 74 % sorbitol yield, but (too) complex

56

One-pot hydrolysis of cellulose and glucose alkylation in ionic liquids

• Cellulose hydrolysis in BMimCl proceeds under acid catalysis at 90-110°C,

but yield is limited to ~50%;

• Conditions for subsequent glucose alkylation:

Acid zeolite, 110 °C, 20-fold BuOH excess

→ 95 % yield alkylglycosides(Moreau et al., J. Catal. 185 (1999) 445)(Moreau et al., J. Catal. 185 (1999) 445)

One-Pot conversion ?

57

Glucose conversion: examples (I)• 0.25 g glucose

1.5 wt% H-Beta zeolite 5 mL n-butanol110 °C, 4 h

33 % yield butyl-glucofuranoside

65 % yield butyl-glucopyranoside65 % yield butyl-glucopyranoside

* A. Corma, S. Iborra, S. Miquel, J. Primo, J. Catal. 1996, 161, 713 – 719.58

Glucose conversion: examples (II)• 4.8 g glucose

6 wt% HY15 50 mL n-butanol110 °C, 4 h

15 % yield butyl-glucofuranoside

80 % yield butyl-glucopyranoside80 % yield butyl-glucopyranoside

* J.-F. Chapat, A. Finiels, J. Joffre, C. Moreau, J. Catal. 1999 185, 445 – 453.

59

Initial experiments with glucose.

# Solventn-Butanol,

mLCatalyst α-BGP β-BGP

1 - 1 0.01 g H-β zeolite 47 10

2 [b] 1 g BMImCl 0.3 0.005 g PTSA 31 26

3 - 1 0.01 g Amberlyst 15DRY

48 32

4 1 g BMImCl 0.3 0.01 g Amberlyst 14 124 1 g BMImCl 0.3 0.01 g Amberlyst 15DRY

14 12

[a] Reaction conditions: glucose (0.01 g), 90 °C (except entry 2), 4 h. [b] Reaction conducted at 80 °C.

60

Initial experiments with cellulose.

# Catalyst α-BGP β-BGP BGF GlucoseOther C6-

sugarsLG

1 0.01 g Hβ – zeolite 0 0 0 0 0 0

2 0,01 g MCM-41 0 0 0 0 0 02 0,01 g MCM-41 0 0 0 0 0 0

3 0.01 g Amberlyst 15DRY

29 16 5 10 0 7

[a] Reaction conditions: substrate (cellulose 0.05 g), reagent (0.3 mL n-butanol),110 °C (except entry 3), 24 h.

Amberlyst 15DRY is capable of cellulose hydrolysis

61

Time profile of reaction between cellulose (0.05 g) and n-butanol (0.3 mL) in

BMImCl (1 g) in the presence of Amberlyst 15DRY (0.01 g) at 110 °C

35

40

45

50glucose

α-BGP

β-BGP

BGF

0

5

10

15

20

25

30

0 4 8 12 16 20 24time (h)

conc

. (m

ol %

)

62

Pyrolysis of mixture of glucose and α-BGP in BMImCl (1 g) in the presence of Amberlyst 15DRY (0.01 g) at 110 °C

60

70

80

90

100

conc

. (m

ol %

)

glucose

α-BGP

levoglucosan

0

10

20

30

40

50

60

0 2 4 6 8 10

time (h)

conc

. (m

ol %

)

Glucose is being pyrolised faster than BGP63

Attempts to optimize conversion of cellulose.

# SolventCo-

catalystα-BGP β-BGP BGF Glucose LG

Total amount of butylated products

1 1 g BMImCl - 29 16 5 10 7 50

2[b] 1 g BMImCl 3 µL H2O

61 25 0 11 4 86

3[b] 1 g BMImCl - 52 30 3 9 6 85

4[c] 1 g BMImCl - 37 20 13 18 12 70

5[d] 1 g BMImCl - 33 16 12 27 12 61

6[e] 1 g BMImCl - 28 12 11 15 8 51

7[f] 1 g BMImCl - 24 10 9 18 9 43

[a] Reaction conditions: substrate (cellulose 0.05 g), reagent (0.3 mL n-butanol), catalyst (0.01 g Amberlyst 15DRY), 110 °C, 24 h. [b] After 4 h 1.2 mL of n-butanol were added into the reaction mixture. [c] The major fraction of Amberlyst 15DRY particles were removed after 4 h. [d] Ca. 70% of Amberlyst 15DRY particles were removed after 4 h.[e]The major fraction of Amberlyst 15DRY particles were removed after 2 h. [f] Ca. 70% of Amberlyst 15DRY particles were removed after 2 h.

Addition of extra n-butanol is helpful64

30

35glucose

α-OGP

β-OGP

OGF

Time profile of reaction between cellulose (0.05 g) and n-octanol (0.5 mL)

BMImCl (1 g) in the presence of Amberlyst 15DRY (0.01 g) at 110 °C

0

5

10

15

20

25

0 4 8 12 16 20 24

time (h)

con

c. (

mo

l. %

)

65

Transalkylation of α-BGP with n-octanol.

Entry Amberlyst 15DRY mass,

g

Yield of α-OGP,

%

Yield of β-OGP,

%

Yield of

OGF, %

Yield of glucose,

%

Yield of

BGF, %

Yield of

BGP, %

Yield of levoglucosa

n, %

Total yield of octylated

compounds, %

1 0.020 38 21 5 15 6 5 10 64

2 0.010 30 10 4 12 4 10 8 44

3 0.001 6 4 8 0 0 80 0 18

4 0 0 0 3 0 0 90 0 10Reaction conditions: α-BGP 0.05 g, 1 g BMImCl, 0.5 mL n-octanol, 110 °C, 24 h.

66

Run profile of reaction between cellulose (0.05 g), n-butanol (0.3mL) and subsequently n-dodecanol (two loads of 0.611 g, indicated by arrows) in

BMImCl (1 g) in the presence of Amberlyst 15DRY (0.01 g) at 110 ◦C.

Consecutive additions of n-dodecanol are indicated by arrows 67

Conclusions on alkylglucosides from cellulose

• Dissolution of cellulose in IL → efficient depolymerization and good reactivity

• Addition of acid catalyst → pyrolysis• Addition of acid catalyst → pyrolysis

• Good yields for butyl-glycosides and octyl-glycosides

Some amount of dodecyl-glycopyranoside was also synthesized through cross-alkylation

• Separation → supercritical antisolvent precipitation with carbon dioxide, nanofiltration

68

Igor A. Ignatyev, Pascal G. N. Mertens, Charlie Van Doorslaer,a Koen Binnemansb and Igor A. Ignatyev, Pascal G. N. Mertens, Charlie Van Doorslaer,a Koen Binnemansb and Dirk E. de Vos*

Received 8th June 2010, Accepted27th July 2010Green ChemistryDOI: 10.1039/c0gc00192a

Igor.Ignatyev@biw.kuleuven.be

Ignatiev.Igor@gmail.com

69