Chapter 1Chapter 1Chapter 1Chapter 1

Introduction and Literature ReviewIntroduction and Literature ReviewIntroduction and Literature ReviewIntroduction and Literature Review

Chapter 1

1

1.1 IONIC LIQUIDS: WHAT ARE THEY?

Ionic liquids (ILs) have been accepted as agents of green chemical revolution in

both the academia and the chemical industries. They have the potential to reduce

the use of hazardous and polluting organic solvents due to their unique

characteristics. The terms room temperature ionic liquid (RTILs), non-aqueous

ionic liquid, molten salt, liquid organic salt and fused salt have all been used to

describe these salts in the liquid phase.1 ILs are made up of positively and

negatively charged ions, whereas water and organic solvents (such as toluene and

dichloromethane) are made up solely of molecules. The structure of ILs is

similar to that of table salt (sodium chloride) which contains crystals made of

positive sodium ions and negative chlorine ions, not molecules. While, salts do

not melt below 800◦C, most of ILs remain liquid at room temperature. The

melting points of sodium chloride and lithium chloride are 801◦C and 614◦C,

respectively. Since these conventional molten salts exhibit high melting points,

their use as solvents is severely limited. However, RTILs are liquid generally up

to 200◦C, ILs have a wide liquidus ranges. The adopted upper melting

temperature limit for the classification as ionic liquid is 100◦C and higher

melting ion systems are generally referred as molten salts.2

Therefore, ILs are known as salts that are liquid at room temperature (that melt

below 100 degrees) in contrast to high-temperature molten salts. They have a

unique array of physico-chemical properties which make them suitable in

numerous applications in which conventional organic solvents are not

sufficiently effective or not applicable.

1.2 HISTORICAL BACKGROUND

ILs have been known for a long time, but their extensive use as solvents in chemical

processes for synthesis and catalysis has recently become very significant. Welton1

reported that ILs are not new and some of the ILs such as ethylammonium nitrate was

first described in 1914.3 The earliest IL in the literature was created intentionally in

1970s for nuclear warheads batteries4. During1940s, aluminum chloride-based molten

salts were utilized for electroplating at temperatures of 100°C. In the early 1970s,

Chapter 1

2

Wilkes tried to develop better batteries for nuclear warheads and space probes which

required molten salts to operate.4 These molten salts were hot enough to damage the

nearby materials. Therefore, the chemists searched for salts which remained liquid at

lower temperatures and eventually they identified one which was liquid at room

temperature. Wilkes and his colleagues continued to improve their ILs for use as battery

electrolytes and then a small community of researchers began to make ILs and test their

properties.5,6 In the late 1990s, ILs became one of the most promising chemicals as

solvents. The first ILs (such as organo-aluminate ILs) had limited range of applications

because they were unstable in air and water. Furthermore, these ILs were not inert

towards various organic compounds.7 Following the first reports on the synthesis and

applications of air stable ILs such as 1-n-butyl-3-methlyimidazolium tetrafluoroborate

([bmim]BF4) and 1- n-butyl-3-methlyimidazolium hexafluorophosphate ([bmim]PF6), the

number of air and water stable ILs has started to increase rapidly.7 Recently, researchers

have discovered that ILs are more than just green solvents and they have found several

applications such as replacement of volatile organic solvents, precursors for making new

materials, effective conductor of heat, support for enzyme-catalyzed reactions, host for a

variety of catalysts, agents for purification of gases, media for homogenous/

heterogeneous catalysis and biological reactions and reagents for removal of metal ions.4

Some of the basic physical properties of ILs such as density and viscosity are still being

evaluated by the researchers as the study of the ILs is still a relatively young field.8 It is

therefore evident that the amount of research on ILs and their specific applications is

increasing rapidly. As an example, though the cation 1-ethyl-3-methylimidazolium has

been the most widely studied until 2001, 1-3-dialkyl imidazolium salts are the most

investigated class of ILs in recent times. The future aim of research in ionic liquids

focuses towards their commercialization in order to use them as solvents, reagents,

catalysts and materials in large-scale chemical applications.

1.3 CLASSIFICATION OF IONIC LIQUIDS

Typical cations in ionic liquids are imidazolium, ammonium, pyridinium, pyrrolidinium,

phosphonium and sulfonium derivatives. The anions may be of inorganic or organic

origin. Common inorganic anions are halide, tetrachloroaluminate (also

tetrachloroferrate and tetrachloroindate), tetrafluoroborate, hexafluorophosphate and

Chapter 1

3

bis(trifluoromethylsulfonyl)imide and common organic anions are derivatives of

sulfate or sulfonate esters, trifluoroacetate, lactate, acetate or dicyanamide.9-11

Substituents (the R-group) on the cation are usually alkyl chains, but can contain

any of a variety of functional groups, such as fluoroalkyl, alkenyl, methoxy or

hydroxyl groups. Functionalized ILs are often designed for a particular use, e.g. for

specific reactions, extractions or separations and these ILs are then referred to as “task

specific ionic liquids” (TSILs).12 Table 1.1 shows the cations and anions organized

according to their relative acidity and basicity. Lewis basic and Lewis acidic families

of ionic liquids are expanding continually in terms of their discovery and utility.13,14

Table 1.1: Structures and nomenclature of the most common cations and anions

in ILs, and their acidis/ basic properties. 15

The relative acidity and basicity of the component ions imparts variety of physical

characteristics to the ionic liquids. A smart distinction can be gives as follows:

Chapter 1

4

1.3.1 Neutral Anions and Cations

Typical ionic liquid anions are those that can be described as neutral in the acid/ base

sense or very weakly basic; these exhibit only weak electrostatic interactions with the

cation and thus impart advantageously low melting points and viscosities. Included in this

class are anions such as PF6-, bis(trifluorometahnesulphonyl)imide (TFSI / Tf2N

-), BF4-,

methanesulfonate (mesylate), thiocyanate, tricyanomethide and p-toluenesulfonate

(tosylate). ILs formed from these anions typically exhibit good thermal and

electrochemical stability and thus, are often utilized as inert solvents in a wide range of

applications. 16-19

1.3.2 Acidic Cations and Anions

The simplest examples of slightly acidic ILs are those based on the protic ammonium,

pyrrolidinium and imidazolium ions, of which many are known. The well known

AlCl3 based ILs are Lewis acidic when they contain an excess of AlCl3.20-30

1.3.3 Basic Cations and Anions

There are a number of ionic liquid forming anions that can be called basic. These

include the lactate, formate, acetate (and carboxylates generally) and the dicyanamide

(dca) anion. The dicyanamides, in particular, have become readily available because

of their low viscosity. The basicity of these anions imparts different, advantageous

properties to the ILs, such as different solubilizing and catalytic properties.15 An

alternative to the design of ILs utilizing a basic anion is to incorporate a basic site into

the cation. This may afford more thermally stable ILs than those containing basic

anions, which frequently exhibit relatively low decomposition temperatures.13

1.3.4 Amphoteric Anions

There are a small number of ionic liquid anions that fall into the interesting class of

amphoteric anions, with the potential to both accept and donate protons depending on

the other substances present. The hydrogen sulfate (HSO4-) and dihydrogen phosphate

(H2PO4-) anions are simple examples of such anions.13

Chapter 1

5

1.4 PROPERTIES OF IONIC LIQUIDS, PHYSICAL AND CHEMICAL

Depending upon the application, properties of ionic liquids (whether physical or

chemical) can be tailored with the selection of suitable cationic and anionic

components. In this section an overview of the properties of ionic liquids ranging

from few physical and their common chemical behavior is given.

1.4.1 Melting point and liquidus range; Tm

Melting is said to occur when molecules or ions fall out of their crystal structure and

become disordered liquid. The two constituent of an ionic liquid- cation and its

corresponding anion, affect the melting point (Tm) of the former. In general, charge,

size, symmetry, intermolecular interaction and delocalization of charge are some of

the main factors that can influence the melting point.6,11,31-36 The melting point of ILs

is essential because it represents the lower limit of the liquidity and with thermal

stability it defines the interval of temperatures within which it is possible to use ILs as

solvents.37

Researchers have explained that ILs remain liquid at room temperature because their

ions do not pack well.38 Their low melting behavior is attributed to their chemical

composition. Combination of bulky and asymmetrical cations and evenly shaped

anions form a regular structure, lowering the lattice energy and hence the melting

point of the resulting ionic medium. In some cases, even the anions can be relatively

large and they can play a role in lowering the melting point.39

A comparative study here in Table 1.2 illustrates the trend in melting point of the

imidazolium ionic liquid system as affected by the size of anion. With increasing size

of the anion, the coulombic electrostatic interactions with the imidazolium cation in

the crystal lattice diminishes and melting point of the salt decreases. In combination

with a good charge delocalization, low solid-liquid phase transition temperatures can

be achieved. Melting point of a 1-ethyl-3-methyl imidazolium salt decrease from

87 °C to -14 °C in the order of Cl− > NO3− >BF4

− >CF3COO− (Table 1.2).5,6,16,40,41 The

melting temperature generally decreases with increasing anion radius except for anion

PF6−. This is because ILs with anions of PF6

− form strong hydrogen bonds due to

presence of fluorine atom and hence their melting points are comparatively higher.42

Chapter 1

6

Table 1.2: Effect of anion size on the melting temperature of imidazolium ILs.43

Alkyl chain length also has a significant influence on the melting point. As an

example, melting of the ionic liquid based on 1-alkyl-3-methyl imidazolium cations

decreases with alkyl-chain length up to n = 8-10. However, beyond this point, van der

Waals interactions between the hydrocarbon chains gain more importance. The

melting point of an ionic liquid starts to rise with increasing alkyl chain length and its

symmetry decreases.11,44 Moreover, as branching on the alkyl chain increases the

melting point also increases.

Methylation at C-2 increases the melting point of alkylimidazolium based ionic

liquids. As an example, the melting point of 1-ethyl-2-methyl imidazolium chloride is

181°C, which is much higher than that of 1-ethyl-3-methylimidazolium chloride

87.15°C. This implies that the effect of the van der Waals interaction via a methyl

group dominates over the electrostatic interaction via proton on C-2.45

1.4.2 Glass transition temperature Tg

The glass transition is another important physical parameter important to ILs.

The glass transition temperature (Tg) is defined as the temperature at which transition

happens from a solid crystalline state to an amorphous solid state. However, it should

Chapter 1

7

be noted that even crystalline solids may have some amorphous portion in them. Due

to this reason some ILs may have both- a glass transition temperature as well as a

melting temperature. In the case of most ILs, cooling from the liquid state leads to

glass formation at low temperatures as a result of the extremely unfavorable packing-

efficiency in the solid state. Usually, the glass transition temperature (Tg) is found to

be lower than -50°C46 and particularly in the range between -70°C and -90°C for

1- alkyl-3-methyl imidazolium salts.1

On the average, ionic liquids have a wide temperature range for the liquid state,

frequently found from-80 °C up to 300 °C. The melting point represents the lower

limit of the liquid range within which it is possible to use the salt as a liquid. The

upper limit is usually related to the thermal decomposition of ILs, as most of them are

non-volatile. Until now, the statement that ILs have no vapor pressure has not only

theoretically been refuted, in some cases distillation of ILs in vacuum is also

possible.47,48

1.4.3 Decomposition temperature Td

Thermal decomposition of an ionic liquid is strongly dependent on its structure. With

certain ions it is also dependent on the sample pan composition.33 Different from

organic solvents, many kinds of ILs can be kept in the liquid state above 400 °C and

this makes them have good dynamic properties and excellent catalytic activities.

Generally, the imidazolium cations tend to be thermally more stable than the tetra-

alkyl ammonium cations. High thermal stability is provided by certain kinds of anions

such as TFSI-. The relative anion stabilities follows the order; PF6- > TFSI- > CF3SO3

-

> BF4- >> I-, Br-, Cl-. The decomposition temperature (Td) is mainly influenced by the

strength of the incorporated heteroatom-carbon and heteroatom-hydrogen bond.49

High decomposition temperatures can be provided by ILs whose cations are obtained

by quaternization reaction using an alkylating agent and in special cases Td up to

450 °C can be obtained.50 In general, the temperature stability is higher when weakly

coordinating anions are used (Table 1.3).16,33,40,51,52

Chapter 1

8

Table 1.3: Influence of the anion on the decomposition temperature (Td) for 1-

ethyl-3-methyl imidazolium based ILs.51

1.4.4 Viscosity

ILs can be classified generally in terms of their Newtonian or in some cases

thixotropic characteristics.53 Their viscosities range from 10 mPas to 500 mPas at

ambient temperature,1 which is two or three orders of magnitude higher than

viscosities of traditional organic solvents.54 This is quite higher than viscosity of

water; 0.89 mPas. The high viscosities of ILs are therefore one of the major limiting

factors for their large-scale use. In most cases, viscosity is influenced by the tendency

of the constituents to form hydrogen bonds and by the strength of their van der Waals

interactions.16 The ability of hydrogen bonding is mostly affected by the anions

present. Within a series of imidazolium based ILs carrying the same cation, variation

of the anion clearly changes the viscosity in the general order Tf2N⎯ < BF4⎯< PF6

⎯<

halides. Furthermore, for ILs with the same anion, the trend of increasing viscosity

with increasing chain length of the alkyl substituent (by means of stronger van der

Waals interactions) has also been cited.11,16 Lengthening of alkyl chain or fluorination

can make the salt more viscous, due to an increase in van der Waals interactions and

hydrogen bonds.16 Similarly, methylation at C(2), but not at C(3), increases the

viscosity as it does for the melting point.

The viscosity of many ILs is strongly dependent on the temperature also. The

empirical equation 1.1, is also applicable in ionic liquid systems to describe the

Chapter 1

9

temperature dependence of the dynamic viscosity for unassociated liquid

electrolytes.16

η = A eε/ RT (1.1)

Temperature and also the presence of additives are important factors in influencing

the viscosity of ILs. The viscosity will decrease when the temperature is slightly

increased6,55,56 or little organic solvent55,56 is added to ILs.

1.4.5 Density

The densities of most of the ILs are higher than water except for pyrrolidinium

dicyanodiamide and guanidinium (where density ranges from 0.9gcm-3 to 0.97gcm-3).

Density of ILs decreases as the number of carbon atoms in the alkyl group and the

sum of carbon numbers for the quaternary ammonium ILs increases.42 It is interesting

to note that the density of 1-methylimidazolium ionic liquids decreases linearly with

increasing temperature but at a rate less than that for molecular organic solvents.40

1.4.6 Surface tension

Data available on the surface tension of ILs is very limited. Their liquid/air surface

tension values are somewhat higher than conventional solvents (e.g., hexane: 1.8 Pa

cm), but not so high as water (7.3 Pa cm).51 Dzyuba and Bartsch have reported the

influence of the 1-alkyl group on the surface tension of [Cnmim]PF6 and

[Cnmim]TFSI and have pointed out that the surface tension decreases with the

increase of the carbon number and a lower surface tension is found for TFSI− salt than

the corresponding PF6−.57

1.4.7 Purity; Anionic impurity

Impurities, such as water, halides, unreacted organic salts and organics, are usually

retained in ILs during synthesis or catalytic applications.58 These expected impurities

may influence the solvent properties53,59 and/or interfere with the catalyst or

biocatalyst.60

Chapter 1

10

It is therefore of utmost importance to assess the purity of the ILs. The Vollhard

method or an ion-selective electrode method can be used to measure chloride, and the

later method can be applied for the measurement of sodium also. Water can be found

to be present in ILs either due to ineffective drying after preparation or due to

absorption from the atmosphere due to the hygroscopic properties of the synthesized

ILs. However, even water immiscible ILs are known to absorb moisture from

atmosphere. Indeed, [C4mim]PF6 can absorb up to 0.16 mole fraction of water from

atmospheric air (measurement through Karl-Fischer titration).

Both water and chloride impurities can alter physical properties of ILs considerably.

The presence of contamination with chloride can increase the viscosity of the ILs,

whereas the presence of water, or other co-solvents, can reduce the viscosity. The

addition of co-solvents in general reduces the viscosity, with the effect being stronger

for co-solvents with higher dielectric constant. The structural changes affecting

majority of properties at an equimolar concentration of water and ionic liquid

indicates the possible formation of a hydrogen-bonded complex with water.53

1.4.8 Solvent properties of ILs

1.4.8.1 Polarity

Polarity behavior of any chemical helps in classifying it as a solvent. Under the

definition of polar solvent, i.e. a solvent having the ability to dissolve and stabilize

dipolar or charged solutes, ILs are highly polar solvents. But this cannot be strictly

concluded as ILs can be designed in a vast range. Ionic liquids can therefore, be

classified as dipolar, protic or aprotic solvents respectively. The solvent polarity for

experimental and theoretical studies is determined by the values of dielectric

constants, dipole moments and polarizabilities.1 However, a direct measurement of

the dielectric constant which requires a non-conducting medium is not available for

ionic liquids.

Attempts have been made to develop empirical solvent polarity scales for ILs as a

means of explaining differences in solvent-mediated reaction pathways, reaction yields,

synthesis product ratios, chromatographic retention, and extraction coefficients. Based

Chapter 1

11

on the comparison of the effects on the UV-visible spectra for sets of closely related

dyes, Abboud, Kamlet, and Taft evaluated some typical properties, dipolarity or

polarizability (π*), H-bond basicity (β), and H-bond acidity (α).61-63 Different

investigations of solvent-solute interactions in ILs using solvatochromic dyes have been

reported.61,62,64 Crowhurst et al.65 applied the Abboud-Kamlet-Taft method using three

solvatochromic dyes (Richardt’s66, N,N-diethyl-4-nitroaniline, and 4-aniline) to

determine the solvent parameters π*, β and α of imidazolium ILs (Table 1.4). The π*

values found by Crowhurst et al. for the investigated ILs indicated higher values of

dipolarity or polarizability than that of alkyl chain alcohols. Although differences

between the ILs are small, both the cation and the anion have been found to affect this

parameter. On the contrary, the H-bond basicity of the examined ILs covers a large

range, from a similar value to that of acetonitrile to lower β-values. The parameter β for

H-bond basicity is determined by the nature of the anion while H-bond acidity is

determined by the cation, (even if a smaller anion effect is there). In particular, it has

been suggested that α values are controlled by the ability of the cation to act as an H-

bond acceptor; a strong anion-cation interaction reduces the ability of the cation to

hydrogen bond with the substrate. The acidity of the investigated ILs is generally less

than those of water and most short-chain alcohols but greater than those of various

organic solvents.20 The polarity scale of several organic solvents including different

groups of ionic liquids is illustrated in Figure 1.1.43

The solvent properties of the ILs have also been investigated using chromatographic

techniques.67-72 The solvent properties of ILs i.e. their ability to act as a hydrogen-

bond donor or acceptor, have been measured by Anderson et al.73 GC retention times

of a range of probe solutes on a variety of columns using ILs as the stationary phases

were studied. The ILs were found to interact with solutes via high dipolar and

dispersion forces and also acted as strong hydrogen bond bases.

A different approach towards measurement of solvent polarity is based upon the

measurement of keto-enol equilibria (as this is known to be affected by the polarity of

the medium). This particular methodology, when applied to probe the polarity of ionic

liquids, indicated that [bmim]BF4, [bmim]PF6, and [bmim]NTf2 are more polar than

organic solvents such as methanol or acetonitrile.74

Chapter 1

12

Table 1.4: Kamlet-Taft parameters for few ILs.20

Ionic liquid ET a Π* α β

[bmim]BF4 0.670 1.047 0.627 0.376

[bmim]PF6 0.669 1.032 0.634 0.207

[bmim]OTf 0.656 1.006 0.625 0.464

[bmim]NTf2 0.644 0.984 0.617 0.243

[omim]PF6 0.633

Ethanol 0.650

aET = 28592/ (the wavelength maximum of the lowest energy π-π* absorption band of the zwitter ionic Richardt’s dyes).

Figure 1.1: Normalized solvent polarity scale for several organic solvents and different

groups of ionic liquids.75

In the case of ILs based on 1-alkyl-3-methyl imidazolium cations, the polarity is

influenced by the anion, for shorter alkyl chains, whereas for longer alkyl chains the

influence of the anion present is less. The polarity typically decreases in the order of

NO2⎯ >NO3

⎯ >BF4⎯ >Tf2N⎯ >PF6

⎯ and with anion size (more particular with the

effective charge density of the anion).76

Chapter 1

13

1.4.8.2 Miscibility behavior of ILs

The search for alternative solvents to meet the cleaner technology requirements is

always under exploration since the most widely used solvents are volatile and

damaging. ILs are solvents of choice for a wide range of substances; organic,

inorganic, organometallic compounds, bio-molecules and metal ions. Generally, they

are composed of poorly coordinating ions which makes them highly polar but non-

coordinating solvents.2

Most of the listed categories of compounds are sufficiently soluble in ILs towards

their performance in organic transformations. With regard to their general solvent

properties, it has been concluded (on the basis of the Abraham free energy

relationship) that ILs resemble polar organic solvents such as acetonitrile,

N-methylpyrrolidone, or methanol.77 A potential application of polar aprotic ILs is to

use them as a medium for solublizing biomolecules such as proteins and

carbohydrates (that are sparingly soluble in common organic media). However, it has

been found that even simple sugars do not dissolve to an appreciable degree in water-

miscible ionic liquids, such as [bmim]BF4. In contrast, [bmim]Cl can dissolve

massive amounts of cellulose.78 The ability of ionic liquids to act as solvents or to

dissolve complex compounds, such as sugars and proteins, mainly depends on the

ability of the salt to act as a hydrogen bond donor and/or acceptor and the degree of

localization of the charges on the anions.1,79 Charge distributions over anions, H-

bonding ability, polarity, dispersive interactions are the major factors that influence

the physical properties of ILs.80 As an example, imidazolium-based ILs are highly

ordered, hydrogen-bonded solvents and they have strong effects on chemical reactions

and processes.

Miscibility of ILs with water also varies unpredictably. [bmim]BF4 and

[bmim]MeSO4 are water-miscible, while [bmim]PF6 and [bmim]Tf2N are not. These

ionic liquids are of similar polarity on the Reichardt scale,75 and the coordination

strengths of the BF4- and PF6

- anions are also comparable.62 A measurement of the H-

bond accepting properties of such ionic liquids has revealed that BF4- and MeSO4

- are

better H-bond acceptors (β= 0.61 and 0.75, respectively) than PF6- (β= 0.50),81 which

could explain the difference in water miscibility. It must be taken into consideration

Chapter 1

14

that aqueous mixtures of ILs may not be homogeneous at molecular scale as, at this

level even water does not mix in methanol and is present as strings or clusters of

molecules.82 As discussed before, even water-immiscible ionic liquids can be

hygroscopic, as they can readily absorb water.53 IR spectroscopic analysis has

confirmed that water interacts mainly with the anion83 via the formation of double H-

bonds,84 at least in case where the cation is a weak hydrogen bond donor.

The miscibility behavior of ILs and organic solvents however is not well documented. A

relationship with the dielectric constant has been proposed, as lower alcohols and ketones,

dichloromethane and THF (ε = 7.58) mix with for example, [bmim]Tf2N, whereas

alkanes and ethers do not.16 Most of the ILs are immiscible with most of the organic

solvents and thereby provide a non-aqueous, polar alternative for two-phase systems.85

1.4.8.3 Volatility; Low vapor pressure

Due to their extremely low vapor pressure, ILs do not tend to give off vapors in

contrast to traditional organic solvents such as benzene, acetone, and toluene.

Kabo et al.86 have reported the vapor pressure of [bmim]PF6 at 298.15 K as

10Pa−11Pa. ILs can be introduced as green solvents because unlike the volatile

organic compounds (VOCs) they have negligible vapor pressure, are not explosive

and in certain cases may be feasibly recycled and used repeatedly. Moreover, these

non-evaporating ILs eliminate the hazardous exposure and air pollution problems.

Unlike conventional solvents ILs do not evaporate into atmosphere and their non-

volatility gives an opportunity to utilize them in high vacuum systems. In addition,

ILs are potentially good solvents for many chemical reactions in the cases where

distillation is not practical, or water insoluble or thermally sensitive products (e.g.

certain pharmaceutical compounds) are the components of a chemical reaction.2

Although, reported earlier ILs were not considered to be distilled due to their low

volatility, Earle et al.47 showed that many ILs, especially bistriflamide ILs can be

distilled at 200◦C–300◦C and low pressure without decomposition.

Thus, due to their stability, non-volatility, adjustable miscibility and polarity, ILs may

be used as ideal substitutes for conventional organic solvents.87

Chapter 1

15

1.5 SYNTHESIS METHODS OF IONIC LIQUIDS

ILs are ‘designer solvents’ since their specific properties can be tuned for a particular

need. A specific IL can be designed by choosing negatively charged small anions and

positively charged large cations and these specific ILs can be utilized to dissolve

certain chemicals or to extract them from a solution. The fine-tuning of the structure

provides tailor-designed properties so as to satisfy the requirements for a specific

application. The physical and chemical properties of ILs can be varied by changing

the alkyl chain length on the cation and the anion. As an example, Huddleston et al.88

concluded that density of ILs increases with a decrease in the alkyl chain length on

the cation and an increase in the molecular weight of the anion. It is estimated that by

combining various kinds of cation and anion structure, 1018 ILs can be designed.37,85

The most widely used cations are imidazolium, pyridinium, phosphonium and

ammonium ions. The overall properties of ILs result from the composite properties of

the cations and anions, where the anion controls the water miscibility and the cation

also has an influence on the hydrophobicity or hydrogen bonding ability of the ionic

liquid.89

1.5.1 Anion

ILs with varied properties can be obtained by introducing different anions. IL anions

can be of two types: fluorous anions such as PF6−, BF4

−, CF3SO3−, (CF3SO3)2N

− and

non-fluorous anions such as AlCl4−. Anions most commonly encountered in an IL are;

chloride, nitrate, acetate, hexafluorophosphate and tetrafluoroborate.90 However, in

designing ILs, fluorous anions are usually opted because of the distinct properties

they impart. As an example, as already discussed, IL with 1-n-butyl-3-

methylimidazolium cation and PF6- anion is water-immiscible, whereas IL with same

cation and BF4− anion is water soluble. This exemplifies the ‘designer solvent’

property of ILs, i.e. by changing the anion the density, hydrophobicity, viscosity and

solvation properties of the IL system can be altered.8 Although PF6- and BF4

− are the

two anion types that are utilized in most of IL applications, they suffer from a serious

Chapter 1

16

disadvantage. These anions undergo decomposition when heated in the presence of

water and liberate HF. Following the discovery of this phenomenon, fluorous anions

containing C-F bond which is inert to hydrolysis were started to be used.

Consequently, ILs bearing CF3SO3− and (CF3SO3)2N

− anions in which the fluorine is

bonded to carbon have been produced.91 However, fluorinated anions tend to be

expensive and toxic to the environment. Hence, alkylsulfate anions derived from

inexpensive bulk chemicals have been found as the most popular non-fluorous anions

due to their non-toxic and biodegradable structures.91

1.5.2 Cations

The preferable cation for any ionic liquid is one having a bulky structure with low

symmetry. Most of the ILs currently in research are based on ammonium, sulfonium,

phosphonium, imidazolium, pyridinium, picolinium, pyrrolidinium, thiazolium,

oxazolium and pyrazolium cations.2 Properties of ILs, such as melting temperature,

density, viscosity etc. are affected differently with variation in size, symmetry and

alkyl chains attached to cation (as already discussed in Section 1.4). Not only this,

different ILs can be designed by introducing a suitable functionality into the cation

leading to the formation of third generation ILs-Task specific ILs.12 An essential

target to chemists involved in organic transformations and total synthesis is tuning the

stereochemistry of the product. In this respect, chiral ILs have been suitably designed

to carry out the work of asymmetric synthesis.92

1.5.3 Synthesis

The synthesis of ILs generally proceeds in two steps: formation of the cation followed

by anion exchange (metathesis). Typical synthetic pathways for the preparation of ILs

are shown in Figure 1.2, where the preparation of imidazolium based ILs is taken as

an example.

The cation formation step, most often described as a quaternization reaction, imparts

ionic nature to the compound. The starting material, imidazolium (or amine,

Chapter 1

17

pyrimidine, etc.), is alkylated with an appropriate alkyl halide (RX) and in halogen

based ILs, this is the only step which is required. However, quaternization with alkyl

halides sometimes may leave traces of halide ion in the ionic liquid. Not always, but

halide ions can also interfere with metal catalysts, can cause corrosion problems in

chemical plants and interfere with measurements of physical property of ILs.93 As an

alternative, ILs can be synthesized via a “halogen- free” route, where an alkyl

alkylsulfonate, usually alkyl methylsulfonate (mesylate)94 or alkyl toluenesulfonate

(tosylate)95, is used for the quaternization reaction. The quaternization reaction can

also proceed by protonation with a Brønsted acid.

The anion exchange reactions can be brought about in two possible ways: a halide salt

can be treated with a Lewis acid to form a Lewis acidic ionic liquid, or an exchange

reaction can be carried out by anion metathesis.11 Typical Lewis acids that can be

used in this context are AlCl3, BCl3, CuCl2, FeCl2, or SnCl2.

Figure 1.2: Synthesis routes for the preparation of methylimidazolium based ionic liquids.11

Chapter 1

18

The beginning of IL preparation dates back to 1914, where ethylammonium nitrate

([EtNH3]NO3, mp 13°C-14°C) was prepared by neutralization of ethylamine with

concentrated nitric acid. The discovery did not attract much scientific interest and

these new materials went largely unrecognized till the 1970s when organic

chloroaluminates (first- generation ILs, Figure 1.3) were investigated. In the 1990s,

Wilkes and Zaworotko reported the preparation of air- and moisture-stable ILs

(second- generation ILs, Figure 1.3) using new combinations of cations and anions.

Since then, a wide range of ILs have been developed including TSILs (third-

generation ILs, Figure 1.3), which were introduced by Davis12 in 2004.9,10

Figure 1.3: The three generations of ionic liquids.10

Below is thus summarized, generation vise synthesis of ILs; ranging from ammonium

ILs, non- functionalized ILs, functionalized task specific ILs (TSILs) and chiral ILs.

1.5.3.1 Ammonium cation based ILs

The aliphatic quaternary ammonium (AQA) cation is a useful cationic component of

room temperature ILs (Figure 1.4), since the salts containing AQA cations and

appropriate oxidation resistant anions such as ClO4-, BF4

- or PF6- are

electrochemically stable and may be used as a supporting electrolyte. The asymmetric

amide anion (CF3SO2-N-COCF3)- has an excellent ability to lower both the melting

points and viscosities of room temperature ionic liquids, combining with the small

aliphatic cations.96

Chapter 1

19

Figure 1.4: AQA cations used in ILs97

There is, however, a limitation on the reduction of the viscosity of the AQA-based

room temperature ionic liquids, compared with the imidazolium systems as the

molecular weight of the AQA cations cannot be reduced to below a threshold value.96

1.5.3.2 Non-functionalized ILs

As already discussed, room temperature ionic liquids are prepared by direct

quarternisation of the appropriate amines or phosphines.98 Dialkylimidazolium and

alkylpyridinium cation-based ionic liquids have been easily prepared by alkylation of the

commercially available N-methylimidazole or pyridine with an alkyl halide to give the

corresponding 1-alkyl-3-methylimidazolium or 1-alkylpyridinium halide. Different

anions have subsequently been introduced by anion exchange (metathesis), although, due

to their non-volatile nature, they cannot be purified by distillation. Purification is

therefore, usually carried out by dissolving the ionic liquid in acetonitrile or

tetrahydrofuran (THF), treating it with activated charcoal for more than 24 h and finally,

removing the solvent in vacuuo.

A more recent method involves the microwave-assisted solvent-less synthesis of

imidazolium ionic liquids.99 The microwave heating reduces the reaction time from

several hours to minutes and avoids the use of a large excess of alkyl halides/ organic

solvents as the reaction medium. Dialkylimidazolium tetrachloroaluminates are

Chapter 1

20

prepared in a few minutes by the reaction of the appropriate N,N´-dialkylimidazolium

chloride and aluminium chloride under microwave irradiation.100 A new series of salts

based on the dicyanamide anion (dca), most of which are liquids at room temperature,

have been synthesized (Figure 1.5). These ILs have potential donor characteristics, as

the anion is a powerful ligand, and possess a lower viscosity.101

Figure 1.5: Dicyanamide anion based ionic liquids.101

1.5.3.3 Functionalised ILs; TSILs (Task Specific Ionic Liquids)

These have been described as a class of ILs, which incorporates functional groups

designed to impart to them particular properties or reactivities. Two basic rationales

have been given by Davis12 for the inclusion of functionality into an IL. First, the

inclusion of the functional group will undouubtedly alter the solvent parameters of an

IL relative to an analog bearing a simple hydrocarbon appendage.102 These

parameters-dipolarity, H-bond acidity and basicity, polarizability, etc. are the

attributes which make any chemical a good or poor solvent for a given solute.103 A

second rationale for a functional group being incorporated into an IL is to make the

salt with a capacity to covalently bind to or catalytically activate a dissolved substrate.

This application also parallels with the solid support catalysis using ILs. Moreover,

Scammells et al. have shown that the incorporation of certain functional groups

(especially esters) increases the rate of breakdown of an IL in the environment (a

factor of considerable practical importance).104,105

The conventional method (Figure 1.6) to synthesize TSILs involves displacement of

halide from a functionalized organic compound by a parent imidazole, phosphine etc.

in the quaternization step. This is followed by usual anion exchange step to yield the

desired task specific ionic liquid.12

Chapter 1

21

Figure 1.6: Conventional method for the synthesis of TSILs 12

Michael reaction has also been cited as a complimentary method for synthesis TSIL

(Figure 1.7).106 In this approach, the imidazole or other nucleophile of interest is

protonated using the acid form of the anion which will eventually be incorporated into

the IL, e.g., HPF6 for PF6-. To this salt is added the desired Michael acceptor, which

inserts into the N–H (or element–H) bond. The approach is broadly effective, giving

TSIL in good yields. Moreover, the procedure eliminates the need for an anion

metathesis step and provides an IL free of halide. The latter is an important factor if

the IL is to be used with a transition metal catalyst. The only apparent drawback

however, is the limited thermal stability of the cations, which at moderately elevated

temperatures can undergo a retro-Michael reaction. Various other methods have also

been cited by Davis, including the works from other research groups for the

incorporation of functionality into an IL.12

Figure 1.7: Michael reaction for synthesis of TSILs.106

Chapter 1

22

As far as applications of TSILs are concerned, by virtue of their incorporated

functionalities, these unique salts can act not only as solvents but also as catalysts and

reagents in an array of synthetic, separation and electrochemical applications.

1.5.3.4 Chiral ILs (CILs)

Chiral discrimination can be accomplished by using wide variety of chiral ionic liquids.

Although, CILs are at a premature phase of development, they have already found

promising applications as solvents for chiral separation techniques107, asymmetric

synthesis,108-112 stereoselective polymerization,113-115 chromatography,116,117 liquid

crystals118,119 and as NMR shift reagents.107,120-123

The CILs are supposed to meet the criteria of easy preparation by direct synthesis in

enantiopure form and have low melting points, good chemical stability towards water

and common organic substrates together with relatively low viscosity and good

thermal stability. Preparation and applications of CILs have been compiled by

Chauhan et.al.97

1.6 CHARACTERIZATION OF IONIC LIQUIDS

Characterization of the chemical properties of ILs is desired to gain a better

understanding of their fundamental characteristics. These properties on comparison

with those of conventional solvents allow determination of unique characteristics of

ILs. Viscosity and density allow for an understanding of bulk properties of the system

while several other internal properties can also been investigated.51,54,124,125 The effect

of constituent cation and anion of an IL over properties like density, viscosity, surface

tension, melting temperature and solvent properties have already been discussed.

However, a careful study involving conductivity measurements, thermal analysis,

measurement of decomposition temperature, structural analysis and toxicology studies

need to be done on these systems.

Electrochemical analysis of ILs have shown that the conductivity (and related

impedance) and of diffusion coefficients can be helpful in understanding the transport

properties and solvent-solute interactions within the ILs. Examination of imidazolium

Chapter 1

23

based ILs has shown that they exhibit low electrical resistance values.126 This should

be expected due to the charged nature of the ions and the corresponding high

concentration of such charges within a pure ionic liquid.

Thermochemical analysis of ILs such as phase equilibrium studies 127 have provided

an insight into the stability and solubility of ionic liquids and their interactions with

their surroundings. Since ILs consist of charged species, it would be expected that

lattice formation or similar structuring that may be present within these liquids can

directly affect their characteristics such as melting point. As already discussed in

Section 1.4.1, melting temperature is therefore a critical parameter, as the practical

use of ILs depends on the temperature range in which they remain in a liquid form.

Differential scanning calorimetry (DSC) has allowed for the determination of ionic

liquid melting, crystallization and glass transition (Tg) points and can help in

rationalizing the relationship between ionic liquid structuring and physical

characteristics.42 In general it has been found that increasing ion size (producing

weaker coulombic interactions in the crystal lattice) can significantly change the

melting point of ionic liquids. Moreover, with increasing side chain lengths, the

resulting weak van der Waals interactions can reduce the stronger hydrogen bonds

present in the system.11

Thermogravimetric analysis (TGA), coupled with DSC data, allows for examination

of decomposition temperatures, determination of limits of practical use and the overall

stability of ILs.128,129 Studies have identified that in certain cases perfluorination of

the anions (with stable C-F bonds such as those in NTf2-) can also enhance the

thermal stability of ILs (an important factor for their implementation in batteries). 130

Spectroscopic methods of analysis have been employed to probe the structure of ILs.

Techniques such as infrared (IR) and Nuclear Magnetic Resonance (NMR)

spectroscopy have allowed for diffusional131 and structural analysis132 of ILs, which

further help in understanding solvent-solvent interactions and their effects upon the

transport properties of the liquids. Mass spectrometry has allowed for more detailed

investigation of decomposition fragments. The pattern of such processes has enabled

the determination of physical properties such as enthalpy of vaporization133

Chapter 1

24

(a property that is related to the thermal stability of the liquids). In addition,

immobilization in HPLC stationary phases facilitates the investigation of ion

exchange properties of ILs and more specific interactions such as those with aromatic

compounds.134

Though not many studies have been done, ILs have been found to exhibit

considerable levels of toxicity.135-137 It has been reportedly found that phosphonium

based ILs can be labeled as corrosive in addition to irritating. Recent studies have also

shown that the length of alkyl chain (particularly imidazolium cations) can have a

direct and substantial impact upon the toxicity of ILs.138 However, biologically

compatible inert ions can serve as promising alternative to current ILs (which have

considerable levels of toxicity). Tao et al. have reported the synthesis of amino acid

based ILs with biodegradable characteristics.139 In addition to this, other bio-

compatible molecules such as the sugar based anions, succinate and lactate, can also

be used for the formation of ILs with much lower toxicity.140

1.7 MAJOR APPLICATIONS OF ILs

The outstanding physicochemical properties of ILs, especially room temperature ionic

liquids (RTILs), render them excellent candidates for a broad range of

applications.141-145 At the current level of development, ILs can even replace

conventional organic solvents in numerous different applications.9 ILs have already

been used as catalyst,146,147 reagents148 or solvents149,150 in several chemical reactions.

Furthermore, ILs can be used in separation processes151,152 and as electrolyte materials

in catalytic processes.153,154 Great efforts have been made in utilizing ILs as solvents

for biopolymers. Especially cellulose (the most abundant natural polymer in nature)

can be dissolved in rather high concentrations (up to 25 wt%) in ILs (which is not

possible in conventional organic solvents).78 The most efficient solubility can be

obtained when imidazolium based ionic liquids with chloride or acetate anions are

used, e.g. 1-ethyl-3-methyl imidazolium acetate or 1-n-butyl-3-methyl imidazolium

chloride. These anions are non-hydrated and can disrupt and break the intramolecular

hydrogen bonds of the cellulose network without derivatization.78,155,156 Beside the

usage of ILs as solvents for organic reactions, their applications as electrolytes in

Chapter 1

25

lithium batteries,157,158 in electroplating processes,159 and solar cells160-163 reflects their

applicability in electrochemistry. Remarkable are also the investigations of ILs with

regard to their advantages in formulation technology, in colloid science and in

tribology during the last years. ILs can also be utilized as additives in paints (for

improved finish and drying processes),164 as templates in nanotechnology165-172 or as

innovative lubricants for steel on aluminium applications.173

Interestingly, while on one hand ILs are known to pose a threat to nature, their

inherent cytotoxicity may have the potential for beneficial use in certain cases.

Current antifouling coatings, typically containing organic derivatives of heavy metals

such as tributyltin, have been found to leech from these coatings over time into the

environment. Ionic liquids have been successfully immobilized in polymers and found

to be sufficiently trapped so as to prevent leaching. The toxic nature of ILs can inhibit

growth, as desired, upon the polymer surface and so could potentially be used as

durable thin film coatings for filters or equipment exposed to potential bio-fouling

agents.174 An overview of the diversity of IL applications is given in Figure 1.8.

Figure 1.8: Major applications of ILs43

Chapter 1

26

1.8 ILs IN ORGANIC TRANSFORMATIONS

There has been a continuous and sustained research focusing on the use of ILs in

organic reactions and significant improvement in terms of products yields, reaction

times, reaction work-up have been obtained. However, the role of ILs in organic

transformation is still not very clear. Some authors have suggested that ILs can act as

an organocatalyst.175,176 One of the promising approach to organocatalysis is proposed

via hydrogen-bonding interactions and the results obtained with certain ILs have

confirmed this statement. On the other hand, Welton1,177 has studied catalytic

reactions in ionic liquids and has postulated that a potentially more powerful way in

which an IL can be used in catalysis can be a combination of both solvent and

catalyst. It is based on this postulate that whenever changing a solvent leads to an

accelerated reaction, the new solvent can be argued to behave like a catalyst. This is

simply because the reaction rate can be enhanced with the solvent remaining

unchanged in the process.

1.8.1 ILs as Solvents

In Section 1.4.8, the determination of solvent polarity parameters for ILs using

solvatochromic dyes, chromatographic techniques and the ability of ILs to affect the

keto-enol equilibria had been discussed. However, it turns out that ‘polarity’ or the

‘solvent strength’ alone can be insufficient in explaining the variation in experimental

results in many solvent-mediated processes. A reasonable postulate that has been

proposed by Bonacorso et al. as a general ionic liquid effect is that the accelerated

reaction rates can be a result of the decrease of activation energy of the slow step.20

ILs have been expected as a solvent media for the stabilization of highly polar or

charged intermediates, such as carbocations, carbanions and activated complexes.178

The influence of solvents on rate constants has been explained in terms of transition-

state theory. Solvents can thus help in modifying the Gibbs energy of activation (as

well as the corresponding activation enthalpies, activation entropies, and activation

volumes) by differential solvation of the reactants and the activated complex. The

effect of solvent on reactions has been investigated by Hughes and Ingold. They used

a simple qualitative solvation model considering only pure electrostatic interactions

Chapter 1

27

between ions or dipolar molecules and solvent molecules in the initial and transition

states179 and postulated that a change to a more polar solvent will increase or decrease

the rate of the reaction, depending on whether the activated reaction complex is more

or less dipolar than the initial reactants (Figure 1.9). In this respect, the term “solvent

polarity” has been used synonymously with the power to solvate solute charges.

Solvent polarity is thus assumed to increase with the dipole moment of the solvent

molecules and to decrease with the increased thickness of shielding of the dipole

charges.

Figure 1.9: Schematic Gibbs energy diagram for a general nucleophilic addition to

carbonyl carbon: (a) non-polar solvents; (b) polar solvents.20

Finally it is assumed that ILs as solvents can stop the use of volatile organic compounds

(VOCs) in pharmaceutical and petrochemical industries. The use of VOCs can be

assessed using a factor that measures process by-products as a proportion of production

on the mass basis - ‘Sheldon E- factor’. Researchers have analyzed that E-factor is

between 25 to 100 for pharmaceuticals industries with a production of 10 t/year to 103

t/year although oil refining industries with a production of 106 t/year to 108 t/year have an

E-factor of 0.1.31 These values suggest that pharmaceuticals industries use inefficient and

dirty processes although on smaller scale as compared to the oil refining industries.

Environmentally friendly ILs can presumably replace the hazardous VOCs in a large

scale context so as to reduce the E-factors.

Chapter 1

28

Since, ILs are able to dissolve a variety of solutes, they can be used instead of

traditional solvents in liquid–liquid extractions where hydrophobic molecules such as

simple benzene derivatives will partition to the IL phase. Huddleston et al.180-182

showed that [bmim]PF6 could be used to extract aromatic compounds from water.

Selvan et al.183 have used ILs for the extraction of aromatics from aromatic/ alkane

mixtures, whereas Letcher et al.184 have used ILs for the extraction of alcohols from

alcohol/ alkane mixtures. Moreover, binary temperature–composition curves of ILs

with alcohols, alkanes, aromatics and water; ternary temperature–composition curves

of ILs with alcohols and water; solubilities of some organics and water in ILs have all

been investigated by various groups so as to completely understand the solvent

properties of ILs.185-187

1.8.2 ILs as Catalyst

ILs can play an active role in chemical reactions and catalysis. Some of the examples

where ILs have been utilized are: reactions of aromatic rings, clean polymerization,188

Friedel Crafts alkylation,189 reduction of aromatic rings,190 carbonylation,191

halogenation,192 oxidation,193 nitration194 and sulfonation reactions.195 ILs can be

utilized as:

• Solvents/ co-catalyst/ catalyst activator for transition metal catalysis.

• Immobilization of charged cationic transition metal catalysis in ionic liquid

phase without need for special ligands178

• Immobilization of ionic liquid over a solid support

• In situ catalysis directly in ionic liquid rather than aqueous catalysis followed by

extraction of products from solution (this process eliminates washing steps,

minimizes losses of catalysis and enhances purity of the products).189

1.8.2.1 Ionic liquid as reaction media: Co-catalyst/ Catalyst activator

ILs can act as reaction media in both homogenous and heterogeneous systems. They

offer the advantages of both homogenous and heterogeneous catalysts with their two

main characteristics: A selected ionic liquid may be immiscible with the reactants and

products, but on the other hand the ionic liquid may be able to dissolve the catalysts.

Chapter 1

29

ILs therefore, combine the advantages of a solid for immobilizing the catalyst/ and the

advantages of a liquid for allowing the catalyst to move freely.196 The ionic liquids

have been shown to be superior solvents, with an enhancement of catalyst activity and

stability for transition-metal catalyzed reactions, in comparison to water and common

organic solvents, especially when ionic complexes of transition metals are used as the

catalysts.97 Brennecke and Maginn8 have indicated that the ionic nature of the ionic

liquid can give an opportunity to control reaction chemistry, either by participating in

the reaction or by stabilizing the highly polar or ionic transition states. Holbrey and

Seddon191 have described many of the catalytic processes which use low temperature

ILs as reaction media and have indicated that the classical transition metal catalyzed

hydrogenation, hydroformylation, isomerization, dimerization and coupling reactions

can be performed in IL solvents. In their review, they have concluded that ILs may be

used as effective solvents and catalysts for clean chemical reactions instead of the

volatile organic solvents.

In general it can be said that the reaction rates and selectivities are as good or better in ILs

than in conventional organic solvents. The catalytic hydrogenation of cyclohexene using

rhodium-based homogenous catalysts197 and hydrogenation of olefins using ruthenium

and cobalt-based homogenous catalyst198 in various ILs have been studied and the results

indicate that there is a certain increase in the reaction rates and selectivity compared to the

other normal liquid solvents. Lagrost et al. have shown that the diffusion coefficient of

the organic compounds are about 100 times smaller than those in conventional media as

expected from the lower viscosity of RTILs. The positive results of this study

demonstrated that ILs can be used as a new media for organic electrochemistry.199

ILs can also be employed as biological reaction media due to the stability of enzymes in

these liquids.200-203 Yet another important attribute of ILs in these reactions is their ability

to dissolve a variety of bio-molecules or substrates such as carbohydrates, amino acids,

organic acids such as lactic acids and in certain cases cellulose. According to Swatloski et

al.78 ILs incorporating anions which are strong hydrogen bond acceptors are most

effective solvents for cellulose, whereas ILs containing non coordinating anions

(including PF6− and BF4

−) are not that effective. Pfruender et al.204 tested the water

immiscible ILs-[bmim]PF6, [bmim]Tf2N and [oma]Tf2N (methyl-trioctylammonium

Chapter 1

30

trifluoromethanesulfonylimide) for their bio-compatibility towards Escherichia coli and

Saccharomyces cerevisiae. Results of this study indicated that these water immiscible ILs

did not damage the microbial cells and could be used as biocompatible solvents for

microbial bio-transformations as an alternative to toxic organic solvents.

1.8.2.2 Functional ILs and TSILs as catalyst; Catalysis in-situ.

Recently, ILs have been prepared so that one of the ions could serve as a catalyst for

the reaction.205,206 Functionalized ionic liquids that are able to act as catalysts

(particularly imidazolium salts containing anionic selenium species, SeO3Me-) have

been prepared.207 These salts have been used as selenium catalysts for the oxidative

carbonylation of anilines. Similarly, ILs bearing acid counter-anions (HSO4- and

H2PO4-) have been used as catalyst in recyclable reaction media for esterification

reactions.208 Similar results have also been obtained using zwitter-ionic ILs bearing a

pendant sulfonate group (which can be converted into corresponding Brønsted acid

ILs) by reaction with an equimolar amount of an acid that has a sufficiently low pKa

(TsOH, TfOH).209 ILs, containing the SO3H as a functionality, have recently been

employed in the oligomerization of various alkenes to produce branched alkene

derivatives with high conversions and excellent selectivity.210

Protonated ILs have been synthesized by direct neutralization of alkylimidazoles,

imidazoles, and other amines with acids and their physical properties (thermal stability,

conductance, viscosity) are currently under investigation. Brønsted basic ILs have also

been described as catalysts for organic reactions. As an example, Ranu and Banerjee

have demostrated the use of a tailor-made, task-specific, and stable ionic liquid

[bmim]OH as basic catalyst for Michael addition.211 On the other hand, the asymmetric

synthesis of ILs is still at a preliminary stage. Chiral ILs, for example, have been

synthesized and their use in asymmetric synthesis is under investigation.45,212-214

1.8.2.3 Immobilized ILs for catalysis

Immobilization of ILs is important as it utilizes only small amount of catalyst, which

could be easily recycled. A typical process for support or immobilization of ionic liquid

catalysts has been reported recently,215 in which the ionic liquid fragment (such as

dialkylimidazolium cation) was covalently anchored to the surface of silicon dioxide

Chapter 1

31

where this chemical bonding could limit the degree of freedom of the dialkylimidazolium

cation and even change the physicochemical properties of the ionic liquid. In another

method, immobilization of the ionic liquid has been proposed by dipping the porous

silicon dioxide in the mixture of ionic liquid containing the catalysts216 and in this case the

obvious leaching of the ionic liquid could not be avoided.

Alternative approaches that have been in practice to facilitate the catalyst re-use (and in

the context of continuous flow processes) is supported ionic liquid phase (SILP)

catalysis and this has been quite extensively studied.217,218 The general concept involves

the immobilization of imidazolium (together with other ionic fragments) onto solid

supports using appropriate functional groups attached to the cation and a charged

catalyst is then supposed to reside within the ionic matrix. The concept is illustrated in

Figure 1.10 for the racemic epoxidation of olefins using a peroxotungstenate catalyst,

supported on IL modified silica.219 The solid support was reacted with 1-octyl-3-

(3-triethoxysilylpropyl)-4,5-dihydroimidazolium, affording a SiO2 surface on which the

IL was covalently bound. This heterogeneous catalyst was used to successfully

epoxidise olefins using H2O2 as an oxidant and the reaction rates were comparable to

those observed under homogeneous conditions.

Figure 1.10: A tungstenate catalyst immobilized on IL modified silica.220

ILs have further proven to be excellent solvents to both immobilize and stabilize

nanoparticle catalysts. Nanoparticles were first identified in ILs as species formed

Chapter 1

32

during Heck reactions using Pd(II) compounds as catalyst precursors.221 Dupont et al.

reported the controlled preparation of transition metal nanoparticles in ILs by

reduction of the metal complex with molecular hydrogen in the absence of stabilizers

and demonstrated their application in hydrogenation and C-C coupling reactions.222,223

It is believed that both electrostatic and coordination effects of imidazolium cations

can contribute to nanoparticle stabilization by ILs.224 However, particularly more

forcing reaction conditions may nevertheless require the presence of additional

stabilizers to avoid aggregation of the nanoparticles in the ionic liquid. As an

example, PVP (poly-N-vinyl-2-pyrrolidone) has been used for nanoparticles synthesis

in ILs.225 In addition, thiol-functionalized ionic liquids226,227 and ionic liquid-like

copolymers228 have been developed to stabilize IL soluble nanoparticles. It has also

been demonstrated that nanoparticles stabilized by an IL polymer can be efficiently

transferred between phases via anion exchange229 and this could have important

applications in catalysis with respect to product separation.

1.8.2.4 Role of ILs in organic transformations

Based on the above discussion, it is clear that not all the ILs work in a similar manner

for a given organic transformation.37,230 However, the ILs can be tailor made for a

given reaction with ideal combination of cation and anion. Taking a view over the

most commonly encountered reactions in ILs (i.e. of SN2 type) a plausible explanation

has been proposed on the basis of Hughes-Ingold approach. In case of reactions of

highly associating anions (such as halides) reaction rates are greater in ILs composed

of the least coordinating cations (poor hydrogen bond acids) and the rate of the

reaction is affected by H-bonding ability and ion pairing property of the ionic liquid.

The relative rates of reaction can be therefore, compared. The H-bonding ability and

ion pairing property of ILs have been also used to explain the increase of reactivity

and selectivity in eletrophilic additions. It has been proposed that ILs can affect the

lifetime of reaction intermediates, affecting their stability or modifying the

nucleophilicity of the attacking anion. Furthermore, it can also affect the syn/anti ratio

by decreasing the rate of isomerization of the ionic intermediates through rotation

around the C-C bond.20

In electron transfer reactions, the enhancement of reactivity has been attributed to the

effect of cation-anion association and the presence of cavities in the ILs. It has been

Chapter 1

33

suggested that the highly ordered structure of these salts may contain voids and these

voids may be able to accommodate small solute molecules. Thus, the presence of

voids and the ability of small molecules to move within them have also been proposed

recently to explain the reactivity of hydrogen radical (H•) atoms with aromatic solutes

in ILs.231-233

Variety of catalytic reactions have been studied in ILs145,177 and ILs have shown

significant advantages over conventional solvents (especially in the case of

homogeneously catalyzed reactions).31 In these cases, the ionic liquid can be used in

“biphasic catalysis” or the catalyst can be entrapped or “immobilized” allowing

extraction or distillation of the organic product and the ionic liquid/catalyst system

can be reused. However, in order to achieve sufficient solubility of the metal complex,

a solvent of higher polarity is required and this may compete with the substrate for the

coordination sites at the catalytic center. Consequently, the use of an inert, weakly

coordinating IL in these cases can result in a clear enhancement of catalytic activity as

some ILs are known to combine high solvation power of polar catalyst complexes

(polarity) with the weak coordination (nucleophilicity).145 ILs formed by treatment of

a halide salt with a Lewis acid (such as chloroaluminate or chlorostannate melts)

generally act both as solvent and as co-catalyst in transition metal catalysis. Both the

cation and the anion of an IL can act as a ligand or ligand precursor for a transition

metal complex dissolved in the ionic liquid.31,234

1.9 ILs FOR SYNTHESIS AND STABILIZATION OF METAL NANOPARTICLES

Nanoparticles (NPs) can be considered as assemblies of hundreds to thousands of atoms

and a size in the range of 1nm- 50nm. Metal nanoparticles (M-NPs) are of significant

interest for technological applications in several areas of science and industry, especially

in catalysis due to their high surface activity. The controlled and reproducible synthesis of

defined and stable M-NPs with a small size distribution is very important for a range of

applications.235-241 Kinetically stable small (<5nm) M-NPs agglomerate to

thermodynamically favored larger metal particles. Tendency of M-NPs for aggregation

arises due to the high surface energy and the large surface area. To avoid this coagulation,

M-NPs need to be stabilized with strongly coordinating protective ligand layers that can

Chapter 1

34

provide electrostatic and/or steric protection like polymers and surfactants.242-245 ILs can

be an alternative to such ligand layers (Figure 1.11). ILs may be seen to act as a “novel

nanosynthetic template”246 that can help in stabilizing M-NPs on the basis of their ionic

nature,247 high polarity, high dielectric constant and supramolecular network (without the

need of additional protective ligands) (Figure 1.12)7,248-251.

Figure 1.11: Stabilization of metal nanoparticles (M-NP)through protective ligand

stabilizers or using ILs.252

When mixed with other molecules or M-NPs, ILs become nanostructured materials

with polar and non-polar domains.253-255 This kind of nanometer-scale structuring

in RTILs has been observed by molecular simulation for ILs belonging to the

1-alkyl-3-methylimidazolium family with hexafluorophosphate or with

bis(trifluoromethylsulfonyl)amide as the anions. In case of ILs bearing alkyl side

chains longer than or equal to C4, aggregation of the alkyl chains in non-polar

domains has been observed. These domains generate a three-dimensional network

of charged or polar ionic channels (formed by anions and by the imidazolium

cation rings) (Figure 1.12). As the length of the alkyl chain increases, the non-

polar domains become larger and more connected and cause swelling of the ionic

network.256 In other words, ILs are nanostructurally organized with non-polar regions

arising from clustering of the alkyl chains and ionic networks arising from the ordering of

the charged anions and imidazolium rings of the cations.257 The combination of

Chapter 1

35

undirected Coulomb forces and directed hydrogen bonds leads to a high attraction of the

IL building units. This phenomenon also forms the basis for their (high) viscosity,

negligible vapor pressure and three-dimensional constitution. The IL network properties

are well suited for the synthesis of defined nano-scaled metal colloid structures even in

the absence of stabilizing ligands (Figure 1.12).7,248,249

Figure 1.12: The inclusion of M-NPs in the supramolecular IL network with

electrostatic and steric (= electrosteric) stabilization is indicated through

the formation of the suggested primary anion layer forming around the

M-NPs.252

Chapter 1

36

1.9.1 Synthesis of metal nanoparticles (M-NPs) in ILs

M-NPs can be synthesized in ILs258 through chemical reduction,259-265

decomposition221,266-268 or by means of photochemical reduction269,270 or electro-

reduction271 of metal salts, where the metal atom is in a formally positive oxidation

state. They can also be generated by the decomposition of metal carbonyls with zero-

valent metal atoms246,265,272,273 (without the need of extra stabilizing molecules or

organic solvents).242,243,248,249,274,275 A range of M-NPs have been prepared in ILs from

compounds where the metal is in a formally positive oxidation state Mn+. Such M-NPs

then include, for example, the main-group metals and metalloids Al,276,277 Te278,279

and the transition metals Ru,280 Rh,262 Ir,222 Pt,223 Ag259,281 and Au.226

Alternatively, functionalized ILs have also been used where the IL could work as both

a reducing agent as well as stabilizer for the synthesis of M-NPs. Moreover, in

comparison with non-functionalized imidazolium-ILs, functionalized imidazolium-

ILs can stabilize aqueous dispersion of metal NPs much more efficiently because of

the special functional group. Thiol-functionalized,226,282,283 ether-functionalized,284

carboxylic acid– functionalized,285 amino-functionalized,285,286 and hydroxyl-

functionalized227 imidazolium-ILs have been used to synthesize aqueous dispersion of

noble (primarily gold) metal NPs.

Amongst the methods mentioned above, the reduction of metal salts is the most

utilized method for generating M-NPs in solution and also in ILs in general. Many

different types of reducing agents are used, like gases (molecular hydrogen) organic

(citrate, ascorbic acid, imidazolium cation of IL) and inorganic (NaBH4, SnCl2)

materials.252 However, the applicability of any IL in chemical reduction method

depends upon its stability in the reaction mixture. ILs are quite often known to react

with strong bases, acids, some reducing agents (e.g. NaBH4, LiAlH4, R3Al, etc.) or

may decompose at relatively high reaction temperatures. In this context mild reducing

agents (such as alcohols or molecular hydrogen) may be opted for.252

Chapter 1

37

In the direct route of chemical reduction (Figure 1.13), a metal precursor is dissolved

in an ionic liquid and is reduced with a suitable reducing agent (which produces lesser

by-products that can decompose an IL). Heating if required, is carried out at the

temperatures below the decomposition temperature of the ionic liquid. It has been

postulated that if a metal precursor is completely soluble in an ionic liquid, use of an

additional solvent may no longer be required. In such cases, the reaction rate can be

accelerated by stirring, heating, ultrasonic treatment or addition of a few drops of a

suitable solvent.287 Some examples describing the preparation of NPs in ILs via the

chemical route can be found in the literature.222,223,225,229,242,288-290

Figure 1.13: Preparation of NPs in ILs via direct route252

Using the direct method, not all the requirements for the formation of NPs can be met

in an IL. Hence, an indirect method for the synthesis of NPs has been proposed. The

NPs of interest are prepared using a convenient and suitable combination of stabilizer,

metal precursor and reducing agent in an organic solvent and then transferred into the

required IL(Figure 1.14).291

Figure 1.14: Preparation of NPs in ILs via indirect route252

However, in this indirect method, the addition of the stabilizer can be replaced with

the addition of a suitable IL which can prevent the particle agglomeration and provide

extended stability. As an example, carboxylic acid and amino-functionalized ILs

Chapter 1

38

[C1mim]Cl (1-carboxylmethyl-3-methylimidazolium chloride) and [Aemim]Br

(1-aminoethyl-3-methylimidazolium bromide) were used as the stabilizer for the

synthesis of gold and platinum metal nanoparticles in aqueous solution.285 The

mechanism of stabilization has been proposed due to the interactions between

imidazolium ions/functional groups in ILs and the metal atoms.

1.9.2 Stabilization of M-NPs using ILs: DLVO theory and other effects

The basic and most common theory for interaction of two particles in a dispersion is the

DLVO theory (Derjaguin, Landau, Verwey and Overbeek theory) considered as a

combination of repulsive coulombic and the attractive van der Waals forces. The DLVO

theory considers initially charged colloidal particles whereby the electric charges are

uniformly distributed over their surface. The total energy potential VT (or the DLVO

potential) of the interaction between two particles is then described as the sum of

attractive (van der Waals) forces and repulsive forces (due to a double layer of counter

ions). The height of the overall potential barrier VT determines, whether the particles are

stable (the kinetic energy Ek of particle motion is less than VT i.e. Ek>VT ) or not

(Ek>VT).287

Some assumptions and simplifications involved with DLVO theory are often

introduced. It is assumed that the particle surfaces are flat and the charge density is

homogeneous and remains so, even when particles approach each other. Moreover,

there is no change in the concentration of the counter ions which cause the electric

potential. The solvent itself influences only through its dielectric constant.

It is quite clear that the surface of a particle is not flat and the charge density changes

when two particles approach each other. Thus it is evident that the theory is being

limited to certain assumptions and can thus, only approximate the real-life interactions

of two particles.252

Concerning NPs and their interactions, the anion has been considered to interact with

the unsaturated surface of the electrophilic NPs.292 Thus, the NPs with their anion

layer assume a negative charge and turn into a large multi-negative anion. The

repulsion between two such negatively charged NPs is the Coulomb part of the

DLVO theory. The stability of colloids is a balance between Coulomb forces and

van der Waals attraction. A measure of the stability of a colloid is the thickness of the

Chapter 1

39

Debye layer, which is the sum of the layers of counter ions surrounding the particle.

The thicker the Debye layer, the more stable is the particle because the distance to the

next particle is greater and the van der Waals attraction is reduced. Finke et al. studied

the stability of colloids in different solvents and found that higher the dielectric

constant of the medium, the better is the stabilization of the colloid.261

The DLVO theory has certain limitations. It can only be applied to dilute systems

(<5× 10−2mol/l) and not even for higher concentrations. It cannot be applied to ions

with multiple charges and sterically stabilized systems.293 Nowadays, the DLVO

theory has been supplemented with “extra-DLVO” forces which include effects such

as hydrogen bonding, hydrophobicity, steric interactions and viscous forces.252

1.10 CHALLENGES WITH IONIC LIQUIDS

Unique properties of ILs can be exploited for innumerable applications. However

there are few disadvantages that restrict their use for certain specific applications.

1.10.1 Cost/ Economic perspective

Cost is a major challenge to be encountered in synthesizing ILs on an industrial scale. A

kilogram of ionic liquid used to cost about 30,000-fold greater than a common organic

solvent such as acetone. Renner38 reported that this cost could be reduced to

approximately 1000-fold depending on the composition of ionic liquid and the scale of

production. Wagner and Uerdingen294 anticipated that the price of cation systems based

on imidazole will be in the range of € 50 kg−1–100 kg−1, if larger quantities of ILs are

produced. The price can be lowered even below € 25 kg−1 if ILs are prepared with cheaper

cation sources on a ton scale. Further, another estimation was done by Wassersheid and

Haumann.295 They expected that for ‘bulk ILs” choosing proper (relatively cheap) cations

and anions lead to prices approximately € 30 l−1 for production rates of multi-ton.

Moreover, scientists emphasize that although the price of the ILs may look

discouraging but still, the essential factor is the price to performance ratio. If the

performance of an IL is extremely high as compared to that of the material (solvent) it

aims to replace, less amounts of the IL may be needed for a given specific job296,

thereby totally or partially overcoming the price disadvantage.

Chapter 1

40

1.10.1 Green aspects of ILs; Recyclability and Disposal

A problem is faced while manufacturing ILs and that needs to be tackled. This is the

use of VOCs in the manufacture of ILs. Recently, some advancement has been

achieved in the solventless syntheses of ILs. For example, 1-alkyl-3-

methylimidazolium halides have been synthesized in open containers in a microwave

oven without any VOCs by Varma and Namboodiri at the Environmental Protection

Agency of U.S.,2001.38

Recycling of ILs is another important issue that concerns the researchers working with

them. Many processes for cleaning up ILs involve washing with water or VOCs which

creates another waste stream. This problem has been solved by adopting supercritical

extraction technologies to recover the dissolved organic compounds from ILs or using

membrane separation processes. A green solvent, which has been discovered and solves

all the problems and recovers various kinds of solutes from ILs without cross

contamination, are supercritical fluids (SCFs).The advantages of using SCFs as extraction

medium include low cost, nontoxic nature, recoverability and ease of separation from the

products. SCFs have been adapted for product recovery from ILs and supercritical fluid

extraction (SCFE) is shown to be a viable technique with the additional benefits of

environmental sustainability and pure product recovery.297 Among the SCFs, an

inexpensive and readily available one, scCO2 has become a partner of IL and two

environmentally benign solvents have been utilized together in several applications. The

volatile and non-polar scCO2 forms different two-phase systems with non-volatile and

polar ILs. The product recovery process with these systems is based on the principle that

scCO2is soluble in ILs, but ILs are not soluble in scCO2.297 Since most of the organic

compounds are soluble in scCO2, with the high solubility of scCO2 in ILs, these products

are transferred from the ionic liquid to the supercritical phase.

Apart from general green credentials of ILs (low vapor pressure, low flammability

and causing lesser air pollution problems) eco-toxicological risk profiles must also be

addressed. According to Jastorff et al.,298 the toxicity of ILs is roughly driven by the

head group, the side chain, and the anion. Currently, the biological effects of ILs have

resulted in increasing reports, which have dealt mainly with the influence of the alkyl

side chain length of various head groups of ILs. Pernak et al.299-303 pointed out that

their antimicrobial activity increased within increasing alkyl chain length on

Chapter 1

41

pyridinium, imidazolium, and quaternary ammonium salts. Some studies have

reported that varying the anion had minimal effects on the toxicities of several

pyridinium and imidazolium compounds and indicated that the toxicity of ILs was

largely driven by the alkyl chain branching and hydrophobicity of the cation.301,304-306

However, in particular, some ILs with fluorine-containing anions were suggested to

be relatively toxic because the anions were hydrolyzed to fluoride in the aqueous

solution and the fluoride had a toxic effect.307,308

Thus, designing of ILs and their applications in the field of research at every level

should deal with toxicity and biodegradability issues wherever possible.

Chapter 1

42

REFERENCES

1. Welton T. Room-Temperature Ionic Liquids. Solvents for Synthesis and

Catalysis. Chemical Reviews. 1999;99(8):2071-2084.

2. Keskin S, Kayrak-Talay D, Akman U, Hortaçsu Ö. A review of ionic liquids

towards supercritical fluid applications. The Journal of Supercritical Fluids.

2007;43(1):150-180.

3. Sugden S, Wilkins H. CLXVII.-The parachor and chemical constitution. Part

XII. Fused metals and salts. Journal of the Chemical Society (Resumed).

1929:1291-1298.

4. Gorman J. Faster, better, cleaner?: New liquids take aim at old-fashioned

chemistry. Science News. 2001;160(10):156-158.

5. Wilkes JS, Levisky JA, Wilson RA, Hussey CL. Dialkylimidazolium

chloroaluminate melts: a new class of room-temperature ionic liquids for

electrochemistry, spectroscopy and synthesis. Inorganic Chemistry.

1982;21(3):1263-1264.

6. Fannin AA, Floreani DA, King LA, Landers JS, Piersma BJ, Stech DJ,

Vaughn RL, Wilkes JS, Williams John L. Properties of 1,3-

dialkylimidazolium chloride-aluminum chloride ionic liquids. 2. Phase

transitions, densities, electrical conductivities, and viscosities. The Journal of

Physical Chemistry. 1984;88(12):2614-2621.

7. Dupont J. On the solid, liquid and solution structural organization of

imidazolium ionic liquids. Journal of the Brazilian Chemical Society.

2004;15:341-350.

8. Brennecke JF, Maginn EJ. Ionic liquids: Innovative fluids for chemical

processing. AIChE Journal. 2001;47(11):2384-2389.

9. Plechkova NV, Seddon KR. Applications of ionic liquids in the chemical

industry. Chemical Society Reviews. 2008;37(1):123-150.

10. Weingärtner H. Understanding ionic liquids at the molecular level: facts,

problems, and controversies. Angewandte Chemie International Edition.

2007;47(4):654-670.

Chapter 1

43

11. Wasserscheid P, Welton T. Ionic Liquids in Synthesis: John Wiley & Sons;

2008.

12. Davis J, J. H. Task-specific ionic liquids. Chemistry Letters. 2004;33(9):1072-

1077.

13. MacFarlane DR, Pringle JM, Johansson KM, Forsyth M. Lewis base ionic

liquids. Chemical Communications. 2006(18):1905-1917.

14. Duan Z, Gu Y, Deng Y. Green and moisture-stable Lewis acidic ionic liquids

(choline chloride·xZnCl2) catalyzed protection of carbonyls at room

temperature under solvent-free conditions. Catalysis Communications.

2006;7(9):651-656.

15. Hajipour A, Rafiee F. Basic ionic liquids. A short review. Journal of the

Iranian Chemical Society. 2009;6(4):647-678.

16. Bonhôte P, Dias A-P, Papageorgiou N, Kalyanasundaram K, Grätzel M.

Hydrophobic, Highly Conductive Ambient-Temperature Molten Salts.

Inorganic Chemistry. 1996;35(5):1168-1178.

17. MacFarlane DR, Meakin P, Sun J, Amini N, Forsyth M. Pyrrolidinium

Imides:  A New Family of Molten Salts and Conductive Plastic Crystal Phases.

The Journal of Physical Chemistry B. 1999;103(20):4164-4170.

18. Golding J, Forsyth S, MacFarlane DR, Forsyth M, Deacon GB.

Methanesulfonate and p-toluenesulfonate salts of the N-methyl-N-

alkylpyrrolidinium and quaternary ammonium cations: novel low cost ionic

liquids. Green Chemistry. 2002;4(3):223-229.

19. Yoshida Y, Muroi K, Otsuka A, Saito G, Takahashi M, Yoko T. 1-Ethyl-3-

methylimidazolium Based Ionic Liquids Containing Cyano Groups: 

Synthesis, Characterization, and Crystal Structure. Inorganic Chemistry.

2004;43(4):1458-1462.

20. Martins MAP, Frizzo CP, Moreira DN, Zanatta N, Bonacorso HG. Ionic

Liquids in Heterocyclic Synthesis. Chemical Reviews. 2008;108(6):2015-

2050.

Chapter 1

44

21. Cheng G, Duan X, Qi X, Lu C. Nitration of aromatic compounds with NO2/air

catalyzed by sulfonic acid-functionalized ionic liquids. Catalysis

Communications. 2008;10(2):201-204.

22. Fei Z, Zhao D, Geldbach TJ, Scopelliti R, Dyson PJ. Brønsted Acidic Ionic

Liquids and Their Zwitterions: Synthesis, Characterization and pKa

Determination. Chemistry – A European Journal. 2004;10(19):4886-4893.

23. Wang C, Guo L, Li H, Wang Y, Weng J, Wu L. Preparation of simple

ammonium ionic liquids and their application in the cracking of

dialkoxypropanes. Green Chemistry. 2006;8(7):603-607.

24. Hajipour AR, Mostafavi M, Ruoho AE. Iodination of Alcohols using

Triphenylphosphine/Iodine in Ionic Liquid under Solvent-Free Conditions.

Organic Preparations and Procedures International. 2009;41(1):87-91.

25. Bicak N. A new ionic liquid: 2-hydroxy ethylammonium formate. Journal of

Molecular Liquids. 2005;116(1):15-18.

26. Zhang R, Meng X, Liu Z, Meng J, Xu C. Isomerization of n-Pentane

Catalyzed by Acidic Chloroaluminate Ionic Liquids. Industrial & Engineering

Chemistry Research. 2008;47(21):8205-8210.

27. Chiappe C, Leandri E, Tebano M. [Hmim][NO3]-an efficient solvent and

promoter in the oxidative aromatic chlorination. Green Chemistry.

2006;8(8):742-745.

28. Elango K, Srirambalaji R, Anantharaman G. Synthesis of N-alkylimidazolium

salts and their utility as solvents in the Beckmann rearrangement. Tetrahedron

Letters. 2007;48(51):9059-9062.

29. Wu Q, Chen H, Han M, Wang D, Wang J. Transesterification of Cottonseed

Oil Catalyzed by Brønsted Acidic Ionic Liquids. Industrial & Engineering

Chemistry Research. 2007;46(24):7955-7960.

30. Bao-You L, Dan-Qian X, Zhen-Yuan X. Electrochemical Synthesis of

Dendritic Polyaniline in Brønsted Acid Ionic Liquids. Chinese Journal of

Chemistry. 2005;23(7):803-805.

Chapter 1

45

31. Wasserscheid P, Keim W. Ionic Liquids—New “Solutions” for Transition

Metal Catalysis. Angewandte Chemie. 2000;39(21):3772-3789.

32. Seddon KR. Ionic Liquids for Clean Technology. Journal of Chemical

Technology & Biotechnology. 1997;68(4):351-356.

33. Ngo HL, LeCompte K, Hargens L, McEwen AB. Thermal properties of

imidazolium ionic liquids. Thermochimica Acta. 2000;357–358(0):97-102.

34. Elaiwi A, Hitchcock PB, Seddon KR, Srinivasan N, Tan Y-M, Welton T, Zora

JA. Hydrogen bonding in imidazolium salts and its implications for ambient-

temperature halogenoaluminate(III) ionic liquids. Journal of the Chemical

Society, Dalton Transactions. 1995(21):3467-3472.

35. Saha S, Hayashi S, Kobayashi A, Hamaguchi H. Crystal structure of 1-butyl-

3-methylimidazolium chloride. A clue to the elucidation of the ionic liquid

structure. Chemistry Letters. 2003(8):740-741.

36. Holbrey JD, Reichert WM, Nieuwenhuyzen M, Johnson S, Seddon KR,

Rogers RD. Crystal polymorphism in 1-butyl-3-methylimidazolium halides:

supporting ionic liquid formation by inhibition of crystallization. Chemical

Communications. 2003(14):1636-1637.

37. Chiappe C, Pieraccini D. Ionic liquids: solvent properties and organic

reactivity. Journal of physical organic chemistry. 2004;18(4):275-297.

38. Renner R. Ionic liquids: an industrial cleanup solution. Environmental Science

& Technology. 2001;35(19):410A-413A.

39. Yang Q, Dionysiou DD. Photolytic degradation of chlorinated phenols in

room temperature ionic liquids. Journal of Photochemistry and Photobiology

A: Chemistry. 2004;165(1):229-240.

40. Holbrey JD, Seddon KR. The phase behaviour of 1-alkyl-3-

methylimidazolium tetrafluoroborates; ionic liquids and ionic liquid crystals.

Journal of the Chemical Society, Dalton Transactions. 1999(13):2133-2140.

41. Wilkes JS, Zaworotko MJ. Air and water stable 1-ethyl-3-methylimidazolium

based ionic liquids. Journal of the Chemical Society, Chemical

Communications. 1992(13):965-967.

Chapter 1

46

42. Zhang S, Sun N, He X, Lu X, Zhang X. Physical properties of ionic liquids:

database and evaluation. Journal of physical and chemical reference data.

2006;35:1475-1517.

43. Gonsior DCN. Ionic Liquids. Modern Methods of Synthesis, Polymerization,

Characterization, and Application. Düsseldorf: Institute of Organic Chemistry

and Macromolecular Chemistry, Heinrich-Heine-University Dusseldorf; 2010.

44. Appleby D, Hussey CL, Seddon KR, Turp JE. Room-temperature ionic liquids

as solvents for electronic absorption spectroscopy of halide complexes.

Nature. 1986;323(16):614-616.

45. Ohno H, Yoshizawa M. Ion conductive characteristics of ionic liquids

prepared by neutralization of alkylimidazoles. Solid State Ionics. 2002;154–

155:303-309.

46. Matsumoto H, Matsuda T, Miyazaki Y. Room temperature molten salts based

on trialkylsulfonium cations and bis (trifluoromethylsulfonyl) imide.

Chemistry Letters. 2000;29(12):1430-1431.

47. Earle MJ, Esperança JMSS, Gilea MA, Canongia Lopes JN, Rebelo LPN,

Magee JW, Seddon KR, Widegren JA. The distillation and volatility of ionic

liquids. Nature. 2006;439(7078):831-834.

48. Wasserscheid P. Chemistry: Volatile times for ionic liquids. Nature.

2006;439(7078):797-797.

49. Bockris JOM, Reddy AKN. Modern electrochemistry. Vol 2: Springer; 2000.

50. Schröder U, Wadhawan JD, Compton RG, Marken F, Suarez PAZ, Consorti

CS, de Souza RF, Dupont J. Water-induced accelerated ion diffusion:

voltammetric studies in 1-methyl-3-[2,6-(S)-dimethylocten-2-yl]imidazolium

tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate and

hexafluorophosphate ionic liquids. New Journal of Chemistry.

2000;24(12):1009-1015.

51. Huddleston JG, Visser AE, Reichert WM, Willauer HD, Broker GA, Rogers

RD. Characterization and comparison of hydrophilic and hydrophobic room

temperature ionic liquids incorporating the imidazolium cation. Green

Chemistry. 2001;3(4):156-164.

Chapter 1

47

52. Takahashi S, Koura N, Kohara S, Saboungi ML, Curtiss LA. Technological

and scientific issues of room-temperature molten salts. Plasmas &amp; Ions.

1999;2(3–4):91-105.

53. Seddon KR, Stark A, Torres MJ. Influence of chloride, water, and organic

solvents on the physical properties of ionic liquids. Pure Appl. Chem.

2000;72(12):2275-2287.

54. Jacquemin J, Husson P, Padua AAH, Majer V. Density and viscosity of

several pure and water-saturated ionic liquids. Green Chemistry.

2006;8(2):172-180.

55. Perry RL, Jones KM, Scott WD, Liao Q, Hussey CL. Densities, Viscosities,

and Conductivities of Mixtures of Selected Organic Cosolvents with the Lewis

Basic Aluminum Chloride + 1-Methyl-3-ethylimidazolium Chloride Molten

Salt. Journal of Chemical & Engineering Data. 1995;40(3):615-619.

56. Liao Q, Hussey CL. Densities, Viscosities, and Conductivities of Mixtures of

Benzene with the Lewis Acidic Aluminum Chloride + 1-Methyl-3-

ethylimidazolium Chloride Molten Salt. Journal of Chemical & Engineering

Data. 1996;41(5):1126-1130.

57. Dzyuba SV, Bartsch RA. Influence of Structural Variations in 1-

Alkyl(aralkyl)-3-Methylimidazolium Hexafluorophosphates and

Bis(trifluoromethylsulfonyl)imides on Physical Properties of the Ionic

Liquids. ChemPhysChem. 2002;3(2):161-166.

58. Scammells PJ, Scott JL, Singer RD. Ionic Liquids: The Neglected Issues.

Australian Journal of Chemistry. 2005;58(3):155-169.

59. Deetlefs M, Seddon KR. Ionic liquids: fact and fiction. Chimica oggi.

2006;24(2):16-23.

60. van Rantwijk F, Sheldon RA. Biocatalysis in Ionic Liquids. Chemical

Reviews. 2007;107(6):2757-2785.

61. Taft R, Abboud J-L, Kamlet M, Abraham M. Linear solvation energy

relations. J Solution Chem. 1985;14(3):153-186.

Chapter 1

48

62. Muldoon MJ, Gordon CM, Dunkin IR. Investigations of solvent-solute

interactions in room temperature ionic liquids using solvatochromic dyes.

Journal of the Chemical Society, Perkin Transactions 2. 2001(4):433-435.

63. Yuan H, Souvignet I, Olesik SV. High-performance size exclusion

chromatography using enhanced-fluidity liquid mobile phases. Journal of

chromatographic science. 1997;35(9):409-416.

64. Aki SNVK, Brennecke JF, Samanta A. How polar are room-temperature ionic

liquids? Chemical Communications. 2001(5):413-414.

65. Crowhurst L, Mawdsley PR, Perez-Arlandis JM, Salter PA, Welton T.

Solvent-solute interactions in ionic liquids. Physical Chemistry Chemical

Physics. 2003;5(13):2790-2794.

66. Reichardt C. Solvatochromism, thermochromism, piezochromism,

halochromism, and chiro-solvatochromism of pyridinium N-phenoxide betaine

dyes. Chemical Society Reviews. 1992;21(3):147-153.

67. Poole SK, Shetty PH, Poole CF. Chromatographic and spectroscopic studies

of the solvent properties of a new series of room-temperature liquid

tetraalkylammonium sulfonates. Analytica Chimica Acta. 1989;218:241-264.

68. Shetty PH, Youngberg PJ, Kersten BR, Poole CF. Solvent properties of liquid

organic salts used as mobile phases in microcolumn reversed-phase liquid

chromatography. Journal of Chromatography A. 1987;411:61-79.

69. Coddens ME, Furton KG, Poole CF. Synthesis and gas chromatographic

stationary phase properties of alkylammonium thiocyanates. Journal of

Chromatography A. 1986;356:59-77.

70. Furton KG, Poole SK, Poole CF. Gas chromatographic stationary phase

properties of two room-temperature liquid organi salts. Analytica Chimica

Acta. 1987;192:49-61.

71. Furton KG, Poole CF. Thermodynamic characteristics of solute—solvent

interactions in liquid organic salt solvents, studied by gas chromatography.

Journal of Chromatography A. 1987;399:47-67.

Chapter 1

49

72. Pomaville RM, Poole SK, Davis LJ, Poole CF. Solute—solvent interactions in

tetra-n-butylphosphonium salts studied by gas chromatography. Journal of

Chromatography A. 1988;438:1-14.

73. Anderson JL, Ding J, Welton T, Armstrong DW. Characterizing Ionic Liquids

On the Basis of Multiple Solvation Interactions. Journal of the American

Chemical Society. 2002;124(47):14247-14254.

74. Earle MJ, Engel BS, Seddon KR. Keto-Enol Tautomerism as a Polarity

Indicator in Ionic Liquids. Australian Journal of Chemistry.

2004;57(2):149-150.

75. Reichardt C. Polarity of ionic liquids determined empirically by means of

solvatochromic pyridinium N-phenolate betaine dyes. Green Chemistry.

2005;7(5):339-351.

76. Carmichael AJ, Seddon KR. Polarity study of some 1-alkyl-3-

methylimidazolium ambient-temperature ionic liquids with the solvatochromic

dye, Nile Red. Journal of physical organic chemistry. 2000;13(10):591-595.

77. Abraham MH, Acree Jr WE. Comparative analysis of solvation and selectivity

in room temperature ionic liquids using the Abraham linear free energy

relationship. Green Chem. 2006;8(10):906-915.

78. Swatloski RP, Spear SK, Holbrey JD, Rogers RD. Dissolution of Cellose with

Ionic Liquids. Journal of the American Chemical Society. 2002;124(18):4974-

4975.

79. Dupont J, Consorti CS, Spencer J. Room temperature molten salts: neoteric"

green" solvents for chemical reactions and processes. Journal of the Brazilian

Chemical Society. 2000;11(4):337-344.

80. Mutelet F, Butet V, Jaubert JN. Application of inverse gas chromatography

and regular solution theory for characterization of ionic liquids. Industrial &

Engineering Chemistry Research. 2005;44(11):4120-4127.

81. Reichardt C. Solvatochromic Dyes as Solvent Polarity Indicators. Chemical

Reviews. 1994;94(8):2319-2358.

Chapter 1

50

82. Dixit S, Crain J, Poon WCK, Finney JL, Soper AK. Molecular segregation

observed in a concentrated alcohol-water solution. Nature.

2002;416(6883):829-832.

83. Cammarata L, Kazarian SG, Salter PA, Welton T. Molecular states of water in

room temperature ionic liquids. Physical Chemistry Chemical Physics.

2001;3(23):5192-5200.

84. Köddermann T, Wertz C, Heintz A, Ludwig R. The Association of Water in

Ionic Liquids: A Reliable Measure of Polarity. Angewandte Chemie

International Edition. 2006;45(22):3697-3702.

85. Poole CF, Poole SK. Extraction of organic compounds with room temperature

ionic liquids. Journal of chromatography. 2010;1217(16):2268-2286.

86. Kabo GJ, Blokhin AV, Paulechka YU, Kabo AG, Shymanovich MP, Magee

JW. Thermodynamic Properties of 1-Butyl-3-methylimidazolium

Hexafluorophosphate in the Condensed State. Journal of Chemical &

Engineering Data. 2004;49(3):453-461.

87. Zhao H, Xia S, Ma P. Use of ionic liquids as ‘green’solvents for extractions.

Journal of chemical technology and biotechnology. 2005;80(10):1089-1096.

88. Huddleston JG, Rogers RD. Room temperature ionic liquids as novel media

for ‘clean’liquid–liquid extraction. Chem. Commun. 1998(16):1765-1766.

89. Carter EB, Culver SL, Fox PA, Goode RD, Ntai I, Tickell MD, Traylor RK,

Hoffman NW, Davis Jr JH. Sweet success: ionic liquids derived from non-

nutritive sweeteners. Chemical Communications. 2004(6):630-631.

90. Shariati A, Peters CJ. High-pressure phase equilibria of systems with ionic

liquids. The Journal of Supercritical Fluids. 2005;34(2):171-176.

91. Davis Jr JH, Fox PA. From curiosities to commodities: ionic liquids begin the

transition. Chemical Communications. 2003(11):1209-1212.

92. Kumar V, Olsen CE, Schäffer SJC, Parmar VS, Malhotra SV. Synthesis and

applications of novel bis (ammonium) chiral ionic liquids derived from

isomannide. Organic Letters. 2007;9(20):3905-3908.

Chapter 1

51

93. McCamley K, Warner NA, Lamoureux MM, Scammells PJ, Singer RD.

Quantification of chloride ion impurities in ionic liquids using ICP-MS

analysis. Green Chemistry. 2004;6(7):341-344.

94. Holbrey JD, Reichert WM, Swatloski RP, Broker GA, Pitner WR, Seddon

KR, Rogers RD. Efficient, halide free synthesis of new, low cost ionic liquids:

1, 3-dialkylimidazolium salts containing methyl-and ethyl-sulfate anions.

Green Chem. 2002;4(5):407-413.

95. Karodia N, Guise S, Newlands C, Andersen JA. Clean catalysis with ionic

solvents—phosphonium tosylates for hydroformylation. Chemical

Communications. 1998(21):2341-2342.

96. Matsumoto H, Kageyama H, Miyazaki Y. Room temperature ionic liquids

based on small aliphatic ammonium cations and asymmetric amide anions.

Chemical Communications. 2002(16):1726-1727.

97. Jain N, Kumar A, Chauhan S, Chauhan SMS. Chemical and biochemical

transformations in ionic liquids. Tetrahedron. 2005;61(5):1015-1060.

98. J. Dyson P, C. Grossel M, Srinivasan N, Vine T, Welton T, J. Williams D, J.

P. White A, Zigras T. Organometallic synthesis in ambient temperature

chloroaluminate(III) ionic liquids. Ligand exchange reactions of ferrocene.

Journal of the Chemical Society, Dalton Transactions. 1997(19):3465-3469.

99. Varma RS, Namboodiri VV. An expeditious solvent-free route to ionic liquids

using microwaves. Chemical Communications. 2001(7):643-644.

100. Dzyuba SV, Bartsch RA. Efficient synthesis of 1-alkyl(aralkyl)-3-

methyl(ethyl)imidazolium halides: Precursors for room-temperature ionic

liquids. Journal of Heterocyclic Chemistry. 2001;38(1):265-268.

101. MacFarlane DR, Golding J, Forsyth S, Forsyth M, Deacon GB. Low viscosity

ionic liquids based on organic salts of the dicyanamide anion. Chemical

Communications. 2001(16):1430-1431.

102. Dzyuba SV, Bartsch RA. Expanding the polarity range of ionic liquids.

Tetrahedron Letters. 2002;43(26):4657-4659.

Chapter 1

52

103. Reichardt C. Solvents and Solvent Effects in Organic Chemistry: John Wiley

& Sons; 2006.

104. Gathergood N, Garcia MT, Scammells PJ. Biodegradable ionic liquids: Part I.

Concept, preliminary targets and evaluation. Green Chemistry. 2004;6(3):166-

175.

105. Gathergood N, Scammells PJ. Design and preparation of room-temperature

ionic liquids containing biodegradable side chains. Australian Journal of

Chemistry. 2002;55(9):557-560.

106. Wasserscheid P, Drie, van Hal R, Steffens HC, Zimmermann J. New,

functionalised ionic liquids from Michael-type reactions-a chance for

combinatorial ionic liquid development. Chemical Communications.

2003(16):2038-2039.

107. Wasserscheid P, Bosmann A, Bolm C. Synthesis and properties of ionic

liquids derived from the 'chiral pool'. Chemical Communications.

2002(3):200-201.

108. Pégot B, Vo-Thanh G, Gori D, Loupy A. First application of chiral ionic

liquids in asymmetric Baylis–Hillman reaction. Tetrahedron Letters.

2004;45(34):6425-6428.

109. Ding J, Desikan V, Han X, Xiao TL, Ding R, Jenks WS, Armstrong DW. Use

of Chiral Ionic Liquids as Solvents for the Enantioselective

Photoisomerization of Dibenzobicyclo[2.2.2]octatrienes. Organic Letters.

2004;7(2):335-337.

110. Howarth J, Hanlon K, Fayne D, McCormac P. Moisture Stable

Dialkylimidazolium Salts as Heterogeneous and Homogeneous Lewis Acids in

the Diels-Alder Reaction. Tetrahedron Letters. 1997;38(17):3097-3100.

111. Luo S, Mi X, Zhang L, Liu S, Xu H, Cheng J-P. Functionalized Chiral Ionic

Liquids as Highly Efficient Asymmetric Organocatalysts for Michael Addition to

Nitroolefins. Angewandte Chemie International Edition. 2006;45(19):3093-3097.

112. Malhotra SV, Wang Y. Application of chiral ionic liquids in the copper

catalyzed enantioselective 1,4-addition of diethylzinc to enones. Tetrahedron:

Asymmetry. 2006;17(7):1032-1035.

Chapter 1

53

113. Biedroń T, Kubisa P. Ionic liquids as reaction media for polymerization

processes: atom transfer radical polymerization (ATRP) of acrylates in ionic

liquids. Polymer International. 2003;52(10):1584-1588.

114. Biedroń T, Kubisa P. Radical polymerization in a chiral ionic liquid: Atom

transfer radical polymerization of acrylates. Journal of Polymer Science Part

A: Polymer Chemistry. 2005;43(15):3454-3459.

115. Ma H, Wan X, Chen X, Zhou Q. Design and synthesis of novel chiral ionic

liquids and their application in free radical polymerization of methyl

methacrylate. Chinese journal of polymer science. 2003;21(3):265-270.

116. Ding J, Welton T, Armstrong DW. Chiral Ionic Liquids as Stationary Phases

in Gas Chromatography. Analytical Chemistry. 2004;76(22):6819-6822.

117. Rizvi SAA, Shamsi SA. Synthesis, Characterization, and Application of Chiral

Ionic Liquids and Their Polymers in Micellar Electrokinetic Chromatography.

Analytical Chemistry. 2006;78(19):7061-7069.

118. Baudoux J, Judeinstein P, Cahard D, Plaquevent J-C. Design and synthesis of

novel ionic liquid/liquid crystals (IL2Cs) with axial chirality. Tetrahedron

Letters. 2005;46(7):1137-1140.

119. Tosoni M, Laschat S, Baro A. Synthesis of Novel Chiral Ionic Liquids and

Their Phase Behavior in Mixtures with Smectic and Nematic Liquid Crystals.

Helvetica Chimica Acta. 2004;87(11):2742-2749.

120. Clavier H, Boulanger L, Audic N, Toupet L, Mauduit M, Guillemin J-C.

Design and synthesis of imidazolinium salts derived from (l)-valine.

Investigation of their potential in chiral molecular recognition. Chemical

Communications. 2004(10):1224-1225.

121. Levillain J, Dubant G, Abrunhosa I, Gulea M, Gaumont A-C. Synthesis and

properties of thiazoline based ionic liquids derived from the chiral pool.

Chemical Communications. 2003(23):2914-2915.

122. Ishida Y, Miyauchi H, Saigo K. Design and synthesis of a novel imidazolium-

based ionic liquid with planar chirality. Chemical Communications.

2002(19):2240-2241.

Chapter 1

54

123. Ishida Y, Sasaki D, Miyauchi H, Saigo K. Design and synthesis of novel

imidazolium-based ionic liquids with a pseudo crown-ether moiety:

diastereomeric interaction of a racemic ionic liquid with enantiopure europium

complexes. Tetrahedron Letters. 2004;45(51):9455-9459.

124. Harris KR, Kanakubo M, Woolf LA. Temperature and Pressure Dependence

of the Viscosity of the Ionic Liquids 1-Methyl-3-octylimidazolium

Hexafluorophosphate and 1-Methyl-3-octylimidazolium Tetrafluoroborate.

Journal of Chemical & Engineering Data. 2006;51(3):1161-1167.

125. Okoturo OO, VanderNoot TJ. Temperature dependence of viscosity for room

temperature ionic liquids. Journal of Electroanalytical Chemistry.

2004;568:167-181.

126. Fortunato R, Branco LC, Afonso CAM, Benavente J, Crespo JG. Electrical

impedance spectroscopy characterisation of supported ionic liquid membranes.

Journal of Membrane Science. 2006;270(1–2):42-49.

127. Domańska U, Marciniak A. Phase behaviour of 1-hexyloxymethyl-3-methyl-

imidazolium and 1,3-dihexyloxymethyl-imidazolium based ionic liquids with

alcohols, water, ketones and hydrocarbons: The effect of cation and anion on

solubility. Fluid Phase Equilibria. 2007;260(1):9-18.

128. Fernández A, Torrecilla JS, García J, Rodríguez F. Thermophysical Properties

of 1-Ethyl-3-methylimidazolium Ethylsulfate and 1-Butyl-3-

methylimidazolium Methylsulfate Ionic Liquids. Journal of Chemical &

Engineering Data. 2007;52(5):1979-1983.

129. Malatesta V, Neri C, Wis ML, Montanari L, Millini R. Thermal and

Photodegradation of Photochromic Spiroindolinenaphthooxazines and -

pyrans:  Reaction with Nucleophiles. Trapping of the Merocyanine

Zwitterionic Form. Journal of the American Chemical Society.

1997;119(15):3451-3455.

130. Hori M, Aoki Y, Maeda S, Tatsumi R, Hayakawa S. Thermal Stability of Ionic

Liquids as an Electrolyte for Lithium-Ion Batteries. ECS Transactions.

2010;25(36):147-153.

Chapter 1

55

131. Umecky T, Kanakubo M, Ikushima Y. Self-diffusion coefficients of 1-butyl-3-

methylimidazolium hexafluorophosphate with pulsed-field gradient spin-echo

NMR technique. Fluid Phase Equilibria. 2005;228–229:329-333.

132. Lyčka A, Doleček R, Šimûnek P, Macháček V. 15N NMR spectra of some

ionic liquids based on 1,3-disubstituted imidazolium cations. Magnetic

Resonance in Chemistry. 2006;44(5):521-523.

133. Armstrong JP, Hurst C, Jones RG, Licence P, Lovelock KRJ, Satterley CJ,

Villar-Garcia IJ. Vapourisation of ionic liquids. Physical Chemistry Chemical

Physics. 2007;9(8):982-990.

134. Wang Q, Baker GA, Baker SN, Colón LA. Surface confined ionic liquid as a

stationary phase for HPLC. Analyst. 2006;131(9):1000-1005.

135. Zhao D, Liao Y, Zhang Z. Toxicity of Ionic Liquids. CLEAN – Soil, Air,

Water. 2007;35(1):42-48.

136. Matsumoto M, Mochiduki K, Kondo K. Toxicity of ionic liquids and organic

solvents to lactic acid-producing bacteria. Journal of Bioscience and

Bioengineering. 2004;98(5):344-347.

137. Stolte S, Matzke M, Arning J, Boschen A, Pitner W-R, Welz-Biermann U,

Jastorff B, Ranke J. Effects of different head groups and functionalised side

chains on the aquatic toxicity of ionic liquids. Green Chemistry.

2007;9(11):1170-1179.

138. Docherty KM, Kulpa JCF. Toxicity and antimicrobial activity of imidazolium

and pyridinium ionic liquids. Green Chemistry. 2005;7(4):185-189.

139. Tao G-h, He L, Sun N, Kou Y. New generation ionic liquids: cations derived

from amino acids. Chemical Communications. 2005(28):3562-3564.

140. Vrikkis RM, Fraser KJ, Fujita K, Macfarlane DR, Elliott GD. Biocompatible

Ionic Liquids: A New Approach for Stabilizing Proteins in Liquid

Formulation. Journal of biomechanical engineering. 2009;131(7):074154.

141. Rogers R, Seddon KR. Ionic liquids: industrial applications for green

chemistry, ACS Symposium Series 818: American Chemical Society,

Washington, DC; 2002.

Chapter 1

56

142. Earle MJ, Seddon KR. Ionic liquids. Green solvents for the future. Pure and

Applied Chemistry. 2000;72(7):1391-1398.

143. Greaves TL, Drummond CJ. Protic Ionic Liquids: Properties and Applications.

Chemical Reviews. 2007;108(1):206-237.

144. Anderson JL, Armstrong DW, Wei G-T. Ionic Liquids in Analytical

Chemistry. Analytical Chemistry. 2006;78(9):2892-2902.

145. Pârvulescu VI, Hardacre C. Catalysis in Ionic Liquids. Chemical Reviews.

2007;107(6):2615-2665.

146. Stark A, L. MacLean B, D. Singer R. 1-Ethyl-3-methylimidazolium

halogenoaluminate ionic liquids as solvents for Friedel-Crafts acylation

reactions of ferrocene. Journal of the Chemical Society, Dalton Transactions.

1999(1):63-66.

147. Ranu BC, Banerjee S, Jana R. Ionic liquid as catalyst and solvent: the

remarkable effect of a basic ionic liquid, [bmIm]OH on Michael addition and

alkylation of active methylene compounds. Tetrahedron. 2007;63(3):776-782.

148. Iranpoor N, Firouzabadi H, Azadi R. A new diphenylphosphinite ionic liquid

(IL-OPPh2) as reagent and solvent for highly selective bromination,

thiocyanation or isothiocyanation of alcohols and trimethylsilyl and

tetrahydropyranyl ethers. Tetrahedron Letters. 2006;47(31):5531-5534.

149. Khadilkar BM, Rebeiro GL. Microwave-Assisted Synthesis of Room-

Temperature Ionic Liquid Precursor in Closed Vessel. Organic Process

Research & Development. 2002;6(6):826-828.

150. Fukumoto K, Ohno H. LCST-Type Phase Changes of a Mixture of Water and

Ionic Liquids Derived from Amino Acids. Angewandte Chemie International

Edition. 2007;46(11):1852-1855.

151. Krossing I, Slattery JM, Daguenet C, Dyson PJ, Oleinikova A, Weingärtner H.

Why Are Ionic Liquids Liquid? A Simple Explanation Based on Lattice and

Solvation Energies. Journal of the American Chemical Society.

2006;128(41):13427-13434.

Chapter 1

57

152. Blanchard LA, Hancu D, Beckman EJ, Brennecke JF. Green processing using

ionic liquids and CO2. Nature. 1999;399(6731):28-29.

153. Wakai C, Oleinikova A, Ott M, Weingärtner H. How Polar Are Ionic Liquids?

Determination of the Static Dielectric Constant of an Imidazolium-based Ionic

Liquid by Microwave Dielectric Spectroscopy. The Journal of Physical

Chemistry B. 2005;109(36):17028-17030.

154. Beyaz A, Oh WS, Reddy VP. Ionic liquids as modulators of the critical

micelle concentration of sodium dodecyl sulfate. Colloids and Surfaces B:

Biointerfaces. 2004;35(2):119-124.

155. El Seoud OA, Koschella A, Fidale LC, Dorn S, Heinze T. Applications of

Ionic Liquids in Carbohydrate Chemistry:  A Window of Opportunities.

Biomacromolecules. 2007;8(9):2629-2647.

156. Gericke M, Schlufter K, Liebert T, Heinze T, Budtova T. Rheological

Properties of Cellulose/Ionic Liquid Solutions: From Dilute to Concentrated

States. Biomacromolecules. 2009;10(5):1188-1194.

157. Byrne N, Howlett PC, MacFarlane DR, Forsyth M. The Zwitterion Effect in

Ionic Liquids: Towards Practical Rechargeable Lithium-Metal Batteries.

Advanced Materials. 2005;17(20):2497-2501.

158. Seki S, Kobayashi Y, Miyashiro H, Ohno Y, Usami A, Mita Y, Watanabe M,

Terada N. Highly reversible lithium metal secondary battery using a room

temperature ionic liquid/lithium salt mixture and a surface-coated cathode

active material. Chemical Communications. 2006(5):544-545.

159. Yang W, Cang H, Tang Y, Wang J, Shi Y. Electrodeposition of tin and

antimony in 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid.

Journal of Applied Electrochemistry. 2008;38(4):537-542.

160. Cao Y, Zhang J, Bai Y, Li R, Zakeeruddin SM, Gra ̈tzel M, Wang P. Dye-

Sensitized Solar Cells with Solvent-Free Ionic Liquid Electrolytes. The

Journal of Physical Chemistry C. 2008;112(35):13775-13781.

Chapter 1

58

161. Kuang D, Uchida S, Humphry-Baker R, Zakeeruddin SM, Grätzel M. Organic

Dye-Sensitized Ionic Liquid Based Solar Cells: Remarkable Enhancement in

Performance through Molecular Design of Indoline Sensitizers. Angewandte

Chemie International Edition. 2008;47(10):1923-1927.

162. Wang P, Zakeeruddin SM, Moser J-E, Grätzel M. A New Ionic Liquid

Electrolyte Enhances the Conversion Efficiency of Dye-Sensitized Solar Cells.

The Journal of Physical Chemistry B. 2003;107(48):13280-13285.

163. Yamanaka N, Kawano R, Kubo W, Kitamura T, Wada Y, Watanabe M,

Yanagida S. Ionic liquid crystal as a hole transport layer of dye-sensitized

solar cells. Chemical Communications. 2005(6):740-742.

164. Weyershausen B, Hell K, Hesse U. Industrial application of ionic liquids as

process aid. Green Chemistry. 2005;7(5):283-287.

165. Bühler G, Feldmann C. Microwave-Assisted Synthesis of Luminescent

LaPO4:Ce,Tb Nanocrystals in Ionic Liquids. Angewandte Chemie

International Edition. 2006;45(29):4864-4867.

166. Adams C, Bradley A, Seddon K. Rapid Communication: The Synthesis of

Mesoporous Materials Using Novel Ionic Liquid Templates in Water.

Australian Journal of Chemistry. 2002;54(11):679-681.

167. Zhou Y, Antonietti M. Preparation of Highly Ordered Monolithic Super-

Microporous Lamellar Silica with a Room-Temperature Ionic Liquid as

Template via the Nanocasting Technique. Advanced Materials.

2003;15(17):1452-1455.

168. Liu Y, Wang M, Li Z, Liu H, He P, Li J. Preparation of Porous

Aminopropylsilsesquioxane by a Nonhydrolytic Sol−Gel Method in Ionic

Liquid Solvent. Langmuir. 2005;21(4):1618-1622.

169. Li Z, Liu Z, Zhang J, Han B, Du J, Gao Y, Jiang T. Synthesis of Single-

Crystal Gold Nanosheets of Large Size in Ionic Liquids. The Journal of

Physical Chemistry B. 2005;109(30):14445-14448.

170. Kaper H, Endres F, Djerdj I, Antonietti M, Smarsly BM, Maier J, Hu Y-S.

Direct Low-Temperature Synthesis of Rutile Nanostructures in Ionic Liquids.

Small. 2007;3(10):1753-1763.

Chapter 1

59

171. Wang T, Kaper H, Antonietti M, Smarsly B. Templating Behavior of a Long-

Chain Ionic Liquid in the Hydrothermal Synthesis of Mesoporous Silica.

Langmuir. 2006;23(3):1489-1495.

172. Cooper ER, Andrews CD, Wheatley PS, Webb PB, Wormald P, Morris RE.

Ionic liquids and eutectic mixtures as solvent and template in synthesis of

zeolite analogues. Nature. 2004;430(7003):1012-1016.

173. Doerr N, Kenesey E, Oetsch C, Ecker A, Pauschitz A, Franek F. Evaluation of

ionic liquids for the application as lubricants. In: D. Dowson MPGD, Lubrecht

AA, eds. Tribology and Interface Engineering Series. Vol Volume 48:

Elsevier; 2005:123-129.

174. Rogers RD, Seddon KR, Volkov S. Green Industrial Applications of Ionic

Liquids: Springer; 2003.

175. Dalko PI, Moisan L. Enantioselective Organocatalysis. Angewandte Chemie

International Edition. 2001;40(20):3726-3748.

176. Schreiner PR. Metal-free organocatalysis through explicit hydrogen bonding

interactions. Chemical Society Reviews. 2003;32(5):289-296.

177. Welton T. Ionic liquids in catalysis. Coordination Chemistry Reviews.

2004;248(21–24):2459-2477.

178. Olivier-Bourbigou H, Magna L. Ionic liquids: perspectives for organic and

catalytic reactions. Journal of Molecular Catalysis A: Chemical. 2002;182–

183:419-437.

179. Ingold CK. Structure and mechanism in organic chemistry. Vol 1950. 2 ed.

Ithaca, N.Y.: Cornell University Press Ithaca; 1969.

180. Rogers RD, Seddon KR. Ionic Liquids III A: Fundamentals, Progress,

Challenges, and Opportunities Properties and Structure. Washington:

American Chemical Society; 2005.

181. Rogers RD, Seddon KR. Ionic Liquids III B: Fundamentals, Progress,

Challenges, and Opportunities Transformations and Processes. Washington:

American Chemical Society; 2005.

Chapter 1

60

182. Wilkes JS. Properties of ionic liquid solvents for catalysis. Journal of

Molecular Catalysis A: Chemical. 2004;214(1):11-17.

183. Imao D, Fujihara S, Yamamoto T, Ohta T, Ito Y. Effective reductive

amination of carbonyl compounds with hydrogen catalyzed by iridium

complex in organic solvent and in ionic liquid. Tetrahedron.

2005;61(29):6988-6992.

184. Hagiwara H, Okabe T, Hoshi T, Suzuki T. Catalytic asymmetric 1,4-conjugate

addition of unmodified aldehyde in ionic liquid. Journal of Molecular

Catalysis A: Chemical. 2004;214(1):167-174.

185. Basavaiah D, Rao AJ, Satyanarayana T. Recent Advances in the

Baylis−Hillman Reaction and Applications. Chemical Reviews.

2003;103(3):811-892.

186. Hsu J-C, Yen Y-H, Chu Y-H. Baylis–Hillman reaction in [bdmim][PF6] ionic

liquid. Tetrahedron Letters. 2004;45(24):4673-4676.

187. Machado MY, Dorta R. Synthesis and characterization of chiral imidazolium

salts. Synthesis. 2005(15):2473-2475.

188. Abuabdoun I. Photoinitiated cationic polymerization by imidazolium salts.

Abst. Pap. Am. Chem. Soc. 1989;198:96.

189. Cornils B, Herrmann WA. Concepts in homogeneous catalysis: the industrial

view. Journal of Catalysis. 2003;216(1):23-31.

190. Ota E. Some aromatic reactions using AlCl3-rich molten salts. Journal of The

Electrochemical Society. 1987;134:C512.

191. Nemeth LT, Bricker JC, Holmgren JS, Monson LE. Direct carbonylation of

paraffins using an ionic liquid catalyst. US Patent. 2001:628828.

192. Earle MJ, Katdare SP. Oxidative halogenation of aromatic compounds in the

presence of an ionic liquid. World Patent. 2002:WO 2002030852.

193. Earle MJ, Katdare SP. Oxidation of alkylaromatics in the presence of ionic

liquids. World Patent. 2002:WO 2002030862.

194. Earle MJ, Katdare SP. Aromatic nitration reactions in ionic liquids. World

Patent. 2002:WO 2002030865.

Chapter 1

61

195. Earle MJ, Katdare SP. Aromatic sulfonation reactions conducted in the

presence of ionic liquids. World Patent. 2002:WO 2002030878.

196. Morland R. American Chemical Society Division of Industrial and

Engineering Chemistry. Paper presented at: Proceedings of the 221st

American Chemical Society National Meeting2001; San Diego.

197. Suarez PAZ, Dullius JEL, Einloft S, De Souza RF, Dupont J. The use of new

ionic liquids in two-phase catalytic hydrogenation reaction by rhodium

complexes. Polyhedron. 1996;15(7):1217-1219.

198. Suarez PAZ, Dullius JEL, Einloft S, de Souza RF, Dupont J. Two-phase

catalytic hydrogenation of olefins by Ru (II) and Co (II) complexes dissolved

in 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid. Inorganica

chimica acta. 1997;255(1):207-209.

199. Lagrost C, Carrie D, Vaultier M, Hapiot P. Reactivities of some

electrogenerated organic cation radicals in room-temperature ionic liquids:

Toward an alternative to volatile organic solvents? The Journal of Physical

Chemistry A. 2003;107(5):745-752.

200. Janssen MHA, van Rantwijk F, Sheldon RA. Room-temperature ionic liquids

that dissolve carbohydrates in high concentrations. Green Chemistry.

2005;7(1):39-42.

201. Matsumoto M, Mochiduki K, Fukunishi K, Kondo K. Extraction of organic

acids using imidazolium-based ionic liquids and their toxicity to Lactobacillus

rhamnosus. Separation and Purification Technology. 2004;40(1):97-101.

202. Lau RM, Van Rantwijk F, Seddon K, Sheldon R. Lipase-catalyzed reactions in

ionic liquids. Organic Letters. 2000;2(26):4189-4191.

203. Park S, Kazlauskas RJ. Improved preparation and use of room-temperature

ionic liquids in lipase-catalyzed enantio-and regioselective acylations. The

Journal of Organic Chemistry. 2001;66(25):8395-8401.

204. Pfruender H, Jones R, Weuster-Botz D. Water immiscible ionic liquids as

solvents for whole cell biocatalysis. Journal of biotechnology.

2006;124(1):182-190.

Chapter 1

62

205. Kamal A, Chouhan G. A task-specific ionic liquid [bmim]SCN for the

conversion of alkyl halides to alkyl thiocyanates at room temperature.

Tetrahedron Letters. 2005;46(9):1489-1491.

206. Yadav LDS, Patel R, Rai VK, Srivastava VP. An efficient conjugate

hydrothiocyanation of chalcones with a task-specific ionic liquid. Tetrahedron

Letters. 2007;48(44):7793-7795.

207. Kim HS, Kim YJ, Lee H, Park KY, Lee C, Chin CS. Ionic Liquids Containing

Anionic Selenium Species: Applications for the Oxidative Carbonylation of

Aniline. Angewandte Chemie International Edition. 2002;41(22):4300-4303.

208. Fraga-Dubreuil J, Bourahla K, Rahmouni M, Bazureau JP, Hamelin J.

Catalysed esterifications in room temperature ionic liquids with acidic

counteranion as recyclable reaction media. Catalysis Communications.

2002;3(5):185-190.

209. Cole AC, Jensen JL, Ntai I, Tran KLT, Weaver KJ, Forbes DC, Davis JH.

Novel Brønsted Acidic Ionic Liquids and Their Use as Dual

Solvent−Catalysts. Journal of the American Chemical Society.

2002;124(21):5962-5963.

210. Gu Y, Shi F, Deng Y. SO3H-functionalized ionic liquid as efficient, green and

reusable acidic catalyst system for oligomerization of olefins. Catalysis

Communications. 2003;4(11):597-601.

211. Ranu BC, Banerjee S. Ionic Liquid as Catalyst and Reaction Medium. The

Dramatic Influence of a Task-Specific Ionic Liquid, [bmIm]OH, in Michael

Addition of Active Methylene Compounds to Conjugated Ketones, Carboxylic

Esters, and Nitriles. Organic Letters. 2005;7(14):3049-3052.

212. Driver G, Johnson KE. 3-Methylimidazolium bromohydrogenates(i): a room-

temperature ionic liquid for ether cleavage. Green Chemistry. 2003;5(2):163-169.

213. Susan MABH, Noda A, Mitsushima S, Watanabe M. Bronsted acid-base ionic

liquids and their use as new materials for anhydrous proton conductors.

Chemical Communications. 2003(8):938-939.

Chapter 1

63

214. Yoshizawa M, Xu W, Angell CA. Ionic Liquids by Proton Transfer:  Vapor

Pressure, Conductivity, and the Relevance of ∆pKa from Aqueous Solutions.

Journal of the American Chemical Society. 2003;125(50):15411-15419.

215. Mehnert CP, Cook RA, Dispenziere NC, Afeworki M. Supported Ionic Liquid

Catalysis − A New Concept for Homogeneous Hydroformylation Catalysis.

Journal of the American Chemical Society. 2002;124(44):12932-12933.

216. Mehnert CP, Mozeleski EJ, Cook RA. Supported ionic liquid catalysis

investigated for hydrogenation reactions. Chemical Communications.

2002(24):3010-3011.

217. Mehnert CP. Supported Ionic Liquid Catalysis. Chemistry – A European

Journal. 2005;11(1):50-56.

218. Riisager A, Fehrmann R, Haumann M, Wasserscheid P. Supported Ionic

Liquid Phase (SILP) Catalysis: An Innovative Concept for Homogeneous

Catalysis in Continuous Fixed-Bed Reactors. European Journal of Inorganic

Chemistry. 2006;2006(4):695-706.

219. Yamaguchi K, Yoshida C, Uchida S, Mizuno N. Peroxotungstate Immobilized

on Ionic Liquid-Modified Silica as a Heterogeneous Epoxidation Catalyst with

Hydrogen Peroxide. Journal of the American Chemical Society.

2004;127(2):530-531.

220. Dyson PJ, Geldbach TJ. Applications of ionic liquids in synthesis and

catalysis. Interface-Electrochemical Society. 2007;16(1):50-53.

221. Deshmukh RR, Rajagopal R, Srinivasan KV. Ultrasound promoted C-C bond

formation: Heck reaction at ambient conditions in room temperature ionic

liquids. Chemical Communications. 2001(17):1544-1545.

222. Dupont J, Fonseca GS, Umpierre AP, Fichtner PFP, Teixeira SR. Transition-

Metal Nanoparticles in Imidazolium Ionic Liquids:  Recycable Catalysts for

Biphasic Hydrogenation Reactions. Journal of the American Chemical

Society. 2002;124(16):4228-4229.

Chapter 1

64

223. Scheeren CW, Machado G, Dupont J, Fichtner PFP, Texeira SR. Nanoscale

Pt(0) Particles Prepared in Imidazolium Room Temperature Ionic Liquids: 

Synthesis from an Organometallic Precursor, Characterization, and Catalytic

Properties in Hydrogenation Reactions. Inorganic Chemistry.

2003;42(15):4738-4742.

224. Ott LS, Cline ML, Deetlefs M, Seddon KR, Finke RG. Nanoclusters in Ionic

Liquids:  Evidence for N-Heterocyclic Carbene Formation from Imidazolium-

Based Ionic Liquids Detected by 2H NMR. Journal of the American Chemical

Society. 2005;127(16):5758-5759.

225. Mu X, Evans DG, Kou Y. A general method for preparation of PVP-stabilized

noble metal nanoparticles in room temperature ionic liquids. Catalysis Letters.

2004;97(3):151-154.

226. Itoh H, Naka K, Chujo Y. Synthesis of Gold Nanoparticles Modified with

Ionic Liquid Based on the Imidazolium Cation. Journal of the American

Chemical Society. 2004;126(10):3026-3027.

227. Kim KS, Demberelnyamba D, Lee H. Size-selective synthesis of gold and

platinum nanoparticles using novel thiol-functionalized ionic liquids.

Langmuir. 2004;20(3):556-560.

228. Yan N, Zhao C, Luo C, Dyson PJ, Liu H, Kou Y. One-step conversion of

cellobiose to C6-alcohols using a ruthenium nanocluster catalyst. Journal of

the American Chemical Society. 2006;128(27):8714-8715.

229. Zhao D, Fei Z, Ang WH, Dyson PJ. A Strategy for the Synthesis of

Transition‐Metal Nanoparticles and their Transfer between Liquid Phases.

Small. 2006;2(7):879-883.

230. Lancaster NL, Salter PA, Welton T, Young GB. Nucleophilicity in Ionic

Liquids. 2.1 Cation Effects on Halide Nucleophilicity in a Series of

Bis(trifluoromethylsulfonyl)imide Ionic Liquids. The Journal of Organic

Chemistry. 2002;67(25):8855-8861.

231. Holbrey JD, Reichert WM, Nieuwenhuyzen M, Sheppard O, Hardacre C,

Rogers RD. Liquid clathrate formation in ionic liquid–aromatic mixtures.

Chemical Communications. 2003(4):476-477.

Chapter 1

65

232. Grodkowski J, Neta P, Wishart JF. Pulse Radiolysis Study of the Reactions of

Hydrogen Atoms in the Ionic Liquid Methyltributylammonium

Bis[(trifluoromethyl)sulfonyl]imide. The Journal of Physical Chemistry A.

2003;107(46):9794-9799.

233. Bresme F, Alejandre J. Cavities in ionic liquids. The Journal of Chemical

Physics. 2003;118(9):4134-4139.

234. Harper J, Kobrak M. Understanding organic processes in ionic liquids:

Achievements so far and challenges remaining. Mini-Reviews in Organic

Chemistry. 2006;3(3):253-269

235. Lu A-H, Salabas EL, Schüth F. Magnetic Nanoparticles: Synthesis, Protection,

Functionalization, and Application. Angewandte Chemie International

Edition. 2007;46(8):1222-1244.

236. Lu A-H, Salabas EL, Schüth F. Magnetische Nanopartikel: Synthese,

Stabilisierung, Funktionalisierung und Anwendung. Angewandte Chemie.

2007;119(8):1242-1266.

237. Gedanken A. Using sonochemistry for the fabrication of nanomaterials.

Ultrasonics Sonochemistry. 2004;11(2):47-55.

238. Rao CNR, Vivekchand SRC, Biswas K, Govindaraj A. Synthesis of inorganic

nanomaterials. Dalton Transactions. 2007(34):3728-3749.

239. Mastai Y, Gedanken A, Rao CNR, Müller A, Cheetham AK. Chemistry of

Nanomaterials. Vol 1. Weinheim: Wiley-VCH; 2004,.

240. Park J, Joo J, Kwon SG, Jang Y, Hyeon T. Synthesis of Monodisperse

Spherical Nanocrystals. Angewandte Chemie International Edition.

2007;46(25):4630-4660.

241. Park J, Joo J, Kwon SG, Jang Y, Hyeon T. Synthese monodisperser

sphärischer Nanokristalle. Angewandte Chemie. 2007;119(25):4714-4745.

242. Astruc D, Lu F, Aranzaes JR. Nanoparticles as Recyclable Catalysts: The

Frontier between Homogeneous and Heterogeneous Catalysis. Angewandte

Chemie International Edition. 2005;44(48):7852-7872.

Chapter 1

66

243. Astruc D, Lu F, Aranzaes JR. Nanopartikel als regenerierbare Katalysatoren:

an der Nahtstelle zwischen homogener und heterogener Katalyse. Angewandte

Chemie. 2005;117(48):8062-8083.

244. Pan C, Pelzer K, Philippot K, Chaudret B, Dassenoy F, Lecante P, Casanove

M-J. Ligand-Stabilized Ruthenium Nanoparticles:  Synthesis, Organization,

and Dynamics. Journal of the American Chemical Society.

2001;123(31):7584-7593.

245. Aiken JD, Finke RG. Polyoxoanion- and Tetrabutylammonium-Stabilized

Rh(0)n Nanoclusters:  Unprecedented Nanocluster Catalytic Lifetime in

Solution. Journal of the American Chemical Society. 1999;121(38):8803-

8810.

246. Krämer J, Redel E, Thomann R, Janiak C. Use of Ionic Liquids for the

Synthesis of Iron, Ruthenium, and Osmium Nanoparticles from Their Metal

Carbonyl Precursors. Organometallics. 2008;27(9):1976-1978.

247. Ueno K, Tokuda H, Watanabe M. Ionicity in ionic liquids: correlation with

ionic structure and physicochemical properties. Physical Chemistry Chemical

Physics. 2010;12(8):1649-1658.

248. Dupont J, Scholten JD. On the structural and surface properties of transition-

metal nanoparticles in ionic liquids. Chemical Society Reviews.

2010;39(5):1780-1804.

249. Neouze M-A. About the interactions between nanoparticles and imidazolium

moieties: emergence of original hybrid materials. Journal of Materials

Chemistry. 2010;20(43):9593-9607.

250. Consorti CS, Suarez PAZ, de Souza RF, Burrow RA, Farrar DH, Lough AJ,

Loh W, da Silva LHM, Dupont J. Identification of 1,3-Dialkylimidazolium

Salt Supramolecular Aggregates in Solution. The Journal of Physical

Chemistry B. 2005;109(10):4341-4349.

251. Dupont J, Suarez PAZ, De Souza RF, Burrow RA, Kintzinger J-P. C-H-π

Interactions in 1-n-Butyl-3-methylimidazolium Tetraphenylborate Molten

Salt: Solid and Solution Structures. Chemistry – A European Journal.

2000;6(13):2377-2381.

Chapter 1

67

252. Vollmer C, Janiak C. Naked metal nanoparticles from metal carbonyls in ionic

liquids: Easy synthesis and stabilization. Coordination Chemistry Reviews.

2011;255(17):2039-2057.

253. Gannon TJ, Law G, Watson PR, Carmichael AJ, Seddon KR. First

Observation of Molecular Composition and Orientation at the Surface of a

Room-Temperature Ionic Liquid. Langmuir. 1999;15(24):8429-8434.

254. Canongia Lopes JN, Costa Gomes MF, Pádua AAH. Nonpolar, Polar, and

Associating Solutes in Ionic Liquids. The Journal of Physical Chemistry B.

2006;110(34):16816-16818.

255. Law G, Watson PR, Carmichael AJ, Seddon KR. Molecular composition and

orientation at the surface of room-temperature ionic liquids: Effect of molecular

structure. Physical Chemistry Chemical Physics. 2001;3(14):2879-2885.

256. Canongia Lopes JNA, Pádua AAH. Nanostructural Organization in Ionic

Liquids. The Journal of Physical Chemistry B. 2006;110(7):3330-3335.

257. Xiao D, Rajian JR, Cady A, Li S, Bartsch RA, Quitevis EL. Nanostructural

Organization and Anion Effects on the Temperature Dependence of the

Optical Kerr Effect Spectra of Ionic Liquids. The Journal of Physical

Chemistry B. 2007;111(18):4669-4677.

258. Taubert A, Li Z. Inorganic materials from ionic liquids. Dalton Transactions.

2007(7):723-727.

259. Redel E, Thomann R, Janiak C. First Correlation of Nanoparticle Size-

Dependent Formation with the Ionic Liquid Anion Molecular Volume.

Inorganic Chemistry. 2007;47(1):14-16.

260. Gutel T, Garcia-Anton J, Pelzer K, Philippot K, Santini CC, Chauvin Y,

Chaudret B, Basset J-M. Influence of the self-organization of ionic liquids on

the size of ruthenium nanoparticles: effect of the temperature and stirring.

Journal of Materials Chemistry. 2007;17(31):3290-3292.

261. Ott LS, Finke RG. Nanocluster Formation and Stabilization Fundamental

Studies: Investigating “Solvent-Only” Stabilization En Route to Discovering

Stabilization by the Traditionally Weakly Coordinating Anion BF4- Plus High

Dielectric Constant Solvents. Inorganic Chemistry. 2006;45(20):8382-8393.

Chapter 1

68

262. Fonseca GS, Umpierre AP, Fichtner PFP, Teixeira SR, Dupont J. The Use of

Imidazolium Ionic Liquids for the Formation and Stabilization of Ir0 and Rh0

Nanoparticles: Efficient Catalysts for the Hydrogenation of Arenes. Chemistry

– A European Journal. 2003;9(14):3263-3269.

263. Li Z, Friedrich A, Taubert A. Gold microcrystal synthesis via reduction of

HAuCl4 by cellulose in the ionic liquid 1-butyl-3-methyl imidazolium

chloride. Journal of Materials Chemistry. 2008;18(9):1008-1014.

264. Migowski P, Zanchet D, Machado G, Gelesky MA, Teixeira SR, Dupont J.

Nanostructures in ionic liquids: correlation of iridium nanoparticles' size and

shape with imidazolium salts' structural organization and catalytic properties.

Physical Chemistry Chemical Physics. 2010;12(25):6826-6833.

265. Vollmer C, Redel E, Abu-Shandi K, Thomann R, Manyar H, Hardacre C,

Janiak C. Microwave Irradiation for the Facile Synthesis of Transition-Metal

Nanoparticles (NPs) in Ionic Liquids (ILs) from Metal–Carbonyl Precursors

and Ru-, Rh-, and Ir-NP/IL Dispersions as Biphasic Liquid–Liquid

Hydrogenation Nanocatalysts for Cyclohexene. Chemistry – A European

Journal. 2010;16(12):3849-3858.

266. Migowski P, Machado G, Texeira SR, Alves MCM, Morais J, Traverse A,

Dupont J. Synthesis and characterization of nickel nanoparticles dispersed in

imidazolium ionic liquids. Physical Chemistry Chemical Physics.

2007;9(34):4814-4821.

267. Ruta M, Laurenczy G, Dyson PJ, Kiwi-Minsker L. Pd Nanoparticles in a

Supported Ionic Liquid Phase: Highly Stable Catalysts for Selective Acetylene

Hydrogenation under Continuous-Flow Conditions. The Journal of Physical

Chemistry C. 2008;112(46):17814-17819.

268. Anderson K, Cortiñas Fernández S, Hardacre C, Marr PC. Preparation of

nanoparticulate metal catalysts in porous supports using an ionic liquid route;

hydrogenation and C–C coupling. Inorganic Chemistry Communications.

2004;7(1):73-76.

269. Zhu J, Shen Y, Xie A, Qiu L, Zhang Q, Zhang S. Photoinduced Synthesis of

Anisotropic Gold Nanoparticles in Room-Temperature Ionic Liquid. The

Journal of Physical Chemistry C. 2007;111(21):7629-7633.

Chapter 1

69

270. Firestone MA, Dietz ML, Seifert S, Trasobares S, Miller DJ, Zaluzec NJ.

Ionogel-Templated Synthesis and Organization of Anisotropic Gold

Nanoparticles. Small. 2005;1(7):754-760.

271. Safavi A, Maleki N, Tajabadi F, Farjami E. High electrocatalytic effect of

palladium nanoparticle arrays electrodeposited on carbon ionic liquid

electrode. Electrochemistry Communications. 2007;9(8):1963-1968.

272. Redel E, Krämer J, Thomann R, Janiak C. Synthesis of Co, Rh and Ir

nanoparticles from metal carbonyls in ionic liquids and their use as biphasic

liquid–liquid hydrogenation nanocatalysts for cyclohexene. Journal of

Organometallic Chemistry. 2009;694(7–8):1069-1075.

273. Redel E, Thomann R, Janiak C. Use of ionic liquids (ILs) for the IL-anion

size-dependent formation of Cr, Mo and W nanoparticles from metal carbonyl

M(CO)6 precursors. Chemical Communications. 2008(15):1789-1791.

274. Schmid G. Nanoparticles. 2 ed. Weinheim: Wiley-VCH; 2010.

275. Antonietti M, Kuang D, Smarsly B, Zhou Y. Ionic Liquids for the Convenient

Synthesis of Functional Nanoparticles and Other Inorganic Nanostructures.

Angewandte Chemie International Edition. 2004;43(38):4988-4992.

276. Endres F, Bukowski M, Hempelmann R, Natter H. Electrodeposition of

nanocrystalline metals and alloys from ionic liquids. Angewandte Chemie

International Edition. 2003;42(29):3428-3430.

277. Endres F, Bukowski M, Hempelmann R, Natter H. Elektrochemische

Abscheidung nanokristalliner Metalle und Legierungen aus ionischen

Flüssigkeiten. Angewandte Chemie. 2003;115(29):3550-3552.

278. Zhu Y-J, Wang W-W, Qi R-J, Hu X-L. Microwave-Assisted Synthesis of

Single-Crystalline Tellurium Nanorods and Nanowires in Ionic Liquids.

Angewandte Chemie. 2004;116(11):1434-1438.

279. Zhu Y-J, Wang W-W, Qi R-J, Hu X-L. Microwave-Assisted Synthesis of

Single-Crystalline Tellurium Nanorods and Nanowires in Ionic Liquids.

Angewandte Chemie International Edition. 2004;43(11):1410-1414.

Chapter 1

70

280. Silveira ET, Umpierre AP, Rossi LM, Machado G, Morais J, Soares GV,

Baumvol IJR, Teixeira SR, Fichtner PFP, Dupont J. The Partial

Hydrogenation of Benzene to Cyclohexene by Nanoscale Ruthenium Catalysts

in Imidazolium Ionic Liquids. Chemistry – A European Journal.

2004;10(15):3734-3740.

281. Bhatt AI, Mechler A, Martin LL, Bond AM. Synthesis of Ag and Au

nanostructures in an ionic liquid: thermodynamic and kinetic effects

underlying nanoparticle, cluster and nanowire formation. Journal of Materials

Chemistry. 2007;17(21):2241-2250.

282. Kim K-S, Demberelnyamba D, Lee H. Size-Selective Synthesis of Gold and

Platinum Nanoparticles Using Novel Thiol-Functionalized Ionic Liquids.

Langmuir. 2003;20(3):556-560.

283. Shuyan G, Hongjie Z, Xiaomei W, Wenpeng M, Chunyun P, Liaohai G.

Palladium nanowires stabilized by thiol-functionalized ionic liquid: seed-

mediated synthesis and heterogeneous catalyst for Sonogashira coupling

reaction. Nanotechnology. 2005;16(8):1234.

284. Schrekker HS, Gelesky MA, Stracke MP, Schrekker CML, Machado G,

Teixeira SR, Rubim JC, Dupont J. Disclosure of the imidazolium cation

coordination and stabilization mode in ionic liquid stabilized gold(0)

nanoparticles. Journal of Colloid and Interface Science. 2007;316(1):189-195.

285. Zhang H, Cui H. Synthesis and Characterization of Functionalized Ionic

Liquid-Stabilized Metal (Gold and Platinum) Nanoparticles and Metal

Nanoparticle/Carbon Nanotube Hybrids. Langmuir. 2009;25(5):2604-2612.

286. Marcilla R, Mecerreyes D, Odriozola I, Pomposo JA, Rodriguez J, Zalakain

INA, Mondragon INA. New Amine Functional Ionic Liquid as Building Block

in Nanotechnology. Nano. 2007;2(03):169-173.

287. Handy ST, ed Applications of Ionic Liquids in Science and Technology.

Croatia: InTech; 2011.

288. Ott LS, Finke RG. Transition-metal nanocluster stabilization for catalysis: a

critical review of ranking methods and putative stabilizers. Coordination

Chemistry Reviews. 2007;251(9):1075-1100.

Chapter 1

71

289. Migowski P, Dupont J. Catalytic applications of metal nanoparticles in

imidazolium ionic liquids. Chemistry-A European Journal. 2006;13(1):32-39.

290. Moreno-Mañas M, Pleixats R. Formation of carbon-carbon bonds under

catalysis by transition-metal nanoparticles. Accounts of Chemical Research.

2003;36(8):638-643.

291. Knapp R, Wyrzgol SA, Reichelt M, Hammer T, Morgner H, Mu ̈ller TE,

Lercher JA. Corrugated Ionic Liquid Surfaces with Embedded Polymer

Stabilized Platinum Nanoparticles. The Journal of Physical Chemistry C.

2010;114(32):13722-13729.

292. Fedlheim DL, Foss CA. Metal Nanoparticles: Synthesis, Characterization,

and Applications: Taylor & Francis; 2001.

293. Boström M, Williams D, Ninham B. Specific ion effects: why DLVO theory

fails for biology and colloid systems. Physical review letters.

2001;87(16):168103.

294. Cornils B, Herrmann WA, Horváth IT, Leitner W, Mecking S, Olivier-

Bourbigou H, Vogt D. Multiphase Homogeneous Catalysis: Wiley-VCH

Verlag GmbH; 2008.

295. Cole-Hamilton DJ, Tooze RP. Catalyst separation, recovery and recycling:

chemistry and process design: Springer; 2006.

296. Short PL. Out of the ivory tower. Chem. Eng. News. 2006;84(17):15-21.

297. Blanchard LA, Brennecke JF. Recovery of organic products from ionic liquids

using supercritical carbon dioxide. Industrial & Engineering Chemistry

Research. 2001;40(1):287-292.

298. Jastorff B, Molter K, Behrend P, Bottin-Weber U, Filser J, Heimers A,

Ondruschka B, Ranke J, Schaefer M, Schroder H, Stark A, Stepnowski P,

Stock F, Stormann R, Stolte S, Welz-Biermann U, Ziegert S, Thoming J.

Progress in evaluation of risk potential of ionic liquids-basis for an eco-design

of sustainable products. Green Chemistry. 2005;7(5):362-372.

Chapter 1

72

299. Pernak J, Kalewska J, Ksycińska H, Cybulski J. Synthesis and anti-microbial

activities of some pyridinium salts with alkoxymethyl hydrophobic group.

European Journal of Medicinal Chemistry. 2001;36(11–12):899-907.

300. Pernak J, Rogoża J, Mirska I. Synthesis and antimicrobial activities of new

pyridinium and benzimidazolium chlorides. European Journal of Medicinal

Chemistry. 2001;36(4):313-320.

301. Pernak J, Sobaszkiewicz K, Mirska I. Anti-microbial activities of ionic liquids.

Green Chemistry. 2003;5(1):52-56.

302. Pernak J, Chwała P. Synthesis and anti-microbial activities of choline-like

quaternary ammonium chlorides. European Journal of Medicinal Chemistry.

2003;38(11–12):1035-1042.

303. Pernak J, Goc I, Mirska I. Anti-microbial activities of protic ionic liquids with

lactate anion. Green Chemistry. 2004;6(7):323-329.

304. Ranke J, Mölter K, Stock F, Bottin-Weber U, Poczobutt J, Hoffmann J,

Ondruschka B, Filser J, Jastorff B. Biological effects of imidazolium ionic liquids

with varying chain lengths in acute Vibrio fischeri and WST-1 cell viability

assays. Ecotoxicology and Environmental Safety. 2004;58(3):396-404.

305. Lee S-M, Chang W-J, Choi A-R, Koo Y-M. Influence of ionic liquids on the

growth ofEscherichia coli. Korean Journal of Chemical Engineering.

2005;22(5):687-690.

306. Bernot RJ, Brueseke MA, Evans-White MA, Lamberti GA. Acute and chronic

toxicity of imidazolium-based ionic liquids on Daphnia magna. Environmental

Toxicology and Chemistry. 2005;24(1):87-92.

307. Stepnowski P, Skladanowski A, Ludwiczak A, Laczyńska E. Evaluating the

cytotoxicity of ionic liquids using human cell line HeLa. Human &

experimental toxicology. 2004;23(11):513-517.

308. Stolte S, Arning J, Bottin-Weber U, Matzke M, Stock F, Thiele K, Uerdingen

M, Welz-Biermann U, Jastorff B, Ranke J. Anion effects on the cytotoxicity of

ionic liquids. Green Chemistry. 2006;8(7):621-629.