IONIC LIQUIDS. J.D. HOLBREY, K.R. SEDDON.pdf

Review

Clean Products and Processes 1 (1999) 223–236 Q Springer-Verlag 1999

Ionic Liquids J.D. Holbrey, K.R. Seddon

223 Abstract Ionic liquids are receiving an upsurge of interest as green solvents; primarily as replacements for conventional media in chemical processes. This review presents an overview of the chemistry that has been developed utilising ionic liquids as either catalyst and/or solvent, with particular emphasis on processes that have been taken beyond the pre-competetive laboratory stage and represent clean industrial technology with significant cost and enviromental benefits.

p.a. However, the Montreal Protocol has resulted in a compelling need to re-evaluate many chemical processes that have proved otherwise satisfactory for much of this century. There are four main alternate strategies: 1. solvent-fr solvent-free ee synthesis synthesis,, 2. the use use of water water as as a solvent, solvent, 3. the use of supercri supercritical tical fluids fluids as solvents, solvents, and and 4. the use of ionic ionic liquids liquids as solvents solvents.. It is the purpose of this review to explore option (4), to allow it to be evaluated against the other strategies, and to demonstrate its viability for commercial developIntroduction So what are ionic liquids, and what have they to do with ment in all sectors of the chemical industry. green chemistry? The answer to the first question has As discussed elsewhere recently, (Chauvin and Olivierbeen addressed in a number of reviews and articles Bourbigou 1995, Chauvin 1996, Freemantle 1998a, Freerecently (Chauvin and Olivier-Bourbigou 1995, Chauvin mantle 1998b, Freemantle 1999, Hussey 1983, Hussey 1996, Freemantle 1998a, Freemantle 1998b, Freemantle 1988, Seddon 1996, Seddon 1997, Seddon 1998), the past 1999, Hussey 1983, Hussey 1988, Seddon 1996, Seddon fifty years have seen the melting point of ionic liquids 1997, Seddon 1998, Welton 1999), and will not be drop from c800 7C to –96 7C – from high-temperature discussed in detail here. The answer to the second quescorrosive environments to low-temperature benign tion will become the main text of this article. Clean tech- solvents. Although the archetypal ionic liquids are the N nology concerns the reduction of waste from an indusbutylpyridinium chloride-aluminium(III) chloride-aluminium(III) chloride, trial chemical process to a minimum: it requires the [N Bupy]Cl-AlCl Bupy]Cl-AlCl 3, and 1-ethyl-3-methylimidazolium chlorethinking and redesign of many current chemical procride-aluminium(III) ride-aluminium(III) chloride, [emim]Cl-AlCl3, systems esses. As defined by Roger Sheldon, the E-factor of a (for phase diagram, diagram, see Fig. 1), the range of available process is the ratio (by weight) of the by-products to the anions and cations has expanded enormously in the past desired product(s) (Sheldon 1993, 1997). decade. Indeed, it is our best estimate that, if binary and The Table illustrates that the ‘dirty’ end of the chemternary mixtures are included (and there are very good ical industry, oil refining and bulk chemicals, is remarkpractical and economic reasons for doing that), there are ably waste conscious: it is the fine chemicals and pharapproximately one trillion (10 18) accessible room tempermaceutical companies who are using inefficient, dirty, ature ionic liquids. processes, albeit on a much smaller scale. Volatile Take, for example, the “standard” cations [ N Bupy] Bupy] organic solvents are the normal media for the industrial and [emim] , (see Fig. 2). If the butyl and and ethyl groups, groups, synthesis of organics (petrochemical and pharmaceutical), respectively, are exchanged for a generic linear alkyl with a current world-wide usage of ca. £ 4,000,00 4,000,000,0 0,000 00 function, R (where RpC H 1; n B I [1, 18]), then a series of cations is generated, all of which can be used as the basis of ionic liquids. But is this just a case of methyl, ethyl, butyl, butyl, futyl? No. Figs. 3 and 4 illustrate illustrate the Received: 14 May 1999 / Accepted: 10 July 1999 significant variation in properties which can be induced by this simple change for the [Rmim][PF 6] and J.D. Holbrey, K.R. Seddon c

c

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The QUILL Centre, The Queen’s University of Belfast Stranmillis Road, Belfast BT9 5AG UK e-mail: J.Holbrey 6qub.ac.uk http://www.ch.qub.ac.uk/staff/personal/krs e-mail: K.Seddon6qub.ac.uk The authors would like to thank the ERDF Technology Development Programme and the QUESTOR Centre (JDH) for financial support, and the EPSRC and Royal Academy of Engineering for the award of a Clean Technology Fellowship (to K.R.S.).

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Tabl Tablee 1. The Sheldon E-Factor (Sheldon 1993, 1997)

Industry

Production / tons pa

E-factor

Oil Refining Bulk Chemicals Fine Chemicals Pharmaceuticals

10 6–10 8 10 4–10 6 10 2–10 4 10 1–10 3

0.1 1–5 5–50 25–100

Clean Products and Processes 1 (1999)

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Fig. Fig. 3. Melting point phase diagram for [Rmim][PF 6] ionic liquids as a function of alkyl chain length n showing the melting transitions from crystalline (closed square) and glassy (open square) materials and the clearing transition (closed circle) of the liquid crystalline (LC) terms Fig. Fig. 1. The experimental phase diagram for the [emim]Cl-AlCl 3 system, showing the formation of a compound, [emim][AlCl 4], with a congruent melting point (Fannin et al. 1984)

-butylpyridinium and 1Fig. Fig. 2. The aromatic heterocyclic N -butylpyridinium ethyl-3-methylimidazolium cations

Fig. Fig. 4. Melting point phase diagram for [Rmim][BF 4] ionic liquids as a function of alkyl chain length n showing the melting transitions from crystalline (closed square) and glassy (open square) materials and the clearing transition (closed circle) of the liquid crystalline terms

[Rmim][BF 4] ionic liquids, with data taken from our own laboratories (Bowlas et al. 1996, Gordon et al. 1998, Holbrey and Seddon 1999). An interesting feature of these phase diagrams is the appearance of liquid crystalline phases with the longer alkyl chains, and this is confirmed when their optical textures are examined examined (see Fig. 5). The crystal crystal structure of [C14-mim][PF6] is illustrated in Figs. 6 and 7. 7. The implications of the existence of these stable phases has still to be explored in terms of stereochemical control of reactions. The wide range of reactions that have been undertaken in low temperature ionic liquid solvents is quite

remarkable. The range is limited simply by imagination and the time required for investigation. The specific and selectable solvent properties are a key feature of ionic liquids as solvents and have been utilised, especially in combination with the catalytic properties of the chloroaluminate(III) ionic liquids, to develop a range of synthetically important catalytic reactions, some of which are being investigated as economically and environmentally viable alternatives to existing industrial processes. Room temperature ionic liquids have developed, in less than 20 years, from an adjunct to the US ’Star Wars’ research on battery electrolytes into an industrial reality as media for catalytic chemical processes.

J.D. Holbrey, K.R. Seddon: Ionic Liquids

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Fig. Fig. 5. The characteristic thermotropic (left) and lyotropic (right) textures displayed by [C 14-mim]Cl

Fig. Fig. 6. Single crystal X-ray structure of [C14-mim][PF6]

Fig. Fig. 7. Packing for [C14mim][PF6] within the crystal, showing the typical layered structure with interdigitated alkyl-chains


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Here, we will describe many of the catalytic processes which use low temperature ionic liquids as reaction media. In a number of indicated cases, these processes have been taken through the development process to a point of industrial commercialisation and represent first generation ionic liquid processes, principally based on chloroaluminate(III) ionic liquids which are currently ready for industrial uptake. Following this line, second generation ionic liquid processes based on other, more benign, ionic liquids are currently under investigation and development in a variety of laboratories around the world. Many of these processes utilise the ability of many ionic liquids to selectively immobilise transition metal catalysts for liquidliquid two-phase catalysis while permitting easy, often trivial, extraction of products. Areas under active study include alkylation reactions, Diels-Alder cyclisations, Heck coupling reactions, hydrogenation, hydroformylation, oligomerisation, dimerisation and polymerisation of olefins, and Friedel-Crafts chemistry. In the remainder of this paper, for the sake of conciseness, the term “ionic liquid” should, in general, be taken to mean “ambient, or close-to-ambient, temperature ionic liquid” containing organic cations in contrast to the high temperature simple molten salts, such as NaCl-AlCl 3. Many of the processes discussed (in this terminology, first generation ) make use of the chloroaluminate(III) ionic liquids described above, in the acidic régime (that is, above above 50 mol% AlCl AlCl3). Here, the ionic liquids contain both [AlCl4] – and [Al2Cl7] – anions, and unsurprisingly have been used as substitutes for conventional solid or suspended sources of aluminium(III) chloride. However, ionic liquids, in ideal cases, have no waste associated with them, whereas supported aluminium(III) chloride catalysts involve large (and annually rising) waste disposal costs, and a very “dirty” process. This review is conveniently separated into reactions of alkenes and reactions of arenes with only a relatively small amount of overlap (for instance in the section on linear alkylbenzene production, which is the reaction of an alkene with an arene!).

separation of products from the catalyst is a major problem and leads to increased operational costs and environmental impact. Chauvin and coworkers at the IFP in France (Chauvin et al. 1988, 1990a, 1990b, 1994, 1995a, 1997, Einloft et al. 1996, Olivier et al. 1992) reasoned that chloroaluminate ionic liquids would be good solvents for the nickel catalyst, and discovered that by using a ternary ionic liquid system ([bmim]Cl-AlCl3-EtAlCl2) (bmimpIbutyl-3-methylimidazolium), it is possible to form the active catalyst from a NiCl2L2 precursor and that most importantly, the ionic liquid solvent stabilises the active nickel species. Using the ionic liquid catalyst, the Dimersol reaction can be performed as a two-phase liquid-liquid process at atmospheric pressure at between –15 7C and 5 7C. Under these conditions, alkenes are dimerised with activities well in excess of that found in both solvent-free and conventional solvent systems. The products of the reaction are not soluble in the ionic liquid, and form a second less-dense phase that can be easily separated. The nickel catalyst remains selectively dissolved in the ionic liquid phase, which permits both simple extraction of pure products and efficient recycling of the liquid catalyst phase. In addition to the ease of product/catalyst separation, the key benefits from using the ionic liquid solvent are the increased activity of the catalyst ( 1 250 250 kg of of propene dimerised dimerised per 1 g of Ni catalyst), better selectivity to desirable dimers (rather than higher oligomers), and the efficient use of valuable catalysts through simple recycling of the ionic liquid. This process, using the ionic liquid solvent system, has recently been commercialised by the IFP, as the Difasol process. In this process butene is dimerised in a continuous two-phase procedure with high conversion of olefin and high selectivity to the dimer. Most importantly, the Difasol system can be retro-fitted into existing Dimersol plants to give improved yields, lower catalyst consumption and associated cost and environmental benefits.

Oligomerisation of butene In addition to the nickel-catalysed Difasol processes developed by the IFP, it has been know for some time that acidic ionic liquids themselves act as catalysts for the dimerisation and oligomerisation of olefins, all be it, in a Reactions of Alkenes somewhat uncontrolled manner (Boon et al. 1986). Developments in our laboratories, in collaboration The Dimersol/Difasol process The Dimersol process developed by the IFP (Commereuc with BP Chemicals, have shown that a wide range of et al. 1982) is widely used industrially for the dimerisaacidic chloroaluminate(III) chloroaluminate(III) and alkylchloroaluminate(III) alkylchloroaluminate(III) tion of alkenes, typically propene and butenes, to the ionic liquids catalyse the dimerisation and oligomerisamore valuable branched hexenes and octenes, with tion of olefins (Abdul-Sada et al. 1995a, 1995b, Ambler et twenty-five plants in operation world-wide producing ca. al. 1996). In what is an exceptionally simple system, the 3!10 6 tonnes per annum. The C8 olefins produced are olefinic feedstock may be mixed with, or simply bubbled usually hydroformylated to C9 alcohols for use in the through, the ionic liquid catalyst to produce oligomeric manufacture of plasticisers. The dimerisation process is products which have low solubility in the ionic liquid commonly operated solvent-free with the active catalyst, catalyst and separate as a less dense organic phase which a cationic nickel complex of the general form is readily removed by tapping off. Alternatively, in a [LNiCH2R’][AlCl 4] (where L is PR3). The catalyst has batch process (more commonly used for laboratory been found to be soluble in aromatic and halogenated testing), the ionic liquid is injected into a charged autohydrocarbon solvents, and shows greater catalytic activity clave batch reactor reactor (see Fig. 8): again product product extraction in solution. Although this process is used widely, the amounts to simply tapping off the reactor.


Fig. Fig. 8. An ionic liquid autoclave rig from our laboratories, used for testing batch reactions

In addition to simple oligomerisation reactions, chloroaluminate(III) roaluminate(III) and alkylchloroaluminate(III) alkylchloroaluminate(III) ionic liquids are particularly good catalysts for the polymerisation of olefins. For example, isobutene can be polymerised in an acidic ionic liquid to poly(isobutene) with a higher molecular weight than is formed using other polymerisation processes (Ambler et al. 1996). The catalytic activity of the ionic liquids increases towards higher degrees of polymerisation from short-chain oligomers as the alkylchain length of the 1-alkyl-3-methylimidazolium or N -alkylpyridinium -alkylpyridinium cation is increased, which provides a very effective mechanism for controlling the product distribution of this process from oligomers to polymers. Poly(isobutene), traditionally prepared by the Cosden process, is a valuable lubricant, and also a route to higher value-added materials. The ionic liquid polymerisation process has a number of significant advantages over the industrial Cosden process, which uses a supported or liquid phase aluminium(III) chloride catalyst (Weissermel and Arpe 1997). Using the ionic liquid process, the polymer forms a separate layer, which is substantially free of catalyst and ionic liquid solvent. This is readily removed by tapping off, and the absence of chloroaluminate(III) contamination in the polymer removes the need for a subsequent aqueous washing stage to remove the catalyst. The fact that the polymer is insoluble in the ionic liquid greatly enhances the degree of control available to reduce undesirable secondary reactions (i.e. isomerisations) without requiring alkali quenching of the reaction. A secondary benefit, in common with the Difasol process, is that the separation of the products from the ionic liquid reaction system and elimination of aqueous washing steps enables the reuse rather than destruction of the catalyst, which further reduces costs and wastage from the process. This ionic liquid reaction system can be easily retrofitted to existing Cosden processes, providing a continuous catalytic process with the elimination of costly aqueous washing steps and associated destruction of the catalyst.

Ziegler-Natta Polymerisation Ziegler-Natta polymerisation of ethylene to linear a olefins currently has a world capacity in excess of 1.6!10 6 tonnes per year. The most common production methods involve the use of triethylaluminium catalysts at ca. 100 7C and 100 atmospheres pressure. Other more modern processes can utilise organometallic transition metal catalysts, typically nickel- or titanium-based, for example, using a mixed alkylchloroaluminium(III) and titanium(III) chloride catalyst in an organic solvent to -olefins. Ziegler-Natta polyproduce exceptionally pure a -olefins. merisation of ethylene has been reported in an ionic liquid solvent (Carlin and Wilkes 1990). Using dichlorobis(h 5-cyclopentadienyl)titanium(IV) with an alkyl-chloroaluminium(III) co-catalyst in an acidic [emim]Cl-AlCl 3 ionic liquid solvent, ethylene polymerisation was reported. In comparison, analogous zirconium and hafnium complexes failed to show catalytic activity. Hydrodimerisation of dienes The commercially important hydrodimerisation of 1,3butadiene to octa-2,7-dien-1-ol (Dullius et al. 1998, Silva et al. 1998) has been demonstrated using palladium-based catalysts in [bmim][BF4], a neutral, non-acidic ionic liquid. The ionic liquid, in this case acts purely as a reaction solvent. The catalyst precursor [Pd(mim)2Cl2] was prepared in situ from an imidazolium tetrachloropalladate(II) salt, [bmim]2[PdCl4], dissolved in the ionic liquid solvent. The reaction proceeds in a liquid-liquid twophase system, the products separate from the catalytic reaction mixture as a separate layer on cooling, and are removed by decantation. The cyclo-dimerisation of dienes via Diels-Alder mechanisms have been reported, and are covered in a later section (see below). Alkylation of olefins Olefin alkylation is important as a route to produce branched iso-alkenes. Of particular importance has been the production of 2,3-dimethylbutene, which could be then converted to a methoxy-ether for use as a fuel additive to increase the octane rating. This has been achieved using ionic liquid solvents at the IFP with a modification to the dimersol/difasol process (changing the bulkiness of the phosphine ligands on the nickel catalyst to favour formation of the desirable 2,3-dimethylbutenes from propene) to optimise for high octane number fuel additives (Chauvin et al. 1995a). One of the advantages of an ionic liquid catalyst for this reaction over conventional liquid acid catalysts is that the catalytic activity can be controlled by adjusting the concentration of the active catalyst ([Al2Cl7] –). Using highly acidic ionic liquids, described for olefin oligomerisations, it is possible to alkylate isobutane (Abdul-Sada et al. 1995b, Ambler et al. 1996, Chauvin et al. 1989) at low temperatures (–30–c50 7C) with C2-C4 olefins. This is a reaction that is not effective using normal liquid acidic catalysts (HF and H2SO4). These two ionic liquid based routes to optimised 2,3dimethylbutene production from respectively propylene and ethylene are very good homogeneous processes to

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ionic liquids are often generically referred to as non-chloroaluminates, though clearly this description is derived from an immature view of the breadth of ionic liquid development, since ionic liquids containing chloroalumiDiels-Alder reactions nate Ionic liquids have been demonstrated as effective solvents anions comprise only one of many possible anion for Diels-Alder reactions (Jaeger and Tucker 1989, Earle types. More useful, is the consideration of neutral ionic et al., 1999, Fischer et al., 1999) and show significant rate liquids (in terms of Franklin acidity), in which the anion enhancements, enhancements, high yields and selectivities (see Fig. 9) exists as only a single species, in contrast to the equilicomparable with the best results obtained in convenbrium seen in the tetrachloroaluminate(III) systems: tional solvents. To date, the biggest developments in 2[AlCl4] – a [Al2Cl7] –cCl – Diels-Alder chemistry have come through reactions in Li[ClO4]-Et2O, where the high electrolyte concentrations Since these ionic liquids can not support the existence are cited as beneficial through “salt-effects” and the high internal pressure of the solvent. It is clear from the of reactive Lewis acid conjugate anions (such as [Al2Cl7] – studies cited that extending this concept through to the i.e. there is no analogous mechanism to support use of ionic liquid solvents will lead to further extensions 2[BF4] – a [B2F7] –cF –), they are much less reactive and in the scope of these reactions and eliminate the need for can be used as “innocent” solvents. Under these condipotentially explosive perchlorate-based reaction media. tions, many conventional transition metal catalysts can Also, Chauvin (Chauvin and Olivier-Bourbigou 1995) be utilised. Modification of the ionic liquid solvents reports that “Fe(NO)2” catalysts for the dimerisation of allows the potential to immobilise catalysts, stabilising butadiene to 4–vinylcyclohexene are effective in weakly the active species and to optimise reactant/product solucoordinating [bmim][AF6] (ApP or Sb) ionic liquids. bilities to permit facile extraction of products. The effect of solvent on the reaction rates in moving Hydrogenation of olefins catalysed by transition metal from conventional molecular solvents such as toluene complexes dissolved in ionic liquid solvents have been and THF (Huchette et al. 1978) to the ionic liquid is reported using rhodium- (Suarez et al. 1996), and rutheexceptional. nium- and cobalt-containing catalysts (Suarez et al. 1997). Hydrogenation rates have been shown to be up to five times higher than the comparable reactions in propaHydrogenation and hydroformylation As seen earlier, olefins are very reactive in acidic ionic none, or in analogous two-phase aqueous-organic liquids and dimerisation, polymerisation or oligomerisasystems. The solubilities of the alkene reagents, TOFs, tion reactions readily take place. However, acidic and product distributions are strongly influenced by the [emim]Cl-AlCl3 mixtures are not the only ionic liquids of nature of the anion in the ionic liquid solvent, which can interest. A significant advantage of using ionic liquids as be used to improve the selectivity of the hydrogenation reaction media over traditional molecular solvents is the (Chauvin et al. 1995b). Pentene has been hydrogenated wide range and almost infinite tunability of solvent and using the Osborne rhodium catalyst – [Rh(nbd)(PPh 3)2] catalytic properties. [PF6] (where nbdpnorbornadiene) – in ionic liquids The activity and properties of the liquid can readily be containing [BF4] –, [PF6] –, [SbF6] – and [CuCl2] – anions. controlled by changing composition or by changing the There are significant solvent effects in this reaction; in nature of either the anion or the cations present. In the best case (the [SbF6] – ionic liquid), hydrogenation – neutral ionic liquids containing for example [BF4] , rates were five times higher than the comparable reaction [PF6] –, [SbF6] – and [CuCl2] – anions, the reactive polyin propanone. In contrast, using a chloride-containing merisation and oligomerisation reactions of olefins cataionic liquid as solvent resulted in only isomerisation of lysed by acidic anions are not observed and more pent-1-ene to pent-2-ene, presumably through chloride controlled, specific, reactions can be catalysed. These coordination to the metal-centre deactivating the catalyst. compete with heterogeneous isomerisation and alkylation routes currently used.

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Fig. Fig. 9. Ionic liquids permit high yields and selectivity (endo:exo ratios) for the DielsAlder reaction


Conjugated dienes are more soluble in the ionic liquids than simple olefins, which allows for selective hydrogenation. For example, cyclohexadiene is five times more soluble than cyclohexene in [bmim][SbF6] ionic liquid, and is selectively hydrogenated (98% selectivity, 96% conversion) to cyclohexene, which separates from the ionic liquid. Cyclohexene has also been hydrogenated using Wilkinson’s catalyst – [RhCl(PPh3)3] – or [Rh(cod) 2][BF4] (codp1,4-cyclooctadiene) in ionic liquids containing [BF4] – and [PF6] – anions. -acetamidocinnamic Asymmetric hydrogenations of a -acetamidocinnamic acid (Chauvin et al. 1995b) to (S)-phenylalanine with a cationic chiral rhodium catalyst in [bmim][SbF 6] ionic liquid, and 2-arylacrylic acids (Monteiro et al. 1997) with chiral ruthenium catalysts in [bmim][BF4] ionic liquids, have been reported with a reasonable 64% ee. Palladium catalysts (Carlin and Fuller 1997) immobilised in an ionic liquid-polymer gel membrane (Fuller et al. 1997) containing either [emim][OTf] or [emim][BF4] have also been reported as catalysts for heterogeneous hydrogenation reactions. Hydroformylation (Fuller et al. 1997) of pent-1-ene in [bmim][PF6] with rhodium catalysts shows high catalytic activity; again, the products separate as a second organic phase. It was noted that a small part of the neutral catalyst leached into the organic phase. In general, charged, especially cationic transition metal complexes are most effectively “immobilised” in the ionic liquid solvents. Hydrogenation reactions occur readily using ionic liquids as the catalyst-containing components of a twophase systems. The key feature is that the transition metal catalysts can be immobilised in the polar ionic liquid phase and are not preferentially extracted into organic solvents. The activity may be higher than conventional homogeneous hydrogenations in, for example, propanone or as two-phase aqueous-organic systems where expensive, often synthetically challenging, modified ligands are often required. In the communications described, it is not only demonstrated that hydrogenation reactions occur in neutral (or, more correctly, non-acidic) ionic liquids, but also more generally that many catalytically-active transition metal complexes can be immobilised in ionic liquid solvents without the need for specially modified ligands. The reaction rates and selectivities depend on the relative solubilities of reactants and products in the ionic liquid phase. This is demonstrated by the selective and specific hydrogenation of cyclohexadiene to cyclohexene, and illustrates the potential to tailor reactions by modifying the properties of the ionic liquid solvent.

Miscellaneous reactions of alkenes Alkylammonium and phosphonium salts have been used as solvents for the Heck coupling of aromatic halides with activated olefins using palladium catalysts (Kaufmann et al. 1996): the excess of PPh3 required in conventional solvents is not required to stabilise the palladium catalyst in ionic liquid solvents. Although Heck coupling reactions are not utilised on an industrial scale, and in general produce one equivalent of salt, they are widely used in the pharmaceutical and fine chemical sectors. In

a recent example, the Heck coupling of benzoic acid anhydride with linear a -olefins -olefins has been demonstrated in a process which produces no salt by-products (Stephan et al. 1998) and presents an alternative route to the formation of linear alkylbenzenes (LABs) described later. The benefits of ionic liquid solvents (reactivity, product extraction, etc.) could provide further enhancements to these series of reactions. Nucleophilic aromatic substitution reactions have also been studied in molten dodecyltributylphosphonium salts (Fry and Pienta 1985).

Reactions of Arenes Using the acidic, chloroaluminate(III) ionic liquids as catalytic solvents, aromatic rings show a high reactivity to olefins and undergo a wide range of Lewis acid catalysed chemistry, including clean electrochemical and photochemical polymerisation to form conducting polymeric films, a commercially important alkylation of benzene with olefins, and Friedel-Crafts alkylation and acylation reactions. Formation of poly(p -phenylenes) -phenylenes) Poly( p-phenylenes) have attracted a lot of attention as highly stable conducting polymers for the development of conductive polymeric films and electrolytes (Kovacic and Jones 1987). Polymers can be obtained by polymerisation of benzene using many different chemical methods, but the polymers produced are often of poor quality (contaminated with catalyst and chlorinated and oxygenated residues) and are usually obtained as powders with low relative molecular mass. Electrochemical polymerisation of arenes (Abuabdoun 1989) in acidic chloroaluminate(III) ionic liquids with either N -alkylpyridinium -alkylpyridinium or 1,3–dialkylimidazolium cations has been shown to produce conducting polymers with superior purity, conductivity and greater molecular mass than can be obtained by chemical methods. In addition, electrochemical polymerisation allows the preparation of desirable conducting films. For example, benzene can be electropolymerised to condensed ring conducting polymers (Trivedi 1989), and more importantly, to linear poly( pphenylene) (Arnautov 1997, Kobryanskii and Arnautov 1992b, 1993b) with superior chain lengths. Chemical oxidative polymerisation of benzene to poly( p-phenylenes) (Kobryanskii and Arnautov 1992a, 1993a, 1993c) using [ N -butylpyridinium][AlCl -butylpyridinium][AlCl 4] ionic liquid solvent has also been achieved, the relative molecular mass of the polymers being higher than in conventional solvents. This is attributed to the much higher solubility of the polymer in ionic liquid solvents, which allows extended polymerisation. Electrochemical studies of anthracene (Carlin et al. 1992), methylanthracene (Lee et al. 1996), tetrathiafulvalene (Carter and Osteryoung 1994) and 9,10-anthraquinone (Cheek and Osteryoung 1982, Cheek and Spencer 1994), photoelectrochemical oxidation of aromatic hydrocarbons and decamethylferrocene (Thapar and Rajeshwar 1982), and photochemical oligomerisation of anthracene (Hondrogiannis et al. 1993) have all been reported in ionic liquids. In addition, the synthesis of silane polymer films for electrodes (Carlin and Osteryoung 1994), and

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the electrochemical oxidation and polymerisation of ethylbenzene (Kobryanskii and Arnautov 1993b) have also been reported.

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Reduction of aromatic rings Lewis acid/redox chemistry of 1,2-diarylethanes (Buchanan et al. 1985), hydrogenation of polycyclic aromatics (Buchanan et al. 1981a, 1982), hydride extraction from polycyclic aromatics (Buchanan et al. 1981b, Smith et al. 1980, Zingg et al. 1984), bond cleavage in phenylalkanes (Buchanan et al. 1983), chlorination vs. CC coupling of anthracene radicals (Chapman et al. 1985a, 1985b) and reduction of aromatic ketones (Cheek 1987, 1990, 1991, 1992a, 1992b, Cheek and Herzog 1984a, 1984b) and phenazine and perylene (Coffield et al. 1990, 1991, 1992) have all been reported in the literature using higher temperature ionic liquid systems. No studies have been published concerning room-temperature ionic liquids, but work from our own laboratories (Adams et al. 1999) reports the facile reduction of arenes to cyclic hydrocarbons with a variety of reducing agents: e.g.

Perylene is similarly reduced:

ionic liquids (Ota 1987a, 1987b) (including a one-pot synthesis of anthraquinone from benzene in 94% yield) have been reported. Anthracene undergoes photochemical [4c4] cycloaddition reactions (Hondrogiannis et al. 1993, Pagni et al. 1994) in acidic chloroaluminate(III) ionic liquids. A much wider range of redox products are formed than occur in conventional solvents; the strong Brønsted acidity of the ionic liquid induces protonation of anthracene, by residual traces of HCl, to form an anthracenium species which couples readily via photochemically- driven electron-transfer mechanisms.

Synthesis of linear alkylbenzenes (LABs) The alkylation of arenes with long-chain linear olefins is an example of Friedel-Crafts alkylation which has particular global industrial importance for the synthesis of linear alkylbenzenes (LABs) (Almeida et al. 1994), which are used in the formulation of detergents. The industrial scale of this reaction, coupled with the implications that switching to an ionic liquid process may entail, merits its discussion as a particular example. LAB was first introduced in the 1960s as a precursor to alkylbenzenesulfonates, which are widely used as detergents, and also as emulsifiers, wetting agents, drycleaning additives, lubricants and greases. The global market for LAB is in excess of 2.5!10 6 tonnes per year. Although LABs are produced by alkylation of benzene with chloroalkane feeds, the principal industrial processes for the formation of LAB are alkylation of benzene with do decene over liquid HF or AlCl3 catalysts. A fixed-bed heterogeneous non-corrosive acid catalyst system (Detal from UOP) (Imai et al. 1995) has also recently been introduced. In the liquid acid catalyst processes, especially with HF, the handling of corrosive catalysts leads to increases in the capital cost of the plants and has implications for the disposal of neutralisation products generated within the process. The production of LAB using chloroaluminate(III) ionic liquids as the acid catalyst has been recently described in the patent literature (Abdul-Sada et al. 1995b, Ambler et al. 1996, Lacroix et al. 1998); this is a specific example of the general activation and alkylation with olefins in ionic liquids under acidic conditions. The application of an acidic ionic liquid catalyst as a direct replacement for solid AlCl3 promises significant improvement in the reaction selectivity combined with ease of product separation and elimination of catalyst leaching. Again, as with the Difasol process, the potential to retrofit existing plants will lead to massively reduced catalyst consumption and simplify the production process through the elimination of caustic quenching steps associated with catalyst leaching.

Friedel-Crafts chemistry The Franklin acidic chloroaluminate(III) ionic liquids (containing X (AlCl (AlCl3) 1 0.5) are very aggressive solvents – Both of these reduction sequences is stepwise, each most organic materials are dissolved at high concentraisomer representing a thermodynamic minimum. tions. However, the acidic nature of the solvent causes Electophilic substitution (Skrzynecki-Cooke and ready reaction of the solutes usually via hydride abstracLander 1987) and other reactions of naphthalenes (alkylation reactions leading to oligomerisation or isomerisation, acylation, condensation and migration) in acidic tion, and Friedel-Crafts alkylation or acylation reactions.


Although several Friedel-Crafts reactions have been covered in isolation in earlier sections (i.e. alkylation of arenes), a generalisation of Friedel-Crafts reactions, catalysed in acidic ionic liquids, warrants further consideration. For a general discussion of Friedel-Crafts chemistry, readers are recommended to look at the ’classic’ text book (Olah 1964). Friedel-Crafts alkylations and acylations are of great commercial importance, although there are considerable problems, especially with misnamed “catalytic” Friedel-Crafts acylation reactions, which are actually stoicheometric, consuming 1 mole of AlCl3 per mole of reactant. The nett result is massive usage of aluminium(III) chloride and associated problems with disposal of salt and oxide by-products. Typically, FriedelCrafts alkylation and acylation reactions are run in an inert solvent with suspended or dissolved aluminium(III) chloride as a catalyst, and may take six hours and go only to 80% completion to give a mixture of isomeric products. Both alkylation and acylation reactions under FriedelCrafts conditions have been demonstrated using chloroaluminate(III) ionic liquids as both solvent and catalysts (Adams et al. 1998, Boon et al. 1987a, 1987b, 1986, Jones et al. 1985, Levisky et al. 1984, Ota 1987a, 1987b, Piersma and Merchant 1990, Wilkes 1987). Reaction rates are much faster (often essentially instantaneous) with total reagent conversion, and often with surprising specificity to a single product.

actually consume one molar equivalent of AlCl3 through reaction with the acyl acyl group (see Fig. 10). Friedel-Crafts Friedel-Crafts acylation reactions are industrially important, despite the lack of a true catalytic process, and the associated massive consumption of aluminium(III) chloride. Many acylation reactions have been demonstrated in acidic chloroaluminate(III) ionic liquids liquids (Adams et al. 1998, Boon et al. 1986). As with the conventional processes, difficulties remain from the reaction being noncatalytic in aluminium(III) chloride which necessitates destroying the ionic liquid catalyst by quenching with water to extract the products. However, regioselectivity and reaction rates observed from acylation reactions in ionic liquids are equal to the best published results. Friedel-Crafts acylation of benzene is promoted by Franklin acidic chloroaluminate(III) ionic liquids (Boon et al. 1986): as is typical for acylation reactions, selectively monoacylated products are formed through deactivation of the aromatic ring by the first acyl substituent. The acylated products of these reactions show high selectivities to a single isomer: for example toluene, chlorobenzene and anisole are acylated in the 4-position with 98% specificity. Naphthalene is acylated in the 1-position which is the thermodynamically unfavoured product under conventional Friedel-Crafts acylation conditions compared to the derivatisation at the 2-position, the “normal” product (Adams et al. 1998). This apparent reversal of selectivity in the ionic liquid system is because the acylating species is a fully ionised linear acylium ion ([RCO] ), which is small small (see Fig. 11) compared to the (acyl chloride)-AlCl aducts responsible Alkylation 3 The alkylation of benzene with a wide number of alkyl for acylation in conventional systems. The acylium ion is halides in acidic chloroaluminate(III) ionic liquids (Boon stable in the ionic liquid and has been crystallised as a et al. 1986) leads to rapid and largely uncontrolled salt from a chloroaluminate(III) ionic liquid. However, so polyalkylation with evolution of hydrogen chloride. For far the greatest problems with Friedel-Crafts acylations, example, the alkylation of benzene with chloromethane in namely the non-catalytic reactivity with respect to AlCl 3 an acidic ionic liquid gives a mixture of mono- to hexahas not been adequately addressed. In addition to substituted products. The ionic liquid solvent/catalyst benzene and other simple aromatic rings, a range of activates the reaction and the alkylation can be organic and organometallic substrates (e.g. ferrocene) performed even at temperatures as low as –20 7C in the (Dyson et al. 1997, Surette et al. 1996) have been acylated ionic liquid solvent. The products have a low solubility in in acidic chloroaluminate(III) ionic liquids. Predomithe ionic liquid and are easily separated. nantly mono-acylated products were prepared in good General organic reactions in low melting chloroalumi- yields. nate ionic liquids have been described (Levisky et al. The reactivity of chloroaluminate(III) ionic liquids is 1983, 1984) including Friedel-Craft alkylations, acylations, such that even coals and other carbonaceous materials chlorinations and nitrations in acidic ionic liquids (Boon can be dissolved and reacted. Coals can be acylated in et al. 1987a, 1987b, 1986, Piersma and Merchant 1990). chloroaluminate(III) ionic liquids under much milder The alkylation of arenes using an olefin (Abdul-Sada conditions than can be used with just AlCl3 as catalyst et al. 1995b, Ambler et al. 1996) rather that alkylhalide (Newman et al. 1987, 1980, 1984). Acylation of coals is has been described for the LAB process. In a typical, used as a primary step in liquifaction and desulfurisation generalised procedure, the reaction is performed between processing. 80–200 7C using 0.5% ionic liquid catalyst. For example, benzene is efficiently alkylated with ethylene to ethylben- Photogalvanic cells zene, which can then be dehydrogenated as a source of Hydrophobic ionic liquids containing triflate and bis{(tristyrene. This forms the basis of a competetive procedure fluoromethyl)sulfonyl}amide fluoromethyl)sulfonyl}amide (bis(triflyl)amide; for alkylation of benzene without using ethyl chloride. [N{SO2CF3}2] –) anions have been used as inert, conducting solvents for solar cells (Bonhôte et al. 1996, Papageorgiou et al. 1996, Bonhôte and Dias 1997). Acylation Classical Friedel-Crafts acylation reactions typically use Conventional solar cell technology utilises either organic AlCl3 “catalysts” for the acylation of arenes with acylchlo- solvents containing dissolved electrolytes or conducting rides. However, these are not truly catalytic reactions and solid electrolytes. Both models present a range of probc

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Fig. Fig. 10 10.. The (Benzoyl chloride)-AlCl3 aduct formed from the reaction between benzoyl chloride and aluminium(III) chloride (Nieuenhuyzen et al., unpublished results)

Fig. Fig. 11 11.. The linear [CH3CO] ion and tetrahedral [AlCl4] – ion, as isolated in the ionic [CH3CO][AlCl4] salt (Le Carpentier and Weiss 1972) c

lems, including difficulty maintaining good interface contacts with solid electrolytes, the volatility of organic solvents which necessitates using sealed cells, electrolyte solubility and problems of incompatability of organic solvents with the epoxy resins used in the cell construction. Conducting polymer electrolytes have been devel-

oped to overcome some of these problems; ionic liquid electrolytes combine the advantages of liquid, solventbased electrolytes with those of polymer-electrolytes. By using ionic liquids as the electrolytes, large electrochemical windows ( 1 4 V), good conductiv conductivity, ity, and thermal stability, are achieved with excellent resistance to


oxidation which is caused by uv-excitation of the TiO2 semiconductor supports. The negligible vapour pressure of the ionic liquids, hydrophobicity and compatability with the epoxy resins used permits simple cell construction. Although difficulties with the viscosity of some of the ionic liquid electrolytes is still a feature, solar cells have been prepared which are especially good under low light intensities with sensitiser turnovers in excess of 50 million.

Miscellaneous reactions A number of investigations of chlorination reactions have been made in Lewis acidic ionic liquids. In 1,3-dialkylimidazolium-chloroaluminate ionic liquids, the imidazolium cation undergoes electrophilic substitution at the C(4) and C(5) positions to yield 1,3–dialkyl-4,5-dichloroimidazolium ionic liquids (Donahue et al. 1985, Lipsztajn and Osteryoung 1984). The dichlorinated ionic liquids do not appear to undergo further chlorination and are excellent solvents for chlorination reactions (Boon et al. 1987a, 1987b, Lipsztajn and Osteryoung 1984, Lipsztajn et al. 1986). The chlorination of anthracene in [SbF 6] – ionic liquids (Chapman et al. 1985a) has been reported, and other conventional Lewis acid catalysts have been used in ionic liquids solvents, for example in a mixed tetraalkylammonium nitrate/CuCl2 mixture, the difficult synthesis of a -chloroketones -chloroketones (Atlamsani and Bregeault 1991) has been achieved. Tetraalkylammonium Tetraalkylammonium and 1,3-dialkylimidazolium bromides have been used as highly regioselective solvents for O-alkylation of b -naphthoxide -naphthoxide (Badri and Brunet 1992). Recent work from our own laboratories has extended this to efficient generalised N - and O-alkylation (Earle et al. 1998) and has made the observation that the ionic liquids mimic the behaviour of dipolar aprotic solvents. Consequently, they can be used as clean replacement solvents for DMF and DMSO in a wide range of reactions. Importantly, the ionic liquids are non-volatile, easy to dry and can be quantitatively recovered at the end of the reaction; the products were easily extracted from the ionic liquid into an organic ether phase. Summary These studies have shown that classical transition-metalcatalysed hydrogenation, hydroformylation, isomerisation, dimerisation and coupling reactions can be performed in ionic liquid solvents. Using conventional solvents, selectivities, TOF and reaction rates are effectively uncontrolled: however by using ionic liquid media for the catalysis, it is possible to have a profound influence on all these factors. A combination of subtle (i.e. changing cation substitution patterns) and gross (anion type) modifications to the ionic liquid solvent can permit very precise tuning of reactions. Ionic liquids have been used as effective solvents and catalysts for clean chemical reactions; as replacements for volatile organic and dipolar aprotic solvents (i.e. DMF, DMSO) and solid acid catalysts in reactions ranging from the laboratory to industrial scale. They provide a medium for clean reactions with minimal waste and efficient product extraction, an area which is currently being

investigated (Huddleston et al. 1998, Blanchard et al. 1999). The future directions for catalytic reactions in ionic liquid solvents clearly rely on screening existing catalysts and a greater depth of understanding of the features influencing the specific solvent properties of the different types of ionic liquids. It is anticipated that combinatorial techniques will have a significant role to play.

References Abdul-Sada AK, Ambler PW, Hodgson PKG, Seddon KR, Stewart NJ (1995a) Ionic liquids. World Patent, WO95/21871 Abdul-Sada AK, Atkins MP, Ellis B, Hodgson PKG, Morgan MLM, Seddon KR (1995b) Alkylation process. World Patent, WO95/21806 Abuabdoun II (1989) Photoinitiated cationic polymerization by imidazolium salts. Abst Papers Am Chem Soc 198:96 Adams CJ, Earle MJ, Roberts G, Seddon KR (1998) FriedelCrafts reactions in room temperature ionic liquids. Chem Commun 2097–2098 Adams CJ, Earle MJ, Seddon KR (1999) Stereoselective hydrogenation reactions in chloroaluminate(III) ionic liquids: a new method for the reduction of aromatic compounds. Chem Commun 1043–1044 Almeida JLG de, Defaux M, Ben-Taarit Y, Naccache C (1994) LAB. J Am Oil Chemists Soc 71:675–694 Ambler PW, Hodgson PKG, Stewart NJ (1996) Butene Polymers. European Patent Application, EP/0558187A Arnautov SA (1997) Electrochemical synthesis of polyphenylene in a new ionic liquid. Synth Metals 84 : 295–296 Atlamsani A, Bregeault JM (1991) Monochlorination of methylalkyl ketones in the presence of phase-transfer agents. New J Chem 15:671–675 Badri M, Brunet JJ (1992) Ionic liquids as solvents for the regioselective O-alkylation of C/O ambident nucleophiles. Tetrahedron Lett 33 : 4435–4438 Blanchard LA, Hancu D, Beckman EJ, Brennecke JF (1999) Green processing using ionic liquids and CO 2. Nature 399 [6 th May]:28–29 Bonhôte P, Dias A-P (1997) Hydrophobic liquid salts, the preparation thereof and their appliction in electrochemistry. US Patent 5683832 Bonhôte P, Dias AP, Papageorgiou N, Kalyanasundaram K, Grätzel M (1996) Hydrophobic, highly conductive ambienttemperature molten-salts. Inorg Chem 35:1168–1178 Boon JA, Lander SW, Levisky JA, Pflug JL, Skrynecki-Cooke LM, Wilkes JS (1987a) Catalysis and reactivity of electrophilic reactions in room temperature chloroaluminate molten salts. In: Mamantov G, Blander M, Hussey CL, Mamantov C, Saboungi ML, Wilkes JS (eds) Joint (Sixth) International Symposium on Molten Salts. The Electrochemical Society, pp 979–99 979–9900 Boon JA, Lander SW, Levisky JA, Pflug JL, Skrzynecki-Cooke LM, Wilkes JS (1987b) Catalysis and reactivity of electrophilic reactions in room-temperature chloroaluminate molten-salts. J Electrochem Soc 134:C510 Boon JA, Levisky JA, Pflug JL, Wilkes JS (1986) Friedel Crafts reactions in ambient-temperature molten-salts. J Org Chem 51:480–483 Bowlas CJ, Bruce DW, Seddon KR (1996) Liquid-crystalline ionic liquids. J Chem Soc, Chem Commun 1625–1626 Buchanan AC, Chapman DM, Smith GP (1985) Redox vs Lewis acid catalysis-the chemistry of 1,2-diarylethanes in SbCl 3-rich molten-salt media. J Org Chem 50:1702–1711 Buchanan AC, Dworkin AS, Brown LL, Smith GP (1981a) Lowtemperature hydrogenation of polycyclic aromatic-hydrocarbons (PAHS) by tetralin in a molten-salt catalyst. Abst Papers Am Chem Soc 182:17

233


234

Buchanan AC, Dworkin AS, Smith GP (1981b) Hydride abstraction from 9,10-dihydroanthracene and 5,12-dihydronaphthacene in an aprotic molten-salt medium. J Org Chem 46:471–473 Buchanan AC, Dworkin AS, Smith GP (1982) Molten-salt catalyzed transfer hydrogenation of polycyclic aromatic-hydrocarbons-selective hydrogenation of anthracene and naphthacene by tetralin in molten antimony-trichloride. J Org Chem 47:603–607 Buchanan AC, Dworkin AS, Smith GP (1983) Molten-salt catalysis-selective bond-cleavage reactions for some a ,v -dipheny-diphenylalkanes in SbCl3 melts. J Am Chem Soc 105:2843–2850 Carlin RT, Fuller J (1997) Ionic liquid-polymer gel catalytic membrane. J Chem Soc, Chem Commun 1345–1346 Carlin RT, Osteryoung RA (1994) A silane-based electroactive film prepared in an imidazolium chloroaluminate molten-salt. J Electrochem Soc 141:1709–1713 Carlin RT, Truelove PC, Osteryoung RA (1992) Electrochemical and spectroscopic study of anthracene in a mixed LewisBrønsted acid ambient-temperature molten-salt system. Electrochim trochim Acta 37 : 2615–2628 2615–2628 Carlin RT, Wilkes JS (1990) Complexation of cp 2MCl2 in a chloroaluminate molten-salt – relevance to homogeneous ZieglerNatta catalysis. J Mol Catal 63:125–129 Carter MT, Osteryoung RA (1994) Heterogeneous and homogeneous electron-transfer reactions of tetrathiafulvalene in ambient-temperature chloraluminate molten-salts. J Electrochem Soc 141: 1713–172 1713–17200 Chapman DC, Smith GP, Buchanan AC, Mamantov G (1985a) Effect of melt composition of the reactions of the anthracene radical cation in SbCl 3-rich melts: chlorination versus arylaryl coupling. In: Saboungi ML, Johnson K, Newman DS, Inman D (eds) The Fifth International Symposium on Molten Salts, The Electrochemical Society, Inc, Las Vegas, USA, pp 498–51 498–5111 Chapman DM, Smith GP, Buchanan AC, Mamantov G (1985b) Effect of melt composition on the reactions of the anthracene radical cation in SbCl 3-rich media. J Electrochem Soc 132:C373 Chauvin Y (1996) Two-phase catalysis in nonaqueous ionic liquids. Actualite Chimique 44–46 Chauvin Y, Commereuc D, Hirschauer A, Hugues F, Saussine L (1988) Process and catalyst for the dimerization or codimerization of olefins. French Patent, FR 2,611,700 Chauvin Y, Commereuc D, Hirschauer A, Hugues F, Saussine L (1989) Process and catalyst for the alkylation of isoparaffins with alkenes. French Patent, FR 2,626,572 Chauvin Y, DiMarco F, Olivier H, Gilbert B (1994) Transitionmetal catalysis in room temperature chloroaluminate molten salts: dimerization of propylene catalyzed by nickel complexes and metathesis of olefins catalyzed by tungsten complexes. In: Hussey CL, Newman DS, Mamantov G, Ito Y (eds) Ninth International Symposium on Molten Salts. The Electrochemical Society, Inc, San Francisco, California USA, pp 617–62 617–6244 Chauvin Y, Einloft S, Olivier H (1995a) Catalytic dimerization of propene by nickel-phosphine complexes in 1-butyl-3methylimidazolium chloride/AlEtxCl3-x (xp0,1) ionic liquids. Ind Eng Chem Res 34:1149–1155 Chauvin Y, Gilbert B, Guibard I (1990a) Catalytic dimerization of alkenes by nickel-complexes in organochloroaluminate molten-salts. J Chem Soc, Chem Commun 1715–1716 Chauvin Y, Gilbert B, Guibard I (1990b) Catalytic dimerization of olefins by nickel complexes in organochloroaluminate molten salts. In: Hussey CL, Flengas SN, Wilkes JS, Ito Y (eds) Seventh International Symposium on Molten Salts. The Electrochemical Society, Montreal, Canada, pp 822–832

Chauvin Y, Mussmann L, Olivier H (1995b) A novel class of versatile solvents for two-phase catalysis: Hydrogenation, isomerization, and hydroformylation of alkenes catalyzed by rhodium complexes in liquid 1,3-dialkylimidazolium salts. Angew Chem Int Ed Engl, Engl, pp 2698–2700 2698–2700 Chauvin Y, Olivier-Bourbigou H (1995) Nonaqueous ionic liquids as reaction solvents. CHEMTECH 25:26–30 Chauvin Y, Olivier H, Wyrvalski CN, Simon LC, de Souza R, Dupont J (1997) Oligomerization of n-butenes catalyzed by nickel complexes dissolved in organochloroaluminate ionic liquids. J Catal 165:275–278 Cheek GT (1987) Electrochemical reduction of aromatic ketones in a room-temperature molten-salt. J Electrochem Soc 134 134 : C 141 Cheek GT (1990) Electrochemical reduction of fluorenone in a room-temperature molten salt. In: Hussey CL, Flengas SN, Wilkes JS, Ito Y (eds) Seventh International Symposium on Molten Salts. The Electrochemical Society, Montreal, Canada, pp 325–33 325–3355 Cheek GT (1991) Electrochemistry of aromatic ketones in a room-temperature molten-salt. Abst Papers Am Chem Soc 202:94 Cheek GT (1992a) Electrochemical reduction of aromatic ketones in a room-temperature molten salt. In: Gale RJ, Blomgren G, Kojima H (eds) Eighth International Molten Salts Symposium. The Electrochemical Society, Inc, St Louis, Missouri Missouri USA, pp 426–437 426–437 Cheek GT (1992b) Electrochemical reduction of aromatic ketones in a room-temperature molten-salt. Abst Papers Am Chem Soc 204:236 Cheek GT, Herzog R (1984a) Electrochemical reduction of carbonyl-compounds in a room-temperature molten-salt system-mechanistic and synthetic aspects. J Electrochem Soc 131:C104 Cheek GT, Herzog RB (1984b) Reduction of aromatic ketones in an aluminium chloride:dialkylimidazolium chloride molten salt system. In: Blander M, Newman DS, Saboungi ML, Mamantov G, Jonhson K (eds) The Fourth International Symposium on Molten Salts. The Electrochemical Society, Inc, San Francisco, Francisco, pp 163–173 163–173 Cheek GT, Osteryoung RA (1982) Electrochemical and spectroscopic studies of 9,10-anthraquinone in a room-temperature molten-salt. J Electrochem Soc 129:2488–2496 Cheek GT, Spencer JA (1994) Proton donor characteristics of a room-temperature molten salt. In: Hussey CL, Newman DS, Mamantov G, Ito Y (eds) Ninth International Symposium on Molten Salts. The Electrochemical Society, Inc, San Francisco, California California USA, pp 426–432 426–432 Coffield JE, Mamantov G, Zingg SP, Smith GP (1990) Reduction of aromatic compounds in basic chloroaluminate melts. In: Hussey CL, Flengas SN, Wilkes JS, Ito Y (eds) Seventh International Symposium on Molten Salts, The Electrochemical Society, Society, Montreal, Canada, Canada, pp 336–355 336–355 Coffield JE, Mamantov G, Zingg SP, Smith GP (1991) Reduction of aromatic-compounds in organic chloroaluminate melts. 1. Phenazine. J Electrochem Soc 138 : 2543–2549 Coffield JE, Mamantov G, Zingg SP, Smith GP, Buchanan AC (1992) Reduction of aromatic-compounds in organic chloroaluminate melts. 2. Perylene. J Electrochem Soc 139:355–359 Commereuc D, Chauvin Y, Leger G, Gaillard J (1982) The Dimersol process for dimerisation of olefins – a chemical approach. Revue de L’Institut Francais du Petrole 37:639–649 Donahue FM, Levisky JA, Reynolds GF, Wilkes JS (1985) Reaction of chlorine with ambient-temperature chloroaluminate molten-salts. J Electrochem Soc 132:C372 Dullius JEL, Suarez PAZ, Einloft S, de Souza RF, Dupont J, Fischer J, DeCian A (1998) Selective catalytic hydrodimerization of 1,3-butadiene by palladium compounds dissolved in ionic liquids. Organometallics 17:815–819


Dyson PJ, Grossel MC, Srinivasan N, Vine T, Welton T, Williams DJ, White AJP, Zigras T (1997) Organometallic Synthesis in ambient temperature chloroaluminate (III) ionic liquids-Ligand exchange reactions of ferrocene. J Chem Soc, Dalton Trans 3465–3469 Earle MJ, McCormac PB, Seddon KR (1998) Regioselective alkylation in ionic liquids. Chem Commun 2245–2246 Earle MJ, McCormac PB, Seddon KR (1999) Diels-Alder reactions in ionic liquids. Green Chem 1:23–25 Einloft S, Dietrich FK, de Souza RF, Dupont J (1996) Selective 2-phase catalytic ethylene dimerization by Ni-II complexes/ AlEtCl2 dissolved in organoaluminate ionic liquids. Polyhedron 15:3257–3259 Fannin AA, Floreani DA, King LA, Landers JS, Piersma BJ, Stech DJ, Vaughn RL, Wilkes JS, Williams JL (1984) Properties of 1,3-dialkylimidazolium chloride aluminium chloride ionic liquids 2. J Phys Chem 88:2614–2627 Fischer T, Sethi T, Welton T, Woolf J (1999) Diels-Alder reactions in room temperature ionic liquids. Tetrahedron Lett 40:793–796 Freemantle M (1998a) Designer solvents – Ionic liquids may boost clean technology development. Chem Eng News 76 [30 th March]:32–37 Freemantle M (1998b) Ionic liquids show promise for clean separation technology. Chem Eng News 76 [24 th August]:12 Freemantle M (1999) Ionic liquids prove increasingly versatile. Chem Eng News 77 [4 th June]:23–24 Fry SE, Pienta NJ (1985) Effects of molten-salts on reactionsnucleophilic aromatic-substitution by halide-ions in molten dodecyltributylphosphonium salts. J Am Chem Soc 107:6399–6400 Fuller J, Breda AC, Carlin RT (1997) Ionic liquid-polymer gel electrolytes. J Electrochem Soc 144:L67-L70 Gordon CM, Holbrey JD, Kennedy A, Seddon KR (1998) Ionic liquid crystals: hexafluorophosphate salts. J Mater Chem 8:2627–2636 Holbrey JD, Seddon KR (1999) The phase behaviour of 1-alkyl3-methylimidazolium tetrafluoroborates: Ionic liquids and ionic liquid crystals. J Chem Soc, Dalton Trans : 2133–2139 Hondrogiannis G, Lee CW, Pagni RM, Mamantov G (1993) Novel photochemical behavior of anthracene in a roomtemperature molten-salt. J Am Chem Soc 115:9828–9829 Huchette D, Thery B, Petit F (1978) Diels-Alder Reactions. J Mol Catal 4:433 Huddleston JG, Willauer HD, Swatloski RP, Visser AE, Rogers RD (1998) Room temperature ionic liquids as novel media for ‘clean’ liquid-liquid extraction. Chem Commun, pp 1765–1766 Hussey CL (1983) Ionic Liquids. Adv Molten Salt Chem 5:185–230 Hussey CL (1988) Room-temperature haloaluminate ionic liquids – novel solvents for transition metal solution chemistry. istry. Pure Appl Chem 60 : 1763–1772 1763–1772 Imai T, Kocal JA, Vora BV (1995) The UOP/CEPSA Detal process. Studies Surface Sci Catal 92:339–342 Jaeger DA, Tucker CE (1989) Diels-Alder reactions in ethylammonium nitrate, a low-melting fused salt. Tetrahedron Lett 30:1785–1788 Jones MB, Bartak DE, Stanley DC (1985) Friedel-Crafts polymerizations in aluminum chloride butylpyridinium chloride molten salts. Abst Papers Am Chem Soc 190: 58 Kaufmann DE, Nouroozian M, Henze H (1996) Molten salts as an efficient medium for palladium catalyzed C-C coupling reactions. Synlett 1091–1093 Kobryanskii VM, Arnautov SA (1992a) Chemical synthesis of polyphenylene in an ionic liquid – the possibility of relative molecular mass regulation. J Chem Soc, Chem Commun, 727–728

Kobryanskii VM, Arnautov SA (1992b) Electrochemical synthesis of poly(para-phenylene) in an ionic liquid. Makromol Makromol Chem 193 : 455–463 455–463 Kobryanskii VM, Arnautov SA (1993a) Chemical synthesis of polyphenylene in an ionic liquid. Synth Metals 55:924–929 Kobryanskii VM, Arnautov SA (1993b) Electrochemical oxidation of ethylbenzene in ionic liquid. Vysokomol Soedin, Ser B 35:B2060–B2063 Kobryanskii VM, Arnautov SA (1993c) Synthesis of poly(pphenylene) in ionic liquid. Vysokomol Soedin, Ser A 35:A611–A614 Kovacic P, Jones MB (1987) Dehydrocoupling of aromatic nuclei by catalyst oxidant systems – poly(para-phenylene). Chem Revs 87:357–379 Lacroix CPM, Talma AG, Greco CC, Sherif FG, Shyu L-J (1998) Linear Alkylbenzene formation using low temperature ionic liquid and long chain alkylation agent. World Patent WO9803454 Le Carpentier JM, Weiss R (1972) Etude de Complexes Acide de Lewis-Halogénure d’Acide. I. Structure Cristalline des Hexachloroantimonate, Tétrachloroaluminate et Tétrachlorogallate de Méthyl Oxocarbonium. Acta Crystallogr, Sect B 28:1421 Lee C, Winston T, Unni A, Pagni RM, Mamantov G (1996) Photoinduced electron-transfer chemistry of 9-methylanthracene-substrate as both electron-donor and acceptor in the presence of the 1-ethyl-3-methylimidazolium ion. J Am Chem Soc 118: 4919–492 4919–49244 Levisky JA, Pflug JL, Wilkes JS (1983) Organic-reactions in low melting chloroaluminate molten-salts. J Electrochem Soc 130:C127 Levisky JA, Pflug JL, Wilkes JS (1984) Organic reactions in low melting chloroaluminate molten salts . In: Blander M, Newman DS, Saboungi ML, Mamantov G, Johnson K (eds) The Fourth International Symposium on Molten Salts. The Electrochemical Society, Inc, San Francisco, Francisco, pp 174–182 Lipsztajn M, Osteryoung RA (1984) Reaction of chloride-ions in low-temperature molten-salts and application to the study of complex ion stoichiometry. Inorg Chem 23:1735–1739 Lipsztajn M, Sahami S, Osteryoung RA (1986) Hydroquinone as a proton donor in ambient-temperature chloroaluminate ionic liquids-reaction with chloride-ion. Inorg Chem 25:549–551 Monteiro AL, Zinn FK, De Souza RF, Dupont J (1997) Asymmetric hydrogenation of 2-arylacrylic acids catalyzed by immobilized Ru-binap complex in 1- n-butyl-3-methylimidazolium tetrafluoroborate molten salt. Tetrahedron Asymmetry 8:177–179 Nieuenhuyzen M, Seddon KR, Travers J (unpublished results) Newman DS, Kinstle TH, Thambo G (1987) The acylation of coal and model coal compounds in room temperature molten salts. In: Mamantov G, Blander M, Hussey CL, Mamantov C, Saboungi ML, Wilkes JS (eds) Joint (Sixth) International Symposium on Molten Salts. The Electrochemical Society, pp 991–100 991–10011 Newman DS, Winans RE, McBeth RL (1980) Reactions of coal and model coal compounds in room temperature molten salt mixtures. In: Mamantov G, Blander M, Smith GP (eds) The Third International Symposium on Molten Salts. The Electrochemical Society, Inc, Inc, Hollywood, Florida, USA, pp 425–438 Newman DS, Winans RE, McBeth RL (1984) Reactions of coal and model coal compounds in room- temperature molten-salt mixtures. J Electrochem Soc 131:1079–1083 Olah, GA (1964) Friedel-Crafts and Related Reactions. John Wiley, New York Olivier H, Chauvin Y, Hirschauer A (1992) Room-temperature molten-salts – both novel catalyst for isobutane alkylation and solvent for catalytic dimerization of alkenes. Abst Papers Am Chem Soc 203:75

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Ota E (1987a) Some aromatic reactions using AlCl 3-rich molten salts . In: Mamantov G, Blander M, Hussey CL, Mamantov C, Saboungi ML, Wilkes JS (eds) Joint (Sixth) International Symposium on Molten Salts. The Electrochemical Society, pp 1002–101 1002–10100 Ota E (1987b) Some aromatic reactions using AlCl 3-rich moltensalts. J Electrochem Soc 134:C512 Pagni RM, Mamantov G, Lee CW, Hondrogannis G (1994) The photochemistry of anthracene and its derivatives in room temperature molten salts . In: Hussey CL, Newman DS, Mamantov G, Ito Y (eds) Ninth International Symposium on Molten Salts. The Electrochemical Society, Inc, San Francisco, California California USA, pp 638–645 638–645 Papageorgiou N, Athanassov Y, Armand M, Bonhôte P, Pettersson H, Azam A, Grätzel M (1996) The performance and stability of ambient-temperature molten-salts for solarcell applications. J Electrochem Soc 143:3099–3108 Piersma BJ, Merchant M (1990) Friedel-Crafts alkylation reactions in a room temperature molten salt. In: Hussey CL, Flengas SN, Wilkes JS, Ito Y (eds) Seventh International Symposium on Molten Salts. The Electrochemical Society, Montreal, Montreal, Canada, pp 805–821 805–821 Seddon KR (1996) Room-temperature ionic liquids: neoteric solvents for clean catalysis. Kinetics and Catalysis 37:693–697 Seddon KR (1997) Ionic liquids for clean technology. J Chemical Tech Biotech 68:351–356 Seddon KR (1998) Ionic liquids for clean technology: an update. In: Wendt H (ed) Molten Salt Forum: Proceedings of the 5 th International Conference on Molten Salt Chemistry and Technology, nology, pp 53–62 Sheldon RA (1993) The role of catalysis in waste minimization. In: Weijnen MPC, Drinkenburg AAH (eds) Precision process technology: perspectives for pollution prevention. Kluwer, Dordrecht, Dordrecht, pp 125–138 125–138 Sheldon RA (1997) Catalysis: the key to waste minimization. J Chemical Chemical Tech Biotech 68 : 381–388 381–388 Silva SM, Suarez PAZ, De Souza RF, Dupont J (1998) Selective linear dimerization of 1,3-butadiene by palladium compounds immobilized into 1-n-butyl-3-methyl imidazolium ionic liquids. liquids. Polymer Bulletin 40 : 401–405 401–405 Skrzynecki-Cooke LM, Lander SW (1987) Aromatic electrophilic substitution-reactions in room-temperature molten-salts. Abst Papers Am Chem Soc 193:72 Smith GP, Buchanan AC, Dworkin AS, Sorlie M, Buchanan MV (1980) Catalytic chemistry and spectroscopic studies of SbCl 3 melts containing polycyclic aromatic hydrocarbons . In: Mamantov G, Blander M, Smith GP (eds) The Third International Symposium on Molten Salts. The Electrochemical Society, Hollywood, Florida, USA, pp 393–407

Stephan MS, Teunissen AJJM, Verzijl GKM, de Vries JG (1998) Heck reactions without salt formation: aromatic carboxylic anhydrides as arylating agents. Angew Chem Int Ed Eng 37:662–664 Suarez PAZ, Dullius JEL, Einloft S, De Souza RF, Dupont J (1996) The use of new ionic liquids in 2-phase catalytichydrogenation reaction by rhodium complexes. Polyhedron 15:1217–1219 Suarez PAZ, Dullius JEL, Einloft S, De Souza RF, Dupont J (1997) Two-phase catalytic hydrogenation of olefins by Ru(II) and Co(II) complexes dissolved in 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid. Inorg Chim Acta 255:207–209 Surette JKD, Green L, Singer RD (1996) 1-Ethyl-3-methylimidazolium halogenoaluminate melts as reaction media for the Friedel-Crafts acylation of ferrocene. J Chem Soc, Chem Commun, Commun, pp 2753–2754 2753–2754 Thapar R, Rajeshwar K (1982) Photo-electrochemical oxidation of aromatic-hydrocarbons and decamethyl ferrocene at the room-temperature molten-salt electrolyte interface. J Electrochem Soc 129:560–565 Trivedi DC (1989) Electrochemical synthesis of condensed ring conductive polymers using an ambient-temperature molten salt. J Chem Soc, Chem Commun, pp 544–545 Weissermel K, Arpe H-J (1997) Industrial Organic Chemistry. VCH, Weinheim, 3rd edition Welton T (1999) Room-temperature ionic liquids. Solvents for synthesis and catalysis. Chem Rev 99:2071–2084 Wilkes JS (1987) Friedel-Crafts reactions in chloroaluminate molten salts. In: Mamantov G, Marassi R (eds) Molten salt chemistry: an introduction and selected applications. D Reichel Publishing Company, Dordrecht, pp 405–416 Zingg SP, Dworkin DS, Sorlie M, Chapman DM, Buchanan AC, Smith GP (1984) Reacivity of anthracene in liquid SbCl 3AlCl3n-(1-butyl)pyridinium chloride mixtures. In: Blander M, Newman DS, Saboungi ML, Mamantov G, Johnson K (eds) The Fourth International Symposium on Molten Salts. The Electrochemical Society, San Francisco, pp 248–264

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