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Ionic Liquids in Green Chemistry • • • • • • What are Ionic liquids (ILs)? Why consider of ILs? The characteristic properties of ionic liquids The synthetic methods Research with ILs Outlook What are ionic liquids? Definition: ------ Quite simply, they are liquids that are composed entirely of ions. In the broad sense, this term includes all the molten salts, for instance, sodium chloride at temperatures higher than 800 oC. What are ionic liquids? ------ Ionic liquids are salts that are liquid at low temperature (<100 oC) which represent a new class of solvents with nonmolecular, ionic character. Room temperature Ionic liquids • Room temperature ionic liquids (RTIL) are salts that are liquid over a wide temperature range, including room temperature. • Variations in cations and anions can produce literally millions of ionic liquids, including chiral, fluorinated, and antibacterial IL. • Large number of possibilities allows for fine-tuning the ionic liquid properties for specific applications The driving forces The problems in the chemical industry with the volatile organic compounds (VOCs) : • toxic and/or hazardous • serious environmental issues, such as atmospheric emissions and contamination of aqueous effluents The driving force in the quest for novel reaction media: • greener processes • recycling homogeneous catalysts What is “green chemistry” ? Recently ionic liquids have often been discussed as promising solvents for “clean processes” and “green chemistry”. These two catchwords means to reduce drastically the amounts of side and coupling products and the solvent and catalyst consumption in chemical processes. Why consider Ionic liquids ? • ILs are environmentally-friendly alternatives to organic solvents for liquid/liquid extractions. Catalysis, separations, and electrochemistry. • ILs will reduce or eliminate the related costs, disposal requirements, and hazards associated with volatile organic compounds (VOCs). • The ability to fine-tune the properties of the IL medium will allow selection of IL to replace specific solvents in a variety of different processes. Important IL Properties • • • • • High ionic conductivity Non-flammable Non-volatile High thermal stability Wide temperature range for liquid phase (- 40 to + 200°C) • Highly solvating, yet non-coordinating • Good solvents for many organic and inorganic materials Great promise • Designability. By combining different anions with cations, it is possible to generate a huge number of different ionic liquids, each with their own specific solvent properties. Some ionic liquids are water soluble, others are not. Some dissolve typical organic solvents, other are not. • They can be functionalized to act as acids, bases or ligands and have the potential to catalyze certain reactions in certain systems. • Ionic liquids are non-volatile, hence they may be used in high vacuum systems and high temperature reactions without the requirement of a pressure vessel to contain the vapors. They are good solvents for a wide range of both inorganic, organic and polymeric materials and unusual combinations of reagents can be brought into same phase. However they do not dissolve glass, polyethylene, or Teflon. High solubility usually implies small reactor volumes in the final process. They are immiscible with a number of organic solvents and provide a non-aqueous, polar alternative for two phase systems, this has been used to effect total catalyst recovery in a number of transition metal catalyzed reactions. Hydrophobic ionic liquids can also be used as immiscible polar phase with water. They are often composed of poorly coordinating ions, so they have the potential to be highly polar non-coordinating solvents, this is particularly important when using transitionmetal based catalysts. Characteristics of RTIL • Choice of cation and anion determine physical properties (e.g. melting point, viscosity, density, water solubility, etc.) • Cations are typically big, bulky, and asymmetric accounting for the low melting points • The anion contributes more to the overall characteristics of the IL and determines the air and water stability • Melting point can be easily changed by structural variation of one of the ions or combining different ions Typical RTIL Cations • Room temperature ionic liquids consist of bulky and asymmetric organic cations such as : Imidazolium ion Pyridium ion Ammonium ion Scheme 1. Important types of cation Phosphonium ion Anions for RTIL •A wide range of anions is employed, from simple halides which inflect high melting points, to inorganic anions such as: Anions: • [PF6]- for moisture stable, water immiscible IL • [BF4]- for moisture stable, but water miscible IL depending on the ratio of ionic liquid: water, system temperature, and alkyl chain length in the cation. • Less common anions include: Triflate [TfO] Nonaflate [NfO] CF3SO2CF3(CF2)3SO2Bis(triflyl)amide [Tf2N] Trifluoroacetate [TA] (CF3SO2)2NCF3CO2Heptafluorobutanoate [HB] CF3(CF2)3CO2- Historical Development • Ethylammonium nitrate, which is liquids at RT was first described in 1914. • In the later 1940s, n-alkylpyridinium chloroaluminates were studied as electrolytes for electroplating aluminum. • The first examples of ionic liquids based on dialkylimidazolium cations were reported in the early 1980s. They contain chloroaluminate anions and proved to be useful catalysts/solvents for FriedelCrafts acylations. • The first example of the new ionic liquids, that currently are receiving so much attention as novel media for homogeneous catalysis, ethylmethylimidazolium tetrafluoroborate was reported in 1992. Ionic liquid synthesis Direct quaternization to form cation ------Alkylation reagents Indirect quaternization to form cation Ionic liquid synthesis General procedures: NR3 Step I Step IIa + R'X [R'R3N]+X- + Lewis acid MXy Step IIb 1. + Metal salt M+[A]- MX (precipition) 2. + Bronsted acid H+[A]- HX (evaporation) 3. Ion exchange resin [R'R3N]+[MXy+1]- [R'R3N]+[A]- Scheme 2. synthesis paths for the preparation of ionic liquids examplified for an ammonium salt. The types of RTILS • organoaluminates • air- and water-stable ionic liquids Organoaluminates • Since the organoaluminate ionic liquids have donor and acceptor patterns, The Lewise acidity can be modulated by the relative amount of the aluminum compound. Acidic or basic IL attainable through varying the concentration of the following species: Al2ClAlCl Cl- = 2 AlCl47 + AlCl3 3 ClAlCl4Al2Cl7Acidic basic neutral N N N N N N Et Me basic Et Me neutral Et Me acidic • Basic haloaluminates preclude solvation and solvolysis of metal ion species Large electrochemical windows for both chloro and bromo ionic liquids. The advantage of this controlled Lewis acid ionic liquids is their use in Ziegler-Natta Type catalytic reactions BUT: moisture sensitive Table 1. Melting Point (Mp) and Viscosity (n ) of 1-Ethyl-3methylimidazolium Chloride/Aluminum Chloride Ionic liquid at different Molar Fractions (x) of the Aluminum Compound x Mp (oC) n (p) Table 1. PH Table 1. Table 1. - 60 basic 0.36 1.59 0.50 0.20 2 neutral 0.66 0.16 - 80 acidic Ambient-Temperature, Air- and Waterstable Ionic liquids • Can be obtained by the substitution of the halide anion of the 1,3- dialkylimidazolium cation by other weekly coordinating anions. • In order to be liquid at room temperature, the cation should preferably be unsymmetrical. The melting point is also influenced by the nature of anion. • Can be used for the immobilization of transitionmetal catalyst precursors in biphase catalysis. • Due to their inherent ionic nature, ionic liquids can effectively stabilize cationic transition-metal special that are known to be more attractive than their neutral analogues. “The melting point is influenced by” the nature of cation and anion Applications •Because of their properties, ionic liquids attract great attention in many fields, including organic chemistry, electrochemistry, physical chemistry, and engineering. 1. as reaction media for synthesis and catalysts 2. in electrochemistry 3. in separation processes 4. as electrolytes in solar cells 5. as lubricants 6. as propellants in small satellites 7. matrixes in MALDI mass spectrometry 8. Applications in other areas Catalysis in ionic liquids ------general considerations potentially attractive media for homogeneous catalysis: • They have essentially no vapour pressure which facilitates product separation by distillation. • They are able to dissolve a wide range of organic, inorganic and organometallic compounds. • The solubility of gases, e.g. H2, CO and O2, is generally good which makes them attractive solvents for catalytic hydrogenations, carbonylations, hydroformylations, and aerobic oxidations. • They are immiscible with some organic solvents, e.g. alkanes, and, hence, can be used in two-phase systems. This gives rise to the possibility of a multiphase reaction procedure with easy isolation and recovery of homogeneous catalysts. • Polarity and hydrophilicity / lipophilicity can be readily adjusted by a suitable choice of cation/anion and ionic liquids have been referred to as ‘designer solvents’. • They are often composed of weakly coordinating anions, e.g. BF4- and PF6- and, hence, have the potential to be highly polar yet non-coordinating solvents. They can be expected, therefore, to have a strong rateenhancing effect on reactions involving cationic intermediates. • Ionic liquids containing chloroaluminate ions are strong Lewis, Franklin and Brønsted acids. Protons present in emimAlCl4 have been shown to be superacidic. Such highly acidic ionic liquids are, nonetheless, easily handled and offer potential as non-volatile replacements for hazardous acids such as HF in several acid-catalysed reactions. •Publications to date show that replacing an organic solvent by an ionic liquid can lead to remarkable improvements in well-known processes. •There are also indications that switching from a normal organic solvent to an ionic liquid can lead to novel and unusual chemical reactivity. This opens up a wide field for future investigations into this new class of solvents in catalytic application. Applications • • • • • • Solvent Properties Transition Metal Catalysed Reaction Carbocation Chemistry Separations Electrochemistry Photochemistry Solvent Properties Diels-Alder reaction Aldol condensation Others Diels-Alder reaction O + OMe cyclopentadiene ionic liquid r.t H + CO2M e H CO2Me methyl acrylate ester exo-form endo-from Ionic liquids Composition (% AlCl3) Time (h) emimCl/(AlCl3)x 48 (basic) 22 4.88 32.3 emimCl/(AlCl3)x 48 (basic) 72 5.25 95 emimCl/(AlCl3)x 51 (acidic) 22 19 53 emimCl/(AlCl3)x 51 (acidic) 72 19 79.4 - 72 4.3 91 bmimBF4 Endo/exo Y. (%) ratio Endo selectivity ----highly polar solvents Increases in the reaction rate Allows water sensitive reagents to be used Simple workup Ionic liquid can be reused Aldol Condensation Aldol I O O hydrogenation NaOH aq. 2 H H solvent,reflux, 3h 1 Aldol II O O O + H NaOH aq. H H solvent,reflux, 3h 3 entry solvent reaction type conv.(%) selectivity (%) 1 2* 3 4** 1 bmimBF4 Aldol I 99 64 2 - 33 2 H2 O Aldol I 100 82 0 - 18 3 emimBF4 Aldol II 100 4 6 69 21 4 bmimBF4 Aldol II 100 3 3 80 14 5 H2 O Aldol II 100 36 0 59 5 Solubility Recent activity with RTIL as solvent • sc-CO2 Stripping after Extraction (J. Brennecke) • Conductive RTIL (P. Bonhote) • Ionic liquid-polymer gel electrolytes (R. Carlin) • Catalytic hydrogenation reaction (J. Dupont) • Electrochemistry in RTIL (C. Hussey) • Butene dimerization (H. Olivier) • Benzene polymerization (B. Osteryong) • Two-phase separations (R. D. Rogers) • Friedel-Crafts; regioselectivie alkyl. (K. seddon) • Organometallic synthesis (T. welton) … This list is not exhaustive Transition Metal Catalyzed Reaction • • • • Hydrogenation Heck reaction Stille reaction Other reactions Hydrogenation reaction OH H2, [RuCl2-(S)-BINAP]2.NEt3 (cat.) i PrOH-bmimBF4, r.t., 20 h O O Dupont et al. OH * P (atm) conv.(%) % e.e 1st use 50 100 78 (S) 2nd use 75 100 84 (S) 3rd use 25 90 79 (S) 4th use 100 95 67 (S) Two phase system Simple workup -------decantation Ionic liquid/catalyst phase can be reused IL in Two-Phase Catalytic Reactions Heck Reaction (1) X Pd(OAc)2 + bmimBr NaOAc, 100 ~ 110 oC, 24h styrene R entry stilbenes R X R conv.(%) 1 I H 100 2 Br CHO 100 3 Br MeCO 79 Polar solvent Expensive Phosphine ligand Less expensive High yields Without phosphine Heck reaction (2) OBu OBu Br OBu + Pd(OAc)2 (2.5 mol%), DPPP(2.75 mol%) + solvent, Et3N, 100 oC, 18h enol ethers Dppp = 1,3-bis(diphenylphosphino)propane entry solvent -form conv.(%) / E/Z 1 toluene 23 46/54 68/32 2 DMSO 100 75/25 79/21 3 bmimBF4 50 >99/1 4* bmimBF4 100 >99/1 High regioselectivity Simple workup -------distillation -form Y.(%) 95 Stille reaction O O I + PdCl2(PhCN)2 (cat.) SnBu3 vinyltributyltin iodocyclohexenone bmimBF4 Ph3As, CuI, 80 oC, 2h Y. (%) 1st use 82 2nd use 78 3rd use 72* Simple workup -------extraction Ionic liquid/catalyst phase can be reused Air and moisture stable Other reactions • Suzuki-Miyaura coupling reaction • Trost-Tsuji coupling • Hydroformylation (biphase) Stabilize catalysts Simple workup Atom economy Carbocation Chemistry • IL containing chloroaluminate anions are strong Lewis acids and if protons are present they are superacidic. •The ionic liquids acts as both a solvent and catalyst for a acid catalysed processes involve cationic intermediates, e,g. carbenium and acylium ions • Friedel-Crafts alkylations and acylations • Arene exchange reactions Friedel-Crafts reaction--acylation O O OMe Cl + anisole • Y 64% in acetonitrile •p-/o- = ratio of 93/7 Cu(OTf)2 OMe bmimBF4 methoxybenzophenone Y. quant. ( p-/o-ratio = 94/4 ) • quantitatively • regioselective Friedel-Crafts reaction--akylations The Friedel-Crafts alkylation of benzene with long chain –olefin catalyzed by chloroaluminate ionic liquids modified by HCl which was attributed to the superacidities of these media, were shown to give higher rates and more favorable product distributions. Arene exchange reactions • IL can function as both catalyst and solvent • In a series of arene exchange reactions on ferrocene, an acidic [bmim]+ chloroaluminate IL was used where [Al2Cl7]- is the active Lewis acid. Reactant Fe Arene Product Yield (%) Benzene Fe(C5H5)(C6H6)+ 53 toluene Fe(C5H5)(C6H5Me)+ 64 napthalene Fe(C5H5)(C10H8)+ 53 • Conventional problems with these reactions (e.g., lower yields with solid arenes) are eliminated. Separations • Witting reaction • Others Witting reaction O PPh3 O bmimBF4 C C Me + PhCHO 60 oC, 2.5 h H Ph HC C C Me + Ph3PO H Y. (%) E/Z (%) 1st use 82 97/3 2nd use 83 6th use 91 • The separation of the product and triphenylphosphine oxide • Extractions • Reuse IL Reduction CHO CH2OH Bu3B (1 eq.) ionic liquid ionic liquid temp. (oC) time (h) Y. (%) bmimBF4 100 16 93 emimBF4 100 16 90 emimPF6 100 16 96 emimPF6 r.t. 48 94 • Lower temperature Fluorination CH2Cl Me F N+ N+ . H Me 2 BF4- F O o N H bmimBF4 / MeOH (1 / 1), 20 C, 3 h solvent cosolvent O + N H N H N-fluoro-N’-(chloromethyl)triethylenediamine bis(tetrafluoroborate) entry Me 1 3-fluorinated 2-oxoindoles 2 Temp.(oC) Time (h) 1 (%) 2 (%) 1 MeCN H2 O r.t. over night 71 small amount 2 bmimBF4 MeOH 20 3 99 - • Short reaction time • High yield Ring opening reaction NHR3 O + R2 R1 R3-NH2 bmimBF4, r.t. NHR3 OH + R1 R1 epoxide R2 R1 entry 1 OH Ph R2 H R3 R2 product Ph Ph Time (h) NHPh OH Y. (%) 5.0 85 6.0 83 NHPh 6.0 89 6.0 85 OH 2 -(CH2)4- Ph NHPh 3 PhOCH2 OH H Ph PhO OH 4 Bu H p-tol Bu NH-p-tol • room temperature, economic •This reactions require a large excess of the amines at elevated temperatures. The high temperature reaction conditions are not only detrimental to certain functional groups but also to the control of regioselectivity. •Subsequently, a variety of activators or promoters such as metal amides, metal triflates and transition metal halides have been developed. However, many of these are often expensive or are needed in stoichiometric amounts, thus limiting their practicality. •In the system using ionic liquids, the reaction proceeds at room temperature to give aminoalcohols in high yield. After the reaction, the product was extracted with ether.The ionic liquid was reused in five runs without any loss of activity. Enzymatic reaction OH oAc O lipase + Ph O bmimBF4, r. t., 3.5 h Ph Y. 44% (>99 % e.e.) • similar yields to those of organic solvent systems Others Electrochemistry • Unique features of chloroaluminate ionic liquids include a large electrochemical window, although these anions are moisture sensitive • Possible applications include low cost and recyclable electrolytes for batteries, photoelectrochemical cells, and electroplating • BF4- and PF6- ionic liquids have been developed as moisture stable electrolytes Other types of ionic liquids As the range of application for ionic liquids increase, the need for ionic liquids with special chemical and physical properties also increases. With this in mind, the term “tastspecific ionic liquid” has been introduced to described ‘designer’ligands prepared for special applications. Other types of ionic liquids: Concluding remarks Future IL research Needs: Comprehensive toxicity data Combinatorial approach to IL development Database of physical properties, chemistries, etc. Comparators for direct comparison of IL and traditional solvents Industrial input into a research Agenda Economic synthetic pathways Wider availability REFERENCES Further information regarding physical properties, chemistry, and uses of ionic liquids: [1] Welton T. Chem . Rev., 1999, 99: 2071. [2] Wasserscheid P, Keim W. Angew Chem. .Int. Ed. Engl., 2000, 39: 3722. [3] Freemantle M. (a) Chem . Eng . News, 2000, 78 (May)15: 37-39; (b) Chem . Eng . News, 2001, 79 (Jan)1: 21-25. [4] Earle M J, Seddon K R. Pure Appl, Chem., 2000, 72 (7): 1391-1398. [5] Chum H L, Koch V N et al. J. Am. Chem, Soc., 1975, 97: 3264 . [6] Wilkes JS et al . Inorg . Chem., 1982, 21: 1236. [7] a) Blanchard L A et al. Nature, 1999, 399: 28; b) Blanchard L A et al. Ind. Egn. Chem. Res., 2001, 40: 287. [8] Chauvin Y, Mumann L, Olivier H. Angew. Chem. Int. Engl., 1995, 34: 2698. [9] Monteiro A L et al. Tetrahedron Asymmetry, 1997, 2: 177-179. [10] Song C E, Roh E J. Chem. Commun., 2000: 837-838. [11] Dullins J E L et al. Organometallics, 1998, 17: 815. [12] Kakfman D E et al. Synlett., 1996: 1091. [13] Mathews C J, Smith P J, Welton T. Chem. Commun., 2000: 1249-1250. [14] Bellefon C de et al . J. Mol . Catal., 1999, 145: 121. [15] Adam C J et al. Chem. Commun., 1998: 2097-2098. [16] Boon J A et al. J. Org. Chem., 1986, 51: 48. [17] Kun Qian, Yonquan Deng. J. Mol. Catal. A: Chem., 2001, 171: 81-84. [18] Surretle J K D, Green L, Singer R D. Chem. Commun., 1996: 2753-2754. [19] Wheeler C et al . Chem. Commun., 2001: 887. [20] Earle M J, McCormac P B, Seddon K R. Chem. Commun, 1998: 2245. [21] Hagiwara R, Ito Y J. Fluorine Chem., 2000, 105: 221. [22] Boularre V L, Gree R. Chem. Commun., 2000: 2195-2196. [23] Gordone L M, McClusky A. Chem. Commun., 1999: 1431-1432. [24] Kanalka G W, Maladi R R. Chem. Commun., 2000: 2191. [25] Fischer F, Sethi A , Welton T et al. Tetranedron letters, 1999, 40: 793-796. [26] Earle M J, McCormac P B, Seddon K R. Gree. Chem., 1999, 1:23-25. [27] Visser A E, Swatloski R P, Reichert W M et al. Chem. Commun., 2001: 135. [28] Lall S I, Mancheno D, Castro S. Chem. Commun., 2000: 2413. Thanks