Water-miscible ionic liquids

When water-miscible ionic liquids are used as solvents, and when the products are partly or totally soluble in these ionic liquids, the addition of polar solvents, such as water, in a separation step after the reaction can make the ionic liquid more hydrophilic and facilitate the separation of the products from the ionic liquid/water mixture (Table 5.3-2, case e). This concept has been developed by Union Carbide for the hydroformylation of higher alkenes catalyzed by Rh-sulfonated phosphine ligand in the N-methylpyrrolidone (NMP)/water system. Thanks to the presence of NMP, the reaction is performed in one homogeneous phase. After the reaction. 

When either the organic solvent or the ionic liquid is used as pure solvent, proper control over the water content, or rather the water activity, is of crucial importance, as a minimum amount is necessary to maintain the enzyme s activity. For ionic liquids, a reaction can be operated at constant water activity by use of the same methods as established for organic solvents [17]. [BMIM][PFg] or [BMIM][(CF3S02)2N], for example, may be used as pure solvents and in biphasic systems. Water-miscible ionic liquids, such as [BMIM][BF4] or [MMIM][MeS04], can be used in the second case. 

Husum et al. found that the hydrolytic activities of P-galactosidase from E. coli and the protease subtilisin in a 50 % aqueous solution of the water-miscible ionic liquid [BMIM][Bp4] were comparable to those in 50 % aqueous solutions of ethanol or acetonitrile (Entry 9) [37]. 

In the synthesis of A-acetyllactosamin from lactose and A-acetylglucosamine with (3-galactosidase (289,290), the addition of 25 vol% of the water-miscible ionic liquid [MMIM][MeS04] to an aqueous system was found to effectively suppress the side reaction of secondary hydrolysis of the desired product. As a result, the product yield was increased from 30 to 60%. Product separation was improved, and the reuse of the enzymatic catalyst became possible. A kinetics investigation showed that the enzyme activity was not influenced by the presence of the ionic liquids. The enzyme was stable under the conditions employed, allowing its repeated use after filtration with a commercially available ultrafiltration membrane. 

When the water-miscible ionic liquid [MMIM][MeS04] was used as a neat medium for the enzymatic transformations, however, poorer performance was observed. For the kinetic resolution of mc-l-phenylethanol by transesterification with vinyl acetate with a set of different lipases dispersed in the pure ionic liquid, it was found that [MMIM][MeS04] was among the poorest media for the enzymes (291). It has been recognized that some water-miscible ionic liquids in the pure form are denaturants (27), but, when they are used in the presence of excess water, their tendency to... 

Tao, W., Pan, D., Liu, Q., Yao, S., Nie, Z., and Han, B., Optical and bioelec-trochemical characterization of water-miscible ionic liquids based composites of multiwalled carbon nanotubes. Electroanalysis, 18,1681-1688,2006. 

Gutowski, K.E., Broker, G.A., Willauer, H.D., Huddelston, R.R, Swatloski, J.D., Holbrey, J.D., Rogers, R.D., Gontrolling the aqueous miscibility of ionic liquids Aqueous biphasic systems of water-miscible ionic liquids and waterstructuring salts for recycle, metathesis and separations, /. Am. Chem. Soc., 125, 6632-6633, 2003. 

Hong ES, Kwon OY, Ryu K (2008) Strong substrate-stabilizing effect of a water-miscible ionic liquid [BMIM][BF4] in the catalysis of horseradish peroxidase. Biotechnol Lett 30 529-533... 

Tao WY, Pan DW, Yao SZ et al (2006) Optical and bioelectrochemical characterization of water-miscible ionic liquids based composites of multiwaUed carbon nanotubes. Electioanalysis 18 1681-1688... 

The preparation of water-miscible ionic liquids can be a more demanding process, as the separation of the desired and undesired salts may be complex. The use of silver salts described above allows the preparation of many salts in very high purity, but is clearly too expensive for large-scale use. As a result, a number of alternative protocols have been developed that employ cheaper salts for the metathesis reaction. The most common approach remains to carry out the exchange in aqueous solution using either the free acid of the appropriate anion, the ammonium salt, or an alkali metal salt. When using this approach, it is important that the desired ionic liquid can be isolated without excess contamination from unwanted halide-... 

Oxidoreductases are of special interest for the enantioselective reduction of prochiral ketones [49]. Formate dehydrogenase from Candida boidinii was found to be stable and active in mixtures of [MMIM][MeS04] with buffer. The apphcation of alcohol dehydrogenases for enzyme-catalyzed reactions in the presence of water-miscible ionic liquids could make use of another advantage of these solvents they increase the solubility of hydrophobic compounds in aqueous systems. By addition... 

Yu, R., Lin, Y, Xiang, L., Su, L., Zhang, J., and Mao, L. (2005). Molecular films of water-miscible Ionic liquids formed on glassy carbon electrodes Characterization and electrochemical applications. Langmuir, 21, pp. 9000-9006. 

In order to look at the effect of water on the structure of both hydrophobic and hydrophilic room-temperature ionic liquids, SFG measurements were taken at water partial pressures of 5 X 10 Torr and 20 Torr. Results showed that ionic liquid behaviour at the surface differed depending on whether the ionic liquid was hydrophobic or hydrophilic. For hydrophobic ionic liquids, the imidazolium ring reorients towards the surface normal upon addition of water, while for hydrophilic ionic liquids, the ring remains flat on the surface. The process was found to be reversible, with the tilting of the cation attributed to the interaction of water with C(2)—H. Moreover, for water-miscible ionic liquids, water molecules were said to be... 

Rivera-Ruber0, S. and Baldelli, S., Influence of water on the surface of the water-miscible ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate A sum frequency generation analysis, J. Phys. Chem. B110,15499-15505 (2006). 

Guo B, Chen F, Lei Y, Liu X, Wan J, Jia D (2009) Styrene-butadiene rubber/halloysite nanotubes nanocomposites modified by sorbic acid. Appl Surf Sci 255(16) 7329-7336 Gutowski KE, Broker GA, Willauer HD, Huddleston JG, Swatloski RP, Holbrey JD, Rogers RD (2003) Controlling the aqueous miscibility of ionic liquids aqueous biphasic systems of water-miscible ionic liquids and water-structuring salts for recycle, metathesis, and separations. J Am Chem Soc 125(22) 6632-6633... 

Zafarani-Moattar MX, Hamzehzadeh S (2010) Salting-out effect, preferential exclusion, and phase separation in aqueous solutions of chaotropic water-miscible ionic liquids and kosmotropic salts effects of temperature, anions, and cations. J Chem Eng Data 55 1598-1610... 

Water-miscible ionic liquids are usually toxic to microorganisms, but some microorganisms tolerate small amounts of water-miscible ionic hquids. For ejomple, Pichia... 

Zabet-Moghaddam et al. ° characterized five different ionic liquids by LDI and by MALDl-MS. Signals of both anions and cations of the ionic liquids could be observed both in LDI- and in MALDI-MS without any metal adducts. Low-molecular-mass compounds and peptides could be analyzed best in the presence of water-immiscible ionic liquids, whereas proteins gave the best results in water-miscible ionic liquids. Optimal analytical conditions depend on the molar ratio of matrix-to-analyte and ionic hquid-to-matrix, although the homogeneity of samples in the presence of ionic liquids was reduced compared with classical MALDl preparations. 

Yu P, Lin Y, Xiang L, Su L, Zhang J, Mao L (2005) Molecular films of water-miscible ionic liquids formed on glassy carbon electrodes characterization and electrochemical applications. Langmuir 21(20) 9000-9006. doi 10.1021/la051089v... 

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