Ionic liquids biphasic systems

Webb, P.B.and Sellin, M.F. and Kimene, T.E. and Williamson, S. and Slawin, A.M.Z. and Cole-Hamilton, D.J. (2003). Continuous Flow Hydroformylation of Alkenes in Supercritical Fluid-Ionic Liquid Biphasic System. J. Am. Chem. Soc., 125, 15577-15588. 

Pina, F. et al.. Thermal and photochemical properties of 4, 7-dihydroxyflavylium in water-ionic liquid biphasic systems a write-read-erase molecular switch, Angew. Chem. Int. Ed., 43,1525,2004. 

Fig. 8.1 Experimental set-up of the recirculating enzymatic membrane reactor used for the synthesis of butyl propionate from vinyl propionate and 1-butanol catalysed by Candida antarctica lipase B in supercritical carbon dioxide and supercritical carbon dioxide/ionic liquid biphasic system [17]...

Supercritical Carbon Dioxide/Ionic Liquid Biphasic System in Enzymatic Synthesis... 

Keeping all these circumstances in mind, it becomes understandable why the use of traditional solvents for biphasic catalysis (e.g., water or butanediol) has only been able to fiilfiU this potential in a few specific examples [41]. Whereas, this type of highly specialized liquid-liquid biphasic operation is an ideal field for the application of ionic liquids, mainly due to their exactly tuneable physicochemical properties (see Section 3.3 for more details). Very recently it has been demonstrated that the solubility and miscibility properties of ionic liquids can be varied so widely that even mutually immiscible ionic liquids can be realized [42], However, applications of these ionic liquid-ionic liquid biphasic systems in catalysis have not yet been described. 

Using ionic liquid biphasic systems means that melts of specially designed, low melting salts are used as one of the liquid phases in combination with an aqueous phase or an immiscible organic solvent... 

The appearance of an offset explains why net photochemistry is observed in the IL, in spite of an efficient back reaction. Fig. 4.7. The chalcone should be preferentially solvated by the [BMIM] organic cation rather than water. As Cc is formed by photoisomerization of Ct, it is either readily converted back to Ct (the back isomerization reaction) or to B2 and AH+. Afterwards, AH in the ionic liquid can be preferentially solvated by the anion and probably by the water molecules present on the water-saturated ionic liquid phase. Therefore, the photochemical production of net AH+ in water/ionic liquids biphasic systems for this chalcone could be explained by the existence of a microheterogeneous structure, where a small fraction of the flavyUum cations would be stabilized by hydrogen bonding and electrostatic interactions with the anions into the polar domains that contain water.[54]... 

Transition metal catalysis in liquid/liquid biphasic systems principally requires sufficient solubility and immobilization of the catalysts in the IL phase relative to the extraction phase. Solubilization of metal ions in ILs can be separated into processes, involving the dissolution of simple metal salts (often through coordination with anions from the ionic liquid) and the dissolution of metal coordination complexes, in which the metal coordination sphere remains intact. 

Finally, a special example of transition metal-catalyzed hydrogenation in which the ionic liquid used does not provide a permanent biphasic reaction system should be mentioned. The hydrogenation of 2-butyne-l,4-diol, reported by Dyson et al., made use of an ionic liquid/water system that underwent a reversible two-... 

Another interesting recent development is the continuous, Rh-catalyzed hydroformylation of 1-octene in the unconventional biphasic system [BMIM][PF6]/scC02, described by Cole-Hamilton et al. [84]. This specific example is described in more detail, together with other recent work in ionic liquid/scC02 systems, in Section 5.4. 

To be applied industrially, performances must be superior to those of existing catalytic systems (activity, regioselectivity, and recyclability). The use of ionic liquid biphasic technology for nickel-catalyzed olefin dimerization proved to be successful. 

To date, several reports have been published dealing with the non-stereoselec-tive hydrogenation of olefins in a liquid-liquid biphasic system containing ionic liquids [69-72]. 

The hydrogenation of arenes is industrially important, but so far has been dominated by the use of heterogeneous catalysts. In principle, ionic liquids offer the chance to use a liquid-liquid biphasic system where the homogeneous catalyst is immobilized and the ionic catalyst solution is reusable. 

A comparison of hydrogenation activity in a biphasic ionic liquid-containing system and a homogeneous media was carried out by Dupont et al. [99]. These authors used a [RuC12-(S)-BINAP]2 NEt3 catalyst precursor dissolved in [BMIM][BF4]. This... 

A butoxylcarbonylation reaction was conducted in a liquid-liquid biphasic system under process conditions, but the removal of the product was conducted in a liquid-solid biphasic system at a lower temperature (84). lodobenzene or 4-bromoacetophenone reacted with CO at a pressure of 1-8 atm in the presence of a palladium-benzothiazole complex catalyst in the ionic liquid [TBA]Br (m.p. = 110°C) in the presence of Et3N base. The catalyst/ionic liquid system was recycled by extractive removal of the butyl ester product with diethyl ether. The solid residue, containing the catalyst, [TBA]Br, and Et3N.HBr, remained effective in subsequent carbonylation tests. After each cycle, the yields were still close to the initial value. A slight decrease in yield was attributed to a loss of catalyst during handling. 

An ionic liquid was fully immobilized, rather than merely supported, on the surface of silica through a multiple-step synthesis as shown in Fig. 15 (97). A ligand tri(m-sulfonyl)triphenyl phosphine tris(l-butyl-3-methyl-imidazolium) salt (tppti) was prepared so that the catalyst, formed from dicarbonylacetylacetonate rhodium and the ligand (P/Rh = 10), could be soluble in both [BMIMJBFq and [BMIM]PF6. The supported ionic liquid-catalyst systems showed nearly three times higher rate of reaction (rate constant = 65 min ) that a biphasic system for the hydroformylation of 1-hexene at 100°C and 1500 psi in a batch reactor, but the n/i selectivity was nearly constant the same for the two ( 2.4). Unfortunately, both the supported and the biphasic ionic liquid systems exhibited similar metal leaching behavior. 

More recent conceptual advances in the liquid/liquid biphasic systems include the novel fluorous biphase system (FBS)12-14,70-73 and the use of ionic liquids15-22... 

Chapter 7 addresses another key topic in the context of green chemistry the replacement of traditional, environmentally unattractive organic solvents by greener alternative reaction media such as water, supercritical carbon dioxide, ionic liquids and perfluorous solvents. The use of liquid/liquid biphasic systems provides the additional benefit of facile catalyst recovery and recycling. 

C4C1im][Cg-S04] TPPD-Guanidine 1-Octene 862-892 (2.5-2.9) Halide-free ionic liquid monophasic system, with addition of cyclohexene biphasic high activity reflection of high octane solubility. [30]... 

Figure 4.9 Hydrogenation in a biphasic ionic liquid-scC02 system.

---