Effects of Ionic Liquids

However, the bromide ion in [BMIM]Br or [TBA]Br has been found to become beneficial when used to stabilize the noble metal catalysts that are prone to form zerovalent nanoparticles, which could agglomerate further under reaction conditions, resulting in the loss of the catalysts 84). 

Heck and C-C coupling reactions (183). The highest activity and stability of palladium was observed in the ionic liquid [BMIM]Br. 

---

Section 3.3. In this section we deal specifically with the electrochemical properties of ionic liquids (electrochemical windows, conductivity, and transport properties) we will discuss the techniques involved in measuring these properties, summarize the relevant literature data, and discuss the effects of ionic liquid components and purity on their electrochemical properties. 

As new compounds, very limited research has been done to evaluate the biological effects of ionic liquids. The topical effect of [EMIM]C1/A1C13 melts and [EMIMjCl on the integument of laboratory rat has been investigated. The study reports that [EMIMjCl is not in itself responsible for tissue damage. However, the chloroaluminate salt can induce tissue irritation, inflammation, and necrosis, due to the presence of aluminium chloride. However, treatments for aluminium chloride and hydrochloric acid are well documented. This study needs to be expanded to the other ionic liquids, and their toxicity need to be investigated [46]. 

Several reports deal also with the effects of ionic liquids on enzyme enantioselectivity, which is the subject of this chapter. Although in several cases there was no change or even a decrease in enantioselectivity compared to organic solvents [47], in other cases improved enantioselectivity was observed [47,49-56]. In the following text, the latter cases will be examined in some detail. 

S. J. Pool and K.H. Shaughnessy. Effects of ionic liquids on oxidative addition to square planar iridium and rhodium complexes. Abstracts of Papers, 231st ACS National Meeting, Atlanta, GA, USA, March 26-30,2006 (2006). 

Chiappe, C., Leandri, E., Hammock, B.D. and Morisseau, C. (2007) Effect of ionic liquids on epoxide hydrolase-catalyzed synthesis of chiral 1,2-diols. Green Chemistry, 2007 (9), 162-168. 

A truly co-catalytic effect of ionic liquids is observed with those ionic liquids displaying a certain latent or real Lewis-acid character. These ionic liquids are usually formed by the reaction of a halide salt with a Lewis acid (e. g. chloroaluminate or chlorostannate melts). In many examples, the Lewis acidity of an ionic liquid has been used to convert the neutral catalyst precursor into the active form of the catalyst by halide abstraction (see Scheme 7.1) [39]. 

Alkylimidazolinm tetraflnoroborates are, for example, ionic liquids at room-temperature that can provide an anion to stabilize an intermediate cation-radical with no possibility of nucleophilic attack on it. Ionic liquids have a huge memory effect, and their total friction is greater than that of conventional polar solvents. Thus, the total friction of l-ethyl-3-methylimidazolium hexafluoro-phosphate is about 50 times greater than that of AN (Shim et al. 2007). The solvent effects of ionic liquids on ion-radical ring closures deserve a special investigation. The ring closure reactions can be, in principal, controlled by solvent effects. 

Polyakova, Y. and Row, K. H., Retention behaviour of N-CBZ-D-phenylalanine and D-tryptophan Effect of ionic liquid as mobile-phase modifier, Acta Chromatogr., 17, 210-221,2006. 

The resolution of chiral alcohols through lipase-mediated enantioselective acylation (transesterification) is one of the major industrial applications of lipases [50]. Hence, the effects of ionic liquid reaction media on the resolution of various... 

The solvent effect of ionic liquids on the decarboxylation of 1,3-dimethylorotic acid and its analogue has been investigated.12 The rate acceleration observed has been attributed to stabilization of the zwitterionic intermediates by the charged groups available in these special solvents. 

Several reports on the effect of ionic liquids on Sn reactions have been published. The rate constants of the Sn2 reactions of several anions with n-hexyl and n-octyl mesylates in two ionic liquids, [hexmim]C104 and [hexmim]PF6 containing 2000 ppm of water, were compared with the reactivity in chlorobenzene, DMSO, and MeOH.74 The results indicated that the relative nucleophilicities in the ionic liquids were similar to those in the other solvents. The rates in the ionic liquids were generally faster than those in MeOH but slower than those in DMSO or chlorobenzene. 

The effect of ionic liquid solvents on the stereochemical selectivity of allylation of 2-methoxycyclohexanone has been investigated, and found a higher selectivity (axial alcohol 34/equatorial alcohol 35) toward the chelation-controlled mechanism in ionic liquid than in conventional solvents such as water and THF. The use of 0.1 equiv. of indium, combined with Mn and TMSC1 (2 equiv. of each), results in the isolation of the desired products in good purity, with an overall conversion of 81% (Scheme 39).168... 

C jimHPFs] Mn(porphyrin) complex PhI(OAc)2 Epoxidation of styrene CH2C12 as co-solvent better results in presence of an ionic liquid effect of ionic liquid concentration and oxidant concentration studied products extracted with hexane catalyst active for at least 10 runs without significant decrease in activity MnTPPS4 is more active than MnTPPCl. [34] [35]... 

In a preliminary study, the effect of ionic liquid-inherent impurities on the peak area A (and hence the vapour pressure) of a solute was investigated using the example of toluene in [C6mim]Cl, to which either water or 1-methylimidazole were deliberately added to simulate the most likely impurities occurring in ionic liquids. 

Welton s group has conducted a huge body of work to elucidate the effect of ionic liquid compositions in nucleophilic reactions. 

DTBP (2,4-di-tert-butylphenol) in ionic liquids. Moreover, the selectivity to 2,4-DTBP was increased from 29.7% to 64.9%. For the HPW/MCM-41-catalyzed alkylation reactions, the improvement in effects of ionic liquids was also observed. 

Here, we will review the various issues related to biocatalytic reactions in ionic liquids. Biocatalyst tested in ionic liquids will be discussed firstly, and then the effect of ionic liquids on the activity, selectivity as well as on the stability of biocatalyst in ionic liquids will be surveyed. Finally, various applications of ionic liquids as reaction medium for biocatalytic transformations will be reviewed. 

Carridn FJ, Sanes J, Bermridez MD (2007) Effect of ionic liquid on the structure and tribological properties of polycarbonate-zinc oxide nanodispersion. Mater Lett 61 4531 535... 

Zhao H, Campbell SM, Jackson Letal (2006) Hofmeister series of ionic liquids kosmotropic effect of ionic liquids on the enzymatic hydrolysis of enantiomeric phenylalanine methyl ester. Tetrahedron Asymmetr 17 377-383... 

An alternative avenue to exploring the polarity of a solvent is by investigating its effect on a chemical reaction. Since the purpose of this book is to review the potential application of ionic liquids in synthesis, the effect of ionic liquids on chemical reactions has been treated separately (see Chapter 5, Section 5.1). 

L. Rehmann, E. Ivanova, J.L. Ferguson et al., Measuring the effect of ionic liquids on laccase activity using a simple, parallel method. Green Chem. 14 (2012) 725-733. 

A.P. de los Rios, F.J. Hernandez-Fernandez, F.A. Martinez et al., The effect of ionic liquid media on activity, selectivity and stability of Candida antarctica lipase B in transesterification reactions. Biocat. Biotrans. 25 (2007) 151-156. 

WUC Wu, C., Wang, J., Pei, Y., Wang, H., and Li, Z., Salting-out effect of ionic liquids on poly(propylene glycol) (PPG) Formation of PPG + ionic liquid aqueous two-phase... 

Welton et al. [127] have used the linear solvation energy relationships (LSERs) approach to study the effects of ionic liquids on the kinetics of various Sfj2 nucleophilic substitution reactions. These take several forms, with different forms of charge distribution behavior (Table 2.1) [90]. 

Reactants Activated complex Effect of ionic liquid on rate... 

Virtanen, P., Karhu, H., Kordas, K., and Mikkola, J.-P. (2007) The effect of ionic liquid in supported ionic liquid catalysts (SILCA) in the hydrogenation of a,p-unsaturated aldehydes. Ghent. Eng. Sci., 62, 3660-3671. 

A.G. (2006) The effect of ionic liquids on product yield and catalyst stability. Chem. Eng. Sd., 61, 1338-1341. 

---