Imidazole-based ionic liquids

In the following, the reasons for the higher architectural demands are exemplified at two laboratory examples for liquid-liquid Suzuki coupling and imidazol-based ionic liquid synthesis and can only partly be shown in the example of liquid-liquid and gas-liquid processing scale-out. 

An imidazol-based ionic liquid synthesis was carried out under solvent-free conditions, simply bringing the two liquid reactants into contact... 

Green MD, Long TE (2009) Designing imidazole-based ionic liquids and ionic liquid monomers for emerging technologies. J Macromol Sd R, Part C Polym Rev 49 291-314... 

Scheme 8.57 Imidazole-based ionic liquid for the removal of excess benzyl chloride.

The inks are prepared by mixing an epoxy resin (Epon 826 epoxy resin) with dimethyl methyl phosphonate, nanoclay platelets (Cloisite 30b), silicon carbide whiskers (SI-TUFF SC-050), and milled carbon fibers (Dialead K223HM). Further, an imidazole-based ionic liquid is employed as a latent curing agent (Basionics VS03) (31). 

R = imidazole-based ionic liquid moiety) and PMHS/KF to afford ( )-RBu2SnCH= CHCMe20H. ... 

Figure 15.21 Inhibitory effect of imidazole-based ionic liquid on YADH.

In 2002, Leadbeater and Torenius reported the base-catalyzed Michael addition of methyl acrylate to imidazole using ionic liquid-doped toluene as a reaction medium (Scheme 6.133 a) [190], A 75% product yield was obtained after 5 min of microwave irradiation at 200 °C employing equimolar amounts of Michael acceptor/donor and triethylamine base. As for the Diels-Alder reaction studied by the same group (see Scheme 6.91), l-(2-propyl)-3-methylimidazolium hexafluorophosphate (pmimPF6) was the ionic liquid utilized (see Table 4.3). Related microwave-promoted Michael additions studied by Jennings and coworkers involving indoles as heterocyclic amines are shown in Schemes 6.133 b [230] and 6.133 c [268], Here, either lithium bis(trimethylsilyl)amide (LiHMDS) or potassium tert-butoxide (KOtBu) was em-... 

Certain quaternary salts of imidazoles have become important as ionic liquids, in particular salts of l-butyl-3-methylimidazolium (bmim). Preparation of imidazolium-containing ionic liquids, in the desired product ionic liquid as a solvent, is a virtually solvent-free, one-pot process proceeding in good to excellent yields <2003S2626>. There are also microwave-assisted, solvent-free processes for the preparation of imidazolium-based ionic liquids <2001CC643, 2003GC181>. 

Halogen-free phosphorus based ionic liquids can be produced by direct reaction of (1) phosphines with sulphates (2) tertiary phosphines or imidazoles with alkylating agents such as trialkylphosphates, dialkylphosphonates andmonoalkylphosphinates or (3) phosphines with acid (Scheme 7). 

Noda et al. [ 168] reported the details of Bronsted acid-based ionic liquids consisting of a monoprotonic acid and an organic base, in particular solid bis(trifluorometha-nesulfonyl)amide (HTFSI) and solid imidazole (Im) mixed at various molar ratios to form liquid fractions. Studies of the conductivity, H NMR chemical shift, selfdiffusion coefficient, and electrochemical polarization results indicated that, for the Im excess compositions, the proton conductivity increased with an increasing Im molar fraction, with rapid proton-exchange reactions taking place between the protonated Im cation and Im. Proton conduction was found to occur via a combination of Grotthuss- and vehicle-type mechanisms. Recently, Nakamoto [169] reported the... 

By using scCOz instead of toluene as second phase, Pd-leaching could be avoided, even without additional ammoniumphosphine ligand and the TOF and selectivity was increased to 195 h and >98% respectively [253]. In another publication Tkachenko and coworkers demonstrated that the selective taQ-to-tad dimerization of methyl acrylate can also be carried out with very good results in protonated N-butyl-imidazole, [H-BIM][BF4], giving a first example of the versatility of such simple acid-base ionic liquids in continuous catalytic processes [254]. 

Many ionic liquids are based on N,N-dialkylimidazolium cations (BMI) which form salts that exist as liquids at, or below, room temperature. Their properties are also influenced by the nature of the anion e. g. BF T PFg. The C-2(H) in imidazole is fairly labile but the C-4(H) and the C-5(H) are less so. Under microwave-enhanced conditions it is therefore possible to introduce three deuterium atoms (Scheme 13.4). As hydrogen isotope exchange is a reversible reaction this means that the three deuterium atoms can be readily exchanged under microwave irradiation. For storage purpose it might be best to back-exchange the C-2(D) so that the 4,5-[2H2] isotopomer can be safely stored as the solid without any dangers of deuterium loss. The recently... 

The stability of dialkylimidazolium cation-containing ionic liquids can be a problem even at moderate temperatures in the presence of some reagents or catalysts. For example, when CsF and KF were used in the ionic liquid [BMIM]PFg to perform a halogen exchange reaction in an attempt to replace Br from bromo-carbons with F , it was found that alkyl elimination from the [BMIM] cation took place, forming methyl imidazole, 1-butene, 1-fluorobutane, and other unidentified products at 150°C overnight 69). The fluoride ion acted as a base that promotes elimination or substitution processes. 

Much effort has been devoted to finding synthetically useful methods for the palladium-catalyzed aerobic oxidation of alcohols. For a detailed overview the reader is referred to several excellent reviews [163]. The first synthetically useful system was reported in 1998, when Peterson and Larock showed that simple Pd(OAc)2 in combination with NaHC03 as a base in DMSO as solvent catalyzed the aerobic oxidation of primary and secondary allylic and benzylic alcohols to the corresponding aldehydes and ketones, respectively, in fairly good yields [164, 165]. Recently, it was shown that replacing the non-green DMSO by an ionic liquid (imidazole-type) resulted in a three times higher activity of the Pd-catalyst [166]. 

Surprisingly, it is only a very recent recognition that protic ionic liquids can serve as proton transfer electrolytes in hydrogen-oxygen fuel cells. A current report from the laboratory of Watanabe [40] describes the performance of a hydrogen electrode utilizing, as the electrolyte, the salt formed by proton transfer from the acid form of f>/i-trifluoromethanesulfonyl imide (HTFSI) to the base imidazole. 

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