Chloride-free ionic liquids

Chloride-free ionic liquid was essential for the high activity the addition of only 5 mol% [BMIM]C1 led to a significant decrease in the yield because of the basicity of [BMIM]C1 (722). Remarkably, this acid-ionic liquid combination could be reused many times for the glycosidations without any loss in efficiency. 

C CpmHBFJ RuCl2(p-cymene)(PT A) Arenes 60 bar, 90 °C chloride-free ionic liquids are important to [35] achieve high TOF catalyst solution can be reused for at least five runs. 

Our initial investigation of glycosylations in an ionic liquid suffered from a lack of reproducibility. We ultimately realized that chloride anions, which are the most likely expected impurity, are detrimental to the glycosylation reaction [14]. In order to prepare a chloride-free ionic liquid, we adopted the procedure shown in Scheme 3.1, with l-hexyl-3-methylimidazolium trifluoromethanesulfonimidide (C mim[NTf2]) as an example. 

In 2002 Mehnert and co-workers were the first to apply SILP-catalysis to Rh-catalysed hydroformylation [74], They described in detail the preparation of a surface modified silica gel with a covalently anchored ionic liquid fragment (Scheme 7.7). The complex N-3-(3-triethoxysilylpropyl)-4,5-dihydroimidazole was reacted with 1-chlorobutane to give the complex l-butyl-3-(3-triethoxysilylpropyl)- 4,5-dihydroimidazolium chloride. The latter was further treated with either sodium tetrafluoroborate or sodium hexafluorophosphate in acetonitrile to introduce the desired anion. In the immobilisation step, pre-treated silica gel was refluxed with a chloroform solution of the functionalised ionic liquid to undergo a condensation reaction giving the modified support material. Treatment of the obtained monolayer of ionic liquid with additional ionic liquid resulted in a multiple layer of free ionic liquid on the support. 

Danielsson et al. [25] have studied the synthesis of PEDOT in ionic liquids that utilize bulky organic anions, l-butyl-3-methylimidazolium diethylene glycol monomethyl ether sulfate and l-butyl-3-methylimidazolium octyl sulfate, the latter of which is a solid at room temperature and thus requires the addition of either monomer or solvent (in this case water) to form a liquid at room temperature. Polymerization in a water-free ionic liquid was only possible in the octyl sulfate species, but the polymerization of EDOT was successful in aqueous solutions of both the ionic liquids (0.1 M). The ionic liquid anions appear to be mobile within the polymer, exchangeable with chloride ions at a polymer/KCl(aq) interface, but it is interesting that when the PEDOT is in aqueous solutions of the ionic liquid, at higher concentrations (0.01-0.1 M) the imidazolium cation can suppress this anion response. The ion mobility in both the ionic liquid and in the polymer film in contact with the solution is significantly increased by addition of water. 

Fig. 2.2-6 Materials corrosion in water-free ionic liquids (iLs) and reference media. (R1 Water with 250 ppm chloride, R2 uninhibited 1 1 water/glycol mixture.)...

R. V. Jayaram, Tetrahedron Lett. 2012, 53, 2277-2279. Choline chloride 2ZnClj ionic liquid an efficient and reusable catalyst for the solvent free Kabachnik-Fields reaction. 

In contrast, in the presence of MBT, a clear plateau is observed in tlry and chloride-free BMIBF4 (Fig. 7, but not in wet and chloride-containing ionic liquid) at potentials about 100 mV above the corrosion potential indicating a layer of corrosion products, which substantially depress the corrosion rate. 

The Ni-catalyzed oligomerization of olefins in ionic liquids requires a careful choice of the ionic liquid s acidity. In basic melts (Table 5.2-2, entry (a)), no dimerization activity is observed. FFere, the basic chloride ions prevent the formation of free coordination sites on the nickel catalyst. In acidic chloroaluminate melts, an oligomerization reaction takes place even in the absence of a nickel catalyst (entry (b)). FFowever, no dimers are produced, but a mixture of different oligomers is... 

To pursue the development of environmentally benign synthesis routes for ionic liquids, the alkylation step (Menschutkin reaction) was investigated by the authors in detail. The preparation of the ionic liquid 1-hexyl-3-methyhmidazohum chloride ([CeMlMJCl) was taken as a representative experiment (Scheme 7.2). The process parameters temperature (T = 70-100°C), solvent (ethanol, xylene, cyclohexane, n-heptane, solvent free), concentration of the N-base (c = 1.6-6.7 M), molar ratio n n = 1 0.5-1 4) and reaction time (f = 10-144 h) were investigated. In addition, the N-base was altered in order to proof the transferability of the reaction parameters. 

Based on the results of these studies it is quite evident that the reaction with ionic liquid as immobilization phase requires a chloride-free catalyst phase in order to achieve any advantage over the reaction with water as the immobilizing phase. 

Free energy of micellization, 24 130 Free enzyme-catalyzed reactions ionic liquids in, 26 897-898 Free fatty acids, 70 802-804, 825-826 removal of, 70 807 as soap bar additives, 22 742-743 Free-flow agents, in sodium chloride (salt), 22 808... 

Abstract The term Lewis acid catalysts generally refers to metal salts like aluminium chloride, titanium chloride and zinc chloride. Their application in asymmetric catalysis can be achieved by the addition of enantiopure ligands to these salts. However, not only metal centers can function as Lewis acids. Compounds containing carbenium, silyl or phosphonium cations display Lewis acid catalytic activity. In addition, hypervalent compounds based on phosphorus and silicon, inherit Lewis acidity. Furthermore, ionic liquids, organic salts with a melting point below 100 °C, have revealed the ability to catalyze a range of reactions either in substoichiometric amount or, if used as the reaction medium, in stoichiometric or even larger quantities. The ionic liquids can often be efficiently recovered. The catalytic activity of the ionic liquid is explained by the Lewis acidic nature of then-cations. This review covers the survey of known classes of metal-free Lewis acids and their application in catalysis. 

A chloride-free catalyst, Fe(BF4)2-6H20, was used for the reaction of P-oxo ester 24a with MVK (41a) in the ionic liquid [bmim][NTf2] [89]. Product 42a was obtained in about the same yield (95%) as for the solvent-free protocol with Fe(C104)3-9H20 (99% yield) (Scheme 8.27). Both protocols with ionic liquids are, however, operationally less simple than the solvent-free methods reported before, because of the use significant amounts of Et20 for workup and purification of the products. 

The electrodeposition of chromium in a mixture of choline chloride and chromium(III) chloride hexahydrate has been reported recently [39]. A dark green, viscous liquid is obtained by mixing choline chloride with chromium(III) chloride hexahydrate and the physical properties of this deep eutectic solvent are characteristic of an ionic liquid. The eutectic composition is found to be 1 2 choline chloride/chromium chloride. From this ionic liquid chromium can be electrode-posited efficiently to yield a crack-free deposit [39]. Addition of LiCl to the choline chloride-CrCl3-6H20 liquid was found to allow the deposition of nanocrystalline black chromium films [40], The use of this ionic liquid might offer an environmentally friendly process for electrodeposition of chromium instead of the current chromic acid-based baths. However, some efforts are still necessary to get shining... 

In eutectic-based ionic liquids, the chloride ions act as strong ligands for the oxidized metal ions, forming a range of chlorometallate anions. The free chloride ions are present in very low concentrations as they are complexed with the Lewis acidic metal ions and so the dissolution of metal ions must lead to a complex series of equilibria such as... 

Figure 2.8 Specific conductivities of protic vs. aprotic ionic liquids, showing matching of concentrated lithium chloride solution conductivity by solvent-free aprotic liquids. Note that at low temperature, the conductivity of protic nitrate in excess nitric acid is higher than that of the aqueous Lid case with the same excess solvent. (From Xu and Angell [17] by permission)...

Zolflgol MA, Khazaei A, Moosavi-Zare AR (2010) Ionic liquid 3-methyl-l-sulfonic acid imidazolium chloride as a novel and highly efficient catalyst for the very rapid synthesis of bis(indolyl)methanes under solvent-free conditions. Org Prep Proced Int 42 95-102... 

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