Ambient-temperature ionic liquid

Ambient-temperature ionic liquids have received much attention in both academia and industry, due to their potential as replacements for volatile organic compounds (VOCs) [1-3]. These studies have utilized the ionic liquids as direct replacements for conventional solvents and as a method to immobilize transition metal catalysts in biphasic processes. 

Many organic chemical transformations have been carried out in ionic liquids hydrogenation [4, 5], oxidation [6], epoxidation [7], and hydroformylation [8] reactions, for example. In addition to these processes, numerous synthetic routes involve a carbon-carbon (C-C) bond-forming step. As a result, many C-C bondforming procedures have been studied in ambient-temperature ionic liquids. Among those reported are the Friedel-Crafts acylation [9] and allcylation [10] reactions, allylation reactions [11, 12], the Diels-Alder reaction [13], the Heck reaction [14], and the Suzuld [15] and Trost-Tsuji coupling [16] reactions. 

The first use of ionic liquids in free radical addition polymerization was as an extension to the doping of polymers with simple electrolytes for the preparation of ion-conducting polymers. Several groups have prepared polymers suitable for doping with ambient-temperature ionic liquids, with the aim of producing polymer electrolytes of high ionic conductance. Many of the prepared polymers are related to the ionic liquids employed for example, poly(l-butyl-4-vinylpyridinium bromide) and poly(l-ethyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide [38 1]. 

Noda and Watanabe [42] reported a simple synthetic procedure for the free radical polymerization of vinyl monomers to give conducting polymer electrolyte films. Direct polymerization in the ionic liquid gives transparent, mechanically strong and highly conductive polymer electrolyte films. This was the first time that ambient-temperature ionic liquids had been used as a medium for free radical polymerization of vinyl monomers. The ionic liquids [EMIM][BF4] and [BP][Bp4] (BP is N-butylpyridinium) were used with equimolar amounts of suitable monomers, and polymerization was initiated by prolonged heating (12 hours at 80 °C) with benzoyl... 

The effects of increasing the concentration of initiator (i.e., increased conversion, decreased M , and broader PDi) and of reducing the reaction temperature (i.e., decreased conversion, increased M , and narrower PDi) for the polymerizations in ambient-temperature ionic liquids are the same as observed in conventional solvents. May et al. have reported similar results and in addition used NMR to investigate the stereochemistry of the PMMA produced in [BMIM][PFgj. They found that the stereochemistry was almost identical to that for PMMA produced by free radical polymerization in conventional solvents [43]. The homopolymerization and copolymerization of several other monomers were also reported. Similarly to the findings of Noda and Watanabe, the polymer was in many cases not soluble in the ionic liquid and thus phase-separated [43, 44]. 

The previous sections show that certain ionic liquids, namely the chloroalumi-nate(III) ionic liquids, are capable of acting both as catalyst and as solvent for the polymerization of certain olefins, although in a somewhat uncontrolled manner, and that other ionic liquids, namely the non-chloroaluminate(III) ionic liquids, are capable of acting as solvents for free radical polymerization processes. In attempts to carry out polymerization reactions in a more controlled manner, several studies have used dissolved transition metal catalysts in ambient-temperature ionic liquids and have investigated the compatibility of the catalyst towards a range of polymerization systems. 

Figure 7.4-1 Nickel catalysts used for the polymerization and oligomerization of ethyiene in ambient-temperature ionic liquids [48, 49].

Carmichael, A.J., and Seddon, K.R., Polarity study of some l-alkyl-3-methyl-imidazolium ambient-temperature ionic liquids with the solvatochromatic dye, Nile Red, /. Phys. Org. Chem., 13, 591-595,2000. 

Campbell, J. L. E., Johnson, K. E., and Torkelson, J. R., Infrared and variable-temperature H-NMR investigations of ambient-temperature ionic liquids prepared by reaction of HCl with l-ethyl-3-methyl-lH-imidazolium chloride, Inorg. Chem., 33, 3340,1994. 

Zawodzinski, T. A., Jr., Kurland, R., and Osteryoung, R. A., Relaxation time measurements in N-(l-butyl)pyridinium-alummum chloride ambient temperature ionic liquids, /. Phys. Chem., 91,962,1987. 

Although it is only an arbitrary divide, ionic liquids are generally defined as salts that melt at or below 100 °C to afford liquids composed solely of cations and anions. In some cases the ionic liquids are even free-flowing liquids at room temperature, so-called ambient temperature ionic liquids. Other terms such as molten salts or fused salts are also used, particularly in the older literature. 

The conductivity of ionic liquids can be modeled in the same manner as the viscosity, i.e. despite the high ionic strength of the liquid, ionic migration is limited by the availability of suitably sized voids [130]. Since the fraction of suitably sized holes in ambient temperature ionic liquids is effectively at infinite dilution, migration should be described by a combination of the Stokes-Einstein and Nernst-Einstein equations. This is explained in greater detail in Chapter 11.3 on process scale-up but it is sufficient to say that an expression can be derived for the conductivity, k... 

The preceding chapters have shown that the majority of metals can now be electrodeposited from ambient-temperature ionic liquids. However, this does not necessarily mean that the liquid with the widest potential window will negate the use of all other ionic liquids. Rather, it is most likely that ionic liquids will be task-specific with discrete anions being used for metals that cannot be electrodeposited from aqueous solutions such as Al, Li, Ti, V and W. Type I eutectics will probably be the most suitable for Al, Ga and Ge. Type II eutectics are most suitable for Cr and Type III are most suited to Zn, Cu, Ag and associated alloys. Type III will also find application in metal winning, oxide recycling and electropolishing. To date most practically important metals have been electrodeposited from ionic liquids and a comprehensive review is given in articles by Abbott [99] and Endres [100-102],... 

Palladium-catalyzed Suzuki cross-coupling reactions can be conducted in the ambient temperature ionic liquid, l-butyl-3-methylimidazolium tetrafluoroborate (29), in which unprecedented reactivities are witnessed, and which allows easy product isolation and catalyst recycling (Eq. (60)) [96]. 

Ionic liquids have been a popular topic of interest in 2002 and a review of the applications of these solvents in organic synthesis has been published (02ACA75>. New, densely functionalized fluoroalkyl-substituted imidazolium ionic liquids have been reported <02TL9497>. An ultrasound-assisted preparation of a series of ambient-temperature ionic liquids, l-alkyl-3-methylimidazolium halides, which proceeds via efficient reactions of 1-methyl imidazole with alkyl halides/terminal dihalides under solvent-free conditions, has been described <02OL3161>. New hydrophilic poly(ethyleneglycol)-ionic liquids have been synthesized from... 

Ethylammonium nitrate (entry 18 in Table 3-1) was shown in 1914 to have m.p. 12 °C and was hence the first room temperature ionic Hquid [156] this was followed in 1967 by tetra- -hexylammonium benzoate with m.p. —50 °C (entry 26) [169], Ambient-temperature ionic liquids based on l-alkyl-3-methylimidazolium salts (entries 19-24) were first reported by Wilkes et al. in 1982 as tetrachloroaluminates [162a], Replacement of this moisture-sensitive anion by the tetrafluoroborate ion and other anions led, in 1992, to air- and water-stable, room temperature ionic liquids [162b], which have since found increasing application as reaction media for various kinds of organic reactions, mainly owing to the work of Seddon [167, 190] and Hussey [187], Suitably selected... 

Furthermore, MTO catalyzes the 1,3-transposition of allylic alcohols (eq. (2)) [12 c]. This reaction does not require the presence of peroxides or peroxo complexes. Theoretical investigations on the allylic rearrangement have also been performed [12d]. Recently it has been reported that allylic alcohols as well as alkenes can be oxidized in an ambient-temperature ionic liquid using MTO and the urea hydrogen peroxide [12 e]. 

Kosmuiski, M. and Janusz, W., Dispersions of anatase in ambient temperature ionic liquids. J. Colloid Interf. Sci., 242, 104, 2001. 

Then what are the ionic liquids In people s usual opinions, the salts that consist of organic cations and inorganic or organic anions, in the form of liquid at or around the ambient temperature, are called usually the room-temperature ionic liquid (RTIL), the ambient-temperature ionic liquid (ATIL), or the room-temperature molten salts (RTMS), the room-temperature fused salts (RTFS), and can be called the ionic liquid (IL) for abbreviation. The feature of ionic liquids being liquid at the room temperature is attributed to the asymmetric structures of the ionic liquids with big difference in volume of anions and cations leading to little electrostatic attraction. 

Lipsztajn M, Osteryoung RA (1985) Electrochemistry in neutral ambient-temperature ionic liquids 1 studies of iron(III), neodymium(III), and lithium(I). Inorg Chem 24 716-719... 

Abbott AP, Capper G, Davies DL et al (2001) Novel ambient temperature ionic liquids for zinc and zinc alloy electrodeposition. Trans Inst Met Finish 79 204-206... 

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