L-butyl-3 methylimidazolium

Figure 4.2-1 shows the calculated ab initio molecular structure of the ionic liquid [BMIM][PFg] (l-butyl-3-methylimidazolium hexafluorophosphate). 

A new class of solvents called ionic liquids has been developed to meet this need. A typical ionic liquid has a relatively small anion, such as BF4, and a relatively large, organic cation, such as l-butyl-3-methylimidazolium (16). Because the cation has a large nonpolar region and is often asymmetrical, the compound does not crystallize easily and so is liquid at room temperature. However, the attractions between the ions reduces the vapor pressure to about the same as that of an ionic solid, thereby reducing air pollution. Because different cations and anions can be used, solvents can be designed for specific uses. For example, one formulation can dissolve the rubber in old tires so that it can be recycled. Other solvents can be used to extract radioactive waste from groundwater. 

Based on the properties of ionic hquids in high-temperature microwave-enhanced reactions, the authors chose l-butyl-3-methylimidazolium tetraflu-orophosphate ([bmimjPFe) as the suitable ionic liquid (Scheme 23). The addition of 0.15 mmol of [bmimjPFe to a reaction in 2.0 mL of DCF was found to increase the reaction rate dramatically and a set-temperature of 190 °C was reached in a mere 1 min, while the reactions programmed at 190 °C, in the absence of the ionic liquid, reached only 170 °C in 10 min. The reactions were finished in a mere 18-25 min of irradiation time, including the hydrolysis of the sensitive imidoyl chloride moiety with water. The formed bis-lactams were isolated in good yield and purity. 

Lipases from C. antarctica and P. cepacia showed higher enantioselectivity in the two ionic liquids l-ethyl-3-methylimidazolium tetrafluoroborate and l-butyl-3-methylimidazolium hexafluoroborate than in THE and toluene, in the kinetic resolution of several secondary alcohols [49]. Similarly, with lipases from Pseudomonas species and Alcaligenes species, increased enantioselectivity was observed in the resolution of 1 -phenylethanol in several ionic liquids as compared to methyl tert-butyl ether [50]. Another study has demonstrated that lipase from Candida rugosa is at least 100% more selective in l-butyl-3-methylimidazolium hexafluoroborate and l-octyl-3-nonylimidazolium hexafluorophosphate than in n-hexane, in the resolution of racemic 2-chloro-propanoic acid [51]. 

Cull and co-authors reported a microbe-mediated transformation of benza-mide from benzonitrile in a mixed solvent of IL, l-butyl-3-methylimidazolium... 

The dehydration of fructose 40 or glucose into 5-hydroxymethylfurfural 41 is a process which has been exploited to convert biomass into higher value products. The reaction has been achieved using a chromium NHC complex, formed in situ from CrCl and the NHC 42 (Scheme 11.10) [16], The reaction is performed in the ionic liquid BMIM+Cl (l-butyl-3-methylimidazolium chloride). 

When the same [NiI (NHC)2] complexes are employed as alkene dimerisation catalysts in ionic liquid (IL) solvent [l-butyl-3-methylimidazolium chloride, AICI3, A-methylpyrrole (0.45 0.55 0.1)] rather than toluene, the catalysts were found to be highly active, with no evidence of decomposition. Furthermore, product distributions for each of the catalyst systems studied was surprisingly similar, indicating a common active species may have been formed in each case. It was proposed that reductive elimination of the NHC-Ni did indeed occur, as outlined in Scheme 13.8, however, the IL solvent oxidatively adds to the Ni(0) thus formed to yield a new Ni-NHC complex, 15, stabilised by the IL solvent, and able to effectively catalyse the dimerisation process (Scheme 13.9) [25-27],... 

Alammar and Mudring [17] have also synthesized ZnO in the form of nanorods with lengths from 50-100 nm and diameters of about 20 nm (Fig. 8.5.) using the ionic liquid l-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, [C4mim][Tf2N]. 

Even though Ti02-based materials have been far more investigated than any other photocatalyst and this chapter is dedicated to these systems, it is important at least to mention here some of the promising alternative materials studied for wastewater treatment. CdS hollow nanospheres were prepared in a single-step hydrothermal route by Li et al. [109] using the ionic liquid l-butyl-3-methylimidazolium... 

Alkylation at nitrogen has been achieved by treating indole or pyrrole with alkyl halides in ionic solutions of potassium carbonate in l- -butyl-3-methylimidazolium tetrafluoroborate [bmim][BFJ <06TL2435>. Bis-protection of 3,3 -diiodo-2,2 -biindoles with Me, Boc, C02Et, or S02Ph has been described by Roy and Gribble <06SC3487>. 

Scheme 6.93) [192]. Using either of the two solvent systems, all studied cycloaddition reactions were completed in less than 1 min upon microwave irradiation at 50 °C employing 3 mol% of the catalyst. An additional advantage of using the ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) as solvent is that it facilitates catalyst recycling. 

Inter- and intramolecular hetero-Diels-Alder cycloaddition reactions in a series of functionalized 2-(lH)-pyrazinones have been studied in detail by the groups of Van der Eycken and Kappe (Scheme 6.95) [195-197]. In the intramolecular series, cycloaddition of alkenyl-tethered 2-(lH)-pyrazinones required 1-2 days under conventional thermal conditions involving chlorobenzene as solvent under reflux conditions (132 °C). Switching to 1,2-dichloroethane doped with the ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) and sealed-vessel microwave technology, the same transformations were completed within 8-18 min at a reaction temperature of 190 °C (Scheme 6.95 a) [195]. Without isolating the primary imidoyl chloride cycloadducts, rapid hydrolysis was achieved by the addition of small amounts of water and subjecting the reaction mixture to further microwave irradia-... 

The ruthenium cluster [Ru4H4(//6-C6H6)4]2+ was also employed for the hydrogenation of arenes in a biphasic water/l-butyl-3-methylimidazolium tetrafluoro-borate biphasic system. At 90°C and 60 bar H2, benzene was reduced to cyclohexane with a TOF of 364. 

The l-butyl-3-methylimidazolium cation, bmim (Fig. 1), makes a number of ILs with varying properties, when combined with different anions [4]. BmimCl and bmimBr are crystals at room temperature, while bmimi is a RIL. By cooling down molten bmimCl and bmimBr below the melting points, their... 

Prior to the study of Jacobs, Song et al. [87] had already reported monomeric Cr-salen 63 catalyzed ARO of epoxides with TMSN3 in ionic liquid l-butyl-3-methylimidazolium salts [bmim][X]. The ARO reaction proceeded readily at room temperature with easy catalyst/solvent recycling and does not include hazardous workup stages such as distillation of the azide product. 

Ionic liquids, having per definition a melting point below 100 °C, and especially room temperature ionic liquids (RTIL) have attracted much interest in recent years as novel solvents for reactions and electrochemical processes [164], Some of these liquids are considered to be green solvents [165]. The scope of ionic liquids based on various combinations of cations and anions has dramatically increased, and continuously new salts [166-168] and solvent mixtures [169] are discovered. The most commonly used liquids are based on imidazolium cations like l-butyl-3-methylimidazolium [bmim] with an appropriate counter anion like hexafluorophos-phate [PFg]. Salts with the latter anion are moisture stable and are sometimes called third generation ionic liquids. 

Putilova ES, Troitskii NA, Zlotin SG, Khudina OG, Burgart YV, Saloutin VI, Chupakhin ON (2006) One-step solvent-free synthesis of fluoroalkyl-substituted 4-hydroxy-2-oxo(thioxo) hexahydropyrimidines in the presence of l-butyl-3-methylimidazolium tetrafluoroborate. Russ J Org Chem 42 1392-1395... 

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