L-butyl-3 methylimidazolium hexafluorophosphate

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

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 reaction conditions were room temperature and pressure and the IL was developed from l-butyl-3-methylimidazolium hexafluorophosphate using 1-4 mol% Pd(OAc)2, 1 mol % Lewis acid, and 0.5 mL of IL. The reaction times were from 2.5 to 4.5 h. The Lewis acids were chosen from the following Cu(OTf)2, Cu(CF3C02)2, Zn(OTf)2, and In(OTf)3. 

Three ionic liquids were purchased from Aldrich l-butyl-3-methylimidazolium chloride, l-butyl-3-methylimidazolium hexafluorophosphate and l-butyl-3-methylimidazolium tetrafluoroborate. Homogeneous Co (II) catalyst precursors used in our experiments include Co(BF4)2, Co(OAc)2, and Co(C104)2 each of which have high solubilities in above ionic liquids. High surface area catalyst supports Si02 and AI2O3 were obtained from Davison and Engelhard, respectively. 

Zafarani-Moattar, M.T. and Shekaari, H. Volumetric and speed of sound of ionic liquid, l-butyl-3-methylimidazolium hexafluorophosphate with acetonitrile and methanol at T = (298.15 to 318.15) K, /. Chem., Eng. Data, 50,1694,2005. Wang, J. et al.. Excess molar volumes and excess logarithm viscosities for binary mixtures of the ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate with some organic solvents, /. Solution Chem., 34, 585, 2005. 

Swatloski, R.P., Holbrey, J.D., and Rogers, R.D., Ionic liquids are not always green hydrolysis of l-butyl-3-methylimidazolium hexafluorophosphate. Green Chem., 5, 361-363, 2003. 

Carda-Broch, S., Berthod, A., and Armstrong, D. W., Solvent properties of the l-butyl-3-methylimidazolium hexafluorophosphate ionic liquid. Anal. Bioanal. Chem., 375,191-199, 2003. 

Jacquemin, J. et al.. Low-pressure solubilities and thermodynamics of solvation of eight gases in l-butyl-3-methylimidazolium hexafluorophosphate. Fluid Phase Equilib., 240, 87, 2006. 

Wang, J.-H., Cheng, D.-H., Chen, X.-W., Du, Z., Fang, Z.-L., Direct extraction of double-stranded DNA into ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate and its quantification. Anal. Chem., 79, 620-625, 2007. 

Antony, J. H., Mertens, D., Dolle, A. et al.. Molecular reorientational dynamics of the neat ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate by measurement of nuclear magnetic relaxation data., ChemPhysChem., 4, 588, 2003. 

Umecky, T, Kanakubo, M., and Ikushima, Y., Self-diffusion coefficients of l-butyl-3-methylimidazolium hexafluorophosphate with pulsed-field gradient spin-echo NMR technique. Fluid Phase Equilib., 228-229, 329, 2005. 

This structural change is suppressed by the addition of tetrahydrothiophene (THT)19b. It prevents the formation of polymethylene zinc, i.e. (—CH2Zn—) . Without THT, a solution of 3 in THF yields polymethylene zinc at 60 °C. Monomeric bis(iodozincio)methane (3) is much more active for methylenation as compared to polymethylene zinc. As shown in Table 3 (entry 3), the addition of THT to the reaction mixture at 60 °C improved the yield of the alkene dramatically. Practically, however, its stinking property makes the experimental procedure in large scale uncomfortable. Fortunately, an ionic Uquid, l-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), plays the same role. Ionic liquid also stabilizes the monomeric structure of 3 even at 60 °C and maintains it during the reaction at the same temperature. The method can be applied to various ketones as shown in Scheme 14.4... 

The use of ionic liquids in microwave chemistry has great potential and a number of research groups have introduced the use of ionic liquids in synthetic approaches43,44. l-Butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) was recently evaluated as a solvent for the microwave-promoted Heck reaction45. Terminal arylations of electron-poor olefins were carried out rapidly with good-to-excellent yields, using the old-fashioned catalyst palladium chloride (Scheme 2.15). As an example, the... 

The Kotsuki group investigated the effect of high-pressure conditions on the direct proline-catalyzed aldol reaction [79a], a process which, interestingly, does not require use of DMSO as co-solvent. Use of high-pressure conditions led to suppression of the formation of undesired dehydrated by-product and enhancement of the yield. Study of the substrate range with a range of aldehydes and ketones revealed that enantioselectivity was usually comparable with that obtained from experiments at atmospheric pressure. Additionally, proline catalyzed aldol reactions in ionic liquids, preferably l-butyl-3-methylimidazolium hexafluorophosphate, have been successfully carried out [79b,c]. 

Swatloski, R. P., Holbrey, J. D., Rogers, R. D. (2003), Ionic Liquids are not always Green Hydrolysis of l-butyl-3-Methylimidazolium Hexafluorophosphate, Green Chem. 5, 361-363. 

Anthony, J. L., Maginn, E. J., Brennecke, J. F. (2002), Solubilities and Thermodynamic Properties of Gases in the Ionic Liquid l- -Butyl-3-methylimidazolium Hexafluorophosphate, J. Phys. Chem. B 106, 7315-7320. 

Yet the relationship between solute chemical structure and diffusion is not always simple. Werner et al. [248] conducted fluorescence correlation spectroscopic studies of three fluorescent probes in l-butyl-3-methylimidazolium hexafluorophosphate. The probes were chosen to be of comparable molecular structure, but possessed positive, negative, and neutral charges. The authors found that while the neutral probe diffused more rapidly than the cationic probe, the anionic probe diffused the most quickly. 

Recently, Yao showed that osmium tetroxide could be immobilized in an ionic liquid. The recyclability of osmium tetroxide was improved by the addition of DMAP. Both the catalyst and the ionic liquid were reused in six consecutive runs without significant reduction in yield [47]. Dihydroxylations in a solvent mixture of l-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF6), tert-butanol, and water with 0s04 (2 mol%), DMAP (2.4 mol%), and NMO (1.1 equivalents) as cooxidant afforded diols in good yield (73-99% depending... 

Suarez et al. [457] prepared and investigated the electrochemical window for the following ionic liquids l-n-butyl-3-methylimidazolium tetrafluoro-borate (BMI+)(BF4 ) and l-butyl-3-methylimidazolium hexafluorophosphate (BMF)(PF ) on tungsten and vitreous carbon. They found the following values for the electrochemical window 6.1 V and 5.45 V for (BMI+)(BF4 ) and 7.1 V and 6.35 V for (BMI+)(PF6 ), respectively. 

The use of Cu in combination with TEMPO also affords an attractive catalyst [200, 201]. The original system however operates in DMF as solvent and is only active for activated alcohols. Knochel et al. [202] showed that CuBr.Me2S with perfluoroalkyl substituted bipyridine as the ligand and TEMPO as cocatalyst was capable of oxidizing a large variety of primary and secondary alcohols in a fluorous biphasic system of chlorobenzene and perfluorooctane (see Fig. 4.69). In the second example Ansari and Gree [203] showed that the combination of CuCl and TEMPO can be used as a catalyst in l-butyl-3-methylimidazolium hexafluorophosphate, an ionic liquid, as the solvent. However in this case turnover frequencies were still rather low even for benzylic alcohol (around 1.3 h 1). 

Berthod, A. and Carda-Broch, S. 2004. Use of the ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate in countercurrent chromatography. Analytical and Bioanalytical Chemistry, 380 168-77. 

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