L-alkyl-3-methylimidazolium

Scheme 4.18 Microwave syntheses in l-alkyl-3-methylimidazolium ionic liquids (see text for references).

The polarity of some l-alkyl-3-methylimidazolium ionic liquids has been determined using the solvatochromic dyes Nile Red and Reichardt s dye [16, 17], Measurements with Nile Red do not give absolute values of polarity but provide a useful scale to estimate the relative polarity of the ionic liquids. Similar measurements have been made using a number of other solvatochromic dyes (dansylamide, pyrene, pyrenecarboxyaldehyde, and bromonapthalene) for [BMIM][PF6], and gave results consistent with those obtained with Nile Red. Values for Ej obtained for ionic liquids generally fall between the values of 0.6 and 1.0, as shown in Table 4.3. 

Holbrey, J. D. Seddon, K. R. The phase behaviour of l-alkyl-3-methylimidazolium tetrafluoroborates ionic liquids and ionic liquid crystals, J. Chem. Soc., Dalton Trans., 1999, 2133-2139. 

Seddon, K. R. Stark, A. Torres, M.-J. Influence of chloride, water, and organic solvents on tbe physical properties of ionic liquids. Pure Appl. Chem., 2000, 72(12), 2275-2287 Seddon, K. R. Stark, A. Torres, M. J. Viscosity and density of l-alkyl-3-methylimidazolium ionic liquids, in Clean Solvents Alternative Media for Chemical Reactions and Processing, Eds. Abraham, M. Moens, L. ACS Symposium Series, Vol. 819, American Chemical Society, Washington D.C., 2002, pp. 34-49. 

Figure 11. Raman spectra of l-alkyl-3-methylimidazolium tetrafuluoroborate, C mim[BF4] ...

The general observations made regarding structural influences on melting points are transferable across cation type, and apply in each case. The primary focus is on l-alkyl-3-methylimidazolium cations, coupled with simple organic and inorganic anions. Complex anions, such as mixed /MX systems, are mentioned, as are other series of cations (including some examples of tetraalkylammonium salts). 

Figure 3.1-2 Thermal decomposition temperature ranges (in °C) for ionic liquids containing l-alkyl-3-methylimidazolium cations. The thermal stability of the ionic liquids depends on the nucleophilicity of the anion.

In general, isotopic exchange is both expensive and difficult. In tlie case of many room-temperature ionic liquids, however, the manufacture of deuterated ionic Hq-uids is relatively easily achievable. For example, the general synthesis of l-alkyl-3-methylimidazolium salts is shown in Scheme 4.1-1 [2]. This methodology allows maximum flexibility in the deuteration on the imidazolium cation that is, it can be either ring or side chain deuteration or both. 

Similar lamellar structures are formed for l-alkyl-3-methylimidazolium cations with [PdCl4] when n > 12. As with the pyridinium systems, mesomorphic liquid crystal structures based on the smectic A structure are formed [24]. 

Nishida, T., Tashiro, Y., and Yamamoto, M., Physical and electrochemical properties of l-alkyl-3-methylimidazolium tetrafluoroborate for electrolyte. Fluorine Chem., 120,135,2003. 

Lee, S.H. and Lee, S.B., The Hildebrand solubility parameters, cohesive energy densities and internal energies of l-alkyl-3-methylimidazolium-based room temperature ionic liquids, Chem. Commun., 3469, 2005. 

Domarfeka, U., Bogel-Lukasik, E., and Bogel-Lukasik, R., 1-Octanol/water partition coefficients of l-alkyl-3-methylimidazolium chloride, Chem. Eur. J., 9,3033,2003. 

Domariska, U. and Marciniak A., Solubility of l-alkyl-3-methylimidazolium hexafluorophosphate in hydrocarbons, ]. Chem. Eng. Data, 48, 451,2003. 

Domariska, U., Pobudkowska, A., and Eckert, R, (Liquid + liquid) phase equilibria of l-alkyl-3-methylimidazolium methylsulfate with alcohols, ethers, ketones, /. Chem. Thermodyn., 38,685, 2006. 

Lachwa, J. et al.. Changing from an unusual high-temperature demixing to a UCST-type in mixtures of l-alkyl-3-methylimidazolium bis (trifluoromethyl) sulfonyljamide and arenes. Green Chem., 8, 262, 2006. 

Arce, A. et al.. Separation of benzene and hexane by solvent extraction with l-alkyl-3-methylimidazolium bis (trifluoromethyl)sulfonyl amide ionic liquids effect of the alkyl-substituent length, /. Phys Chem. B, 111, 4732,2007. 

Figure 5.4 Scheme illustrating the mechanism for separation of polyphenols using l-alkyl-3-methylimidazolium-based ionic liquids. (Adapted from Yanes, E. G., Gratz, S. R., Baldwin, M. J., Robison, S. E., and Stalcup, A. M., Anal. Chem., 73,3838-3844,2001.)... 

Jiang, T.-F., Gu, Y.-L., Liang, B., Li, J.-B., Shi, Y.-R, and Ou, Q.-Y., Dynamically coating the capillary with l-alkyl-3-methylimidazolium based ionic liquids for separation of basic proteins by capillary electrophoresis. Anal. Chim. Acta, 479, 249-254, 2003. 

Yue, M.-E. and Shi, Y.-R, Application of l-alkyl-3-methylimidazolium-based ionic liquids in separation of bioactive flavonoids by capillary zone electrophoresis, /. Sep. Set., 29, 272-276,2006. 

Wasserscheid and coworkers were the first to attempt to use ILs for the desulfurization of model solutions (dibenzothiophene [DBT], in n-dodecane) and real diesel fuels [41]. For extraction, the authors used ILs with l-alkyl-3-methylimidazolium cations ([C CiIm], n = 2, 4, 6) and various anions. Also, binary mixtures of l-alkyl-3-methylimidazolium chloride with AICI3 (Lewis-acidic ILs), the equimolar mixture of cyclohexyldiethylammonium and tri-butylammonium mefhanesulfonates (Brnnsted-acidic IL) and the equimolar mixture of cyclohexyldiefhylmethylammonium and tributylmefhylammo-nium methanesulfonafes were tested. 

Huddleston, J. G., Broker, G. A., Willauer, H. D., Rogers, R. D., Free-energy relationships and solvatochromatic properties of l-alkyl-3-methylimidazolium ionic liquids. In Ionic Liquids, ACS Symposium Series 818, 270-288, 2002. 

One aspect that limits the use of ILs in optical applications is that many synthetic methodologies lead to yellowish or even brown ILs. Specifically, during fhe preparation of l-alkyl-3-methylimidazolium halides that are frequently used as starting materials in the synthesis of other ILs, discoloration is difficult to avoid. Thus, most commercially available ILs contain colored impurities. Apparently these impurities do not affect organic or catalytic reactions which are carried out in ILs. 

Figure 12.17 Raman spectra of l-alkyl-3-methylimidazolium tetrafluoroborate liquids, [C CiIm][Bp4] for n = 10, 8, 7, 6, 5, 4, 3, and 2. (Adapted from Hamaguchi, H., and Ozawa, R., Adv. Chem. Phys., 131,85-104, 2005. With permission.)...

Bradley, A. E., Hardacre, C., Holbrey, J. D., Johnston, S., McMath, S. E. J., and Nieuwenhuyzen, M., Small-angle x-ray scattering studies of liquid crystalline l-alkyl-3-methylimidazolium salts, Chem. Mater., 14,629-635,2002. 

Berg, R. W., Deetlefs, M., Seddon, K. R., Shim, 1., and Thompson, J. M., Raman and ab initio studies of simple and binary l-alkyl-3-methylimidazolium ionic liquids, ]. Phys. Chem. B, 109,19018-19025, 2005. See also supplementary information at http //pubs.acs.org/subscribe/journals/jpcbfk/suppinfo/jp050691r/ jp050691rsi20050208 105000.pdf. 

Urahata, S. M., and Ribeiro, M. C. C., Structure of ionic liquids of l-alkyl-3-methylimidazolium cations A systematic computer simulation study, /. Ghent. Phys., 120, 1855-1863, 2004. 

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