1-alkyl-3-methylimidazolium

Figure 3.1-4 Changes in liquefaction points for 1 -alkyl-3-methylimidazolium tetrafluoroborate and bis(trifyl)imide ionic liquids as a function of chain length, showing true melting points (solid fill) and glass transitions (open symbols).

Carmichael, A. J., Hardacre, C., Holbrey, J. D., Nieuwenhuyzen, M., and Seddon, K. R., Molecular layering and local order in thin films of 1-alkyl-3-methylimidazolium ionic liquids using x-ray reflectivity, Molec. Phys., 99, 795-800, 2001. 

A mixed reaction medium, composed of scC02 and ILs, has been defined as a new biphasic system by Advanced Industrial Science and Technology (AIST), and used for selective and efficient CC synthesis. For example, 1-alkyl-3-methylimidazolium salts represent a suitable system when used under supercritical conditions for the synthesis of CCs [156] from epoxides and C02. Kanawami et al. [159] have reported that the use of 1-octyl-3-methylimidazolium tetrafluoroborate under supercritical conditions resulted in a 100% conversion into PC, with 100% selectivity, within only a few minutes (Equation 7.15). 

Effect of Side Chain Length. The side chain bound to the cation also affects the Tm due to flexibility and excluded volume effects. To discuss the relation between side chain structure and Tm, the onium cation structure was fixed. The relation between the side chain structure and the thermal properties of imidazolium salts has already been reported by Seddon et al. [16, 17]. The effect of alkyl chain length of 1-alkyl-3-methylimidazolium tetrafluoroborate on the phase transition temperatures is... 

Fig. 3.1 Phase diagram for 1 -alkyl-3-methylimidazolium tetrafluorob-orate showing the melting ( ), glass (o) and clearing ( ) transitions measured by differential scanning calorimetry. Data from Ref. [16].

Both the melting point and viscosity of an ionic liquid are highly dependent on their purity and values in the literature differ accordingly. In the 1-alkyl-3-methylimidazolium tetrafluoroborate and hexafluorophosphate ionic liquids, which are the ones most widely used in catalysis thus far, halide impurities are usually present to varying degrees, due to the metathesis route commonly used for their preparation (see Section 2.3). The effect of different chloride concentrations present on the viscosity of [C4Ciim][BF4] is shown in Figure 2.5.1161... 

A number of models which can estimate density at atmospheric pressure have recently been reported. For example, Rebelo et al. [63, 64] defined the effective molar volumes of ions at 298.15 K and used the assumption of ideal behavior for the determination of the molar volume of ionic liquids. Yang et al. [65] used a theory based on the interstice model which correlated the density and the surface tension of the ionic liquid. Group contribution models have been reported by Kim et al. [66, 67] for the calculation of the density and C02 gas solubility for 1-alkyl-3-methylimidazolium based ionic liquids as a function of the temperature and C02 gas pressure with reasonable accuracy over a 50 K temperature range however, the... 

JD Holbrey, KR Seddon. The phase behaviour of 1 -alkyl-3-methylimidazolium tetrafluoroborates ionic liquids and ionic liquid crystals, J Chem Soc, Dalton Trans 2133-2139, 1999. 

All 1,3-dialkylimidazolium ILs reported to date are hygroscopic, and their miscibility with water is largely controlled by the nature of the anion. While those salts containing the nitrate, chloride and perchlorate anions are usually miscible with water in all proportions, those associated with hexafluorophosphate and bis(tri-fluoromethane) sulfonylamidate anions are almost completely immiscible with water [93]. Interestingly, the miscibility with water of those containing the tetraf lu-oroborate anion is temperature dependent (Fig. 3.5-7) [36]. It is also known that an increase of the N-alkyl chain lengths increases the hydrophobicity for a series of 1-alkyl-3-methylimidazolium hexafluorophosphate ILs [94] The miscibility of water with ILs can be increased by the addition of short-chain alcohols [95] or diminished by the addihon of salts (salting-out effect) [96]. 

Similar results were obtained for all studies (Table 2.6). All 1-alkyl-3-methylimidazolium salts tested had a polarity close to that of methanol and ethanol. The acidity of the C2-H proton was confirmed, as its substitution by a methyl group led to a less polar ionic liquid ([bmmim][NTf2], 37). No strong influence of the associated anion was observed. Imidazolium ionic liquids belong to the class of polar solvents but, although they are salts, they are still much less polar than water. On the other hand, the polarity of pyrrolidinium ionic liquids varies strongly with the anion, as shown for 1-methyl-l-(2-methoxyethyl)pyrrolidinium... 

Table 1 Selected physical chemical data of some 1 -alkyl-3-methylimidazolium-based ionic liquids...

In studies to determine the miscibility of ionic liquids with aromatic solvents, Holbrey et al. found that ionic liquid-aromatic mixtures form liquid clathrate systems. For example, ionic liquids of current interest, such as hydrophobic 1-alkyl-3-methylimidazolium salts ([Cn-mim]X) with hexafluorophosphate, / w(trifyl)imide, and tetrafluoroborate anions were observed to form liquid clathrates with benzene, toluene, and xylenes (Fig. 2). In... 

Cieniecka et al. [120] synthesized bis(trifluorDmethylsulfortyl)imide nitrate, dialkylphosphinate, trifluoromethanesulfonate, tetrafluoroborate, and hexafluoro-phosphate phosphonimn ILs and tested for antimicrobial activity and anti-electrostatic properties. They reported that phosphonium salts, in contrast to their 1-alkyl-3-methylimidazolium analogues, both cation structure and the type of anion, have effects on their biological activity. 

Use of IL in other reaction 1-Alkyl-3-methylimidazolium cation-based ILs were used for A-teri-butyloxycarbonylation of amines with excellent chemose-lectivity [32]. 1,3-dialkylimidazolitrm ILs such as [bmim][PFg]. [bmTr][PFg] and [bmTr][NTf2] were reported for reaction media for the Baylis-Hillman reaction [33]. 1-butyl-3-methylimidazohrrm-based IL [bmim][NTf2] is used as solvent for a-methylenations of carbonyl compotmds [34]. M. L. Kantam et al. described copper-catalyzed cross-coupling reaction of arylboronic acids with sulfonic acid for alkylaryl and diaryl sulfones using IL [35]. 

Ghatee MH, Moosavi P Physisorption of hydrophobic and hydrophihc 1-alkyl-3-methylimidazolium ionic liquids on the graphenes, J Phys Chem C 115(13) 5626-5636, 2011. 

Harris, K. R., Kanakubo, M., Tsuchihashi, N., Ibuki, K. and Ueno, M., Effect of pressure on the transport properties of ionic liquids 1-alkyl-3-methylimidazolium salts, J. Phys. Chem. B... 

The indices of N and C indicate the length of an alkyl chain residue (1 = methyl, 2 = ethyl and so on). COC indicates an ether residue where a number indicates the length of the aliphatic chain (C = CH2 or CH3 if terminal, C2 = C2H4 or C2H5 if terminal, and so on) [Cf mim] = 1-alkyl-3-methylimidazolium. 

We have measured liquid density and ST data in temperature ranges up to 473 and 532 K, respectively, for 1 -alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide ILs, [C Cjim][NtfJ with n = 2-10,12, and 14 (Tariq et al. [28]).Ihe aim was to test the validity of the aforementioned theories as well as the soundness of the approximations previously performed (Rebelo et al. [29]) by confronting the current results with recently obtained vapor pressure and enthalpy of vaporization data (Esperanqa et al. [30]). 

Wakai and coworkers ( Wakai et al., 2005) determined the static dielectric constants of 1-alkyl-3-methylimidazolium ionic liquids by microwave dielectric spectroscopy in the megahertz/gigahertz regime. The obtained results classify the ILs as moderately polar solvents. The observed e-values at 298.15 K fall between 15.2 and 8.8 and decrease with increasing chain length of the alkyl residue of the cation. The anion sequence is trifluoromethylsulfonate > tetrafluoroborate tetrafluorophosphate. The results indicate markedly lower polarities than the ones found by spectroscopy with polarity-sensitive solvatochromic dyes ( Wakai et al., 2005). 

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