L-Butyl-3-methylimidazolium cation

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... 

Ozawa, R., Hayashi, S., Saha, S., Kobayashi, A., and Hamaguchi, H., Rotational isomerism and structure of the l-butyl-3-methylimidazolium cation in the ionic liquid state, Chem. Lett., 32, 948-949, 2003. 

The use of two-phase catalysis in water or high-polar organic solvents is one of best approaches to clean catalytic hydrogenation (Hermann and Kohlpainter, 1993). Ionic solvents with a wide range of liquid phase (down to -81°C) based on l- -butyl-3-methylimidazolium cations can be used in these reactions. 

In the case of the l-butyl-3-methylimidazolium cation a stable radical is obtained... 

The ionic liquid based on the l- -butyl-3-methylimidazolium cation was also used as an efficient catalytic medium for the chemoselective dithioacetalization of carbonyl compounds. This reaction proceeded with both activated and weakly activated aromatic aldehydes in almost quantitative yields in short reaction times. In addition, an acid-sensitive substrate such as furfural also gave the corresponding 1,3-dithiolane without a formation of any side products (Table 8). Moreover, aromatic ketones did not produce dithioketals under the same reaction conditions (room temperature, 10-20 min) or even after a prolonged reaction time <2004ASC579>. 

Broeke J V D, Stam M, Lutz M, et al. Designing ionic hquids l-butyl-3-methylimidazolium cations with substimted tetraphenylbo-rate counterions. Eur. J. Inorg. Chem. 2003. 2003, 2798-2811. 

Figure 6 Viscosity of [bmim][BF4] versus molal concentration of chloride added as [bmim]Cl at 20 °C (where [bmim] is the l-butyl-3-methylimidazolium cation).

To prove our hypothesis on the organocatalytic effects of anions, we chose a series of relatively basic anions, combined with l-butyl-3-methylimidazolium cations. Surprising results were obtained in the esterification of benzyl alcohol and acetic acid, which not only showed that the yields with any of the ionic liquids investigated are much lower than in the absence of ionic liquid (27% after 5 h 75-80% after 100 h in equilibrium), but also that in none of the cases equilibrium was reached after 5 h at 100 °C (ROH R COOH ionic liquid = 1 1.5 1). However, slight effects of the nature of the anion were observed, giving decreasing reaction... 

This result is in sharp contrast with earlier assumptions that due to the inherently weak interactions between the chloride anion and the l-butyl-3-methylimidazolium cation (ca. ISkJmoP ), chloride dissociation from a transition metal complex can be thermodynamically disfavored in ILs. ... 

The reason for the fact that ILs melt at low temperatures is not completely understood, but the asymmetry of the cation seems to play an important role (Seddon, 1996a,b) asymmetry causes packing inefficiency and hence prevents crystallization. Thus, for example, salts of the asymmetrical l-butyl-3-methylimidazolium cation with only Q symmetry exhibit lower melting points than analogous salts with cations of higher symmetry, such as 1-butylpyridinium with symmetry (Holbrey et al., 2003). The same is true for symmetrically 1,3-dialkylsubstituted imidazolium, and imidazolium with two different A/,Af -alkyl residues (Plechkova and Seddon, 2008 Seddon, 1997). 

Suarez et al. (1998) gave an account of the physical properties of air- and water-stable ILs bearing l-butyl-3-methylimidazolium cation, [BMIM]+, with tetrafluoroborate BF4 and hexafluorophos-phate PFg, respectively, as anions. These viscous liquids show a wide liquidus range (down to -81°C) and a wide electrochanical window (up to 7.0 V). Infrared spectroscopy shows a characteristic... 

Jin H, O Hare B, Dong J, Arzhantsev S, Baker GA, Wishart JF, Benesi AJ, Maroncelli M (2008) Physical properties of ionic liquids consisting of the l-butyl-3-methylimidazolium cation with various anions and the bis(trifluoromethylsulfonyl)imide anion with various cations. J Phys Chem B 112(l) 81-92... 

Katoh Takahashi studied photochemical degradation under pulsed laser irradiation in order to examine the decomposition behaviour of l-methyl-3-butylimidazolium bis[(trifluoromethyl)sulphonyl]amide and iodide. They concluded that the excited state l-butyl-3-methylimidazolium cation ([BMIM ] ) underwent degradation efficiently and suggested that the neutral l-butyl-3-methylimidazolium radical ([BMIM] ) was relatively stable (Katoh Takahashi, 2009). The majority of studies have looked at the photodegradation of imidazolium-based ILs. Nevertheless, there is some information on the photochemical transformations of pyridinium salts, which could be a good starting point for later IL degradation studies (Damiano et al., 2007). 

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