L-n-alkyl-3-methylimidazolium

Diedenhofen M, Klamt A, Marsh K et al. (2007) Prediction of the vapor pressure and vaporization enthalpy of l-n-alkyl-3-methylimidazolium-bis-(trifluoromethanesulfonyl) amide ionic liquids. Phys Chem Chem Phys 9 4653 1656... 

Zhang D, Okajima T, Matsumoto F, Ohsaka T (2004) Electroreductirai of dioxygen in l-n-alkyl-3-methylimidazolium tetrafluoroborate room-temperature ionic liquids. J Electrochem Soc 151(4) D31-D37... 

A major characteristic of ionic liquids, however, is fliat diey have a nearly negligible vapor pressure which makes accurate measurements problematic. Although the possible number of ionic liquids formulations is large, there are only a limited number of studies that provide vapor-pressure data, and most of them were conducted at temperatures far in excess of relevant environmental conditions. For example, Zaitsau et al measured the vapor pressure of l-n-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide in the temperature range of 165 to 244°C. 

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

Figure 4.2-6 shows RDFs for the center of mass of [PFe] with the l-n-butyl-3-methylimidazolium [BMIM]" and [BMMIM]+ cations. The first sharp peak in g(r) for the [BMIM][Pp6] system is due to the anion localizing near the C2 carbon of the ring (the carbon between the two nitrogens). This behavior has been observed in nearly all simulations involving l-alkyl-3-meth)dimidazolium cations [11,12,14,15,... 

Butanol,. sec-butanol, rerr-butanol, and n-octanol were converted to their corresponding alkyl halides at room temperature using l-n-butyl-3-methylimidazolium halides in the presence of a Brpnsted acid (typically H2S04). Reaction conditions are significantly milder than those required by classical methods, and the products are easily removed from the reaction mixture. The proposed mechanism involves protonation of the alcohol followed by... 

Carter [9] and AlNashef [10] research works were focused on imidazohum-based ILs with similar structures (e.g. l-n-aIkyl-3-methylimidazolium), differing only in the length of the alkyl chain at the 1-position and the nature of the anion (Cl vs. PFg ), however, only the latest study showed reversibility of the 02/02 redox couple. Therefore, these contradictory results indicated that a deeper knowledge of the influences of the cations and anions of the imidazolium-based ILs on the oxygen reduction reaction was stiU needed. 

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]. 

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. 

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.)...

More than 600 ionic liquid systems can, in principle, be generated from around 10 simple anions such as (BF4)" and (PFg) and the l-alkyl-3-methylimidazolium cation substimted with various alkyl groups in the 2-, 4-, or 5-position, or N-alkylpridinium substimted in the 3- or 4-position. When heteropolyanions and tetrafkylammonium and tetraalkylphosphonium cations are added to the hst, a grand total of more than a quarter of a million ionic liquid systems is possible. 

Separation of C02 from N2 or CH4 comprises an area of critical industrial, social, and environmental importance where room-temperature ionic liquids (RTILs) are showing great potential [3, 63, 64], The commonly used ILs for this purpose are l-alkyl-3-methylimidazolium salts, represented by the formula [C MIm][X, where C is an n-alkyl chain of varying length and X is typically a molecular anion with a delocalized negative charge, such as bis(trifluorome-thane)sulfonimide, [Tf2N ] (Scheme 4.4) [65-71]. 

Note on nomenclature, l-alkyl-3-methylimidazolium cations will be abbreviated throughout this Chapter as [C tnim]+, where n is the lenght of the alkyl chain. 

Fig. 3.2 Relation between thermal decomposition temperature (Td) of l-alkyl-3-methylimidazolium-type ILs with alkyl chain length (n). Anion species are CC ( ), I- ( ), BF4(A), PF - ( ) and TFSI ( ).

In another approach, the dehydration has been conducted in ionic liquids (l-alkyl-3-methylimidazolium chloride) under acid or metal chloride catalysis yielding HMF up to more than 80% nearly without any formation of by-products like levulinic acid [32], When using chromium(II) chloride as catalyst even D-glucose could be used as feedstock since this catalyst is effective for the in situ isomerization of o-glucose to o-fructose before dehydration takes place to produce HMF in 70% yield. The catalyst system N-heterocyclic carbene/CrCU in l-butyl-3-methyl imidazolium chloride has been developed for the selective conversion of D-fructose (96% yield) and o-glucose (81% yield) [33]. 

The preparation of these salts is usually performed by a simple N-alkylation of 1-methylimidazole generating a l-alkyl-3-methylimidazolium cation followed by anion metathesis [27]. The synthesis can also start with imidazole, which is consecutively alkylated with alkyl hahdes (Scheme 3.5-9). The 1,3-dialkylimidazolium cations will be abbreviated throughout this section as [C Cylm], where Im stands for imidazolium and x and y are the number of the carbons of the alkyl chains. 

In contrast to sodium, a residual Lewis base such as the starting N-alkylimidazole can severely poison organometallic catalysts. These compounds are coordinating bases and have been proven difficult to remove from ILs due to their high boiling points. A simple colorimetric method of detection was first developed, which is based on the complexation of N-methylimidazole with copper(II) chloride [13]. ft enables monitoring of N-methyhmidazole content in [EM1][C1] to better than 0.2 mol%. More recently, capillary electrophoresis was applied for the detection of imidazole derivatives in l-alkyl-3-methylimidazolium salts [14]. Using this technique, it is then possible to separate and identify the different N-alkylimidazole and imidazolium cations in the ILs. 

Giridhar, P., Venkatesan, K., Srinivasan, T., Rao, P. V. (2004). Effect of alkyl group in l-alkyl-3-methylimidazolium hexafluorophosphate ionic liquids on the extraction of uranium by tri-n-butylphosphate diluted with ionic liquids. Journal of Nuclear Radiochemical Science, 5, 21-26. 

M.N. Garaga, M. Nayeri, A. MartineUi, Effect of the alkyl chain length in l-alkyl-3-methylimidazolium ionic liquids on inter-molecular interactions and rotational dynamics, J. Mol. Liq. 210 (Pt. B) (2015) 169-177. 

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