L-alkyl-3-methylimidazolium halides

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. 

Keywords 1-metliylimidazole, alkyl halide, microwave irradiation, ionic liquids, l-alkyl-3-methylimidazolium halides... 

Ionic liquids have been a popular topic of interest in 2002 and a review of the applications of these solvents in organic synthesis has been published (02ACA75>. New, densely functionalized fluoroalkyl-substituted imidazolium ionic liquids have been reported <02TL9497>. An ultrasound-assisted preparation of a series of ambient-temperature ionic liquids, l-alkyl-3-methylimidazolium halides, which proceeds via efficient reactions of 1-methyl imidazole with alkyl halides/terminal dihalides under solvent-free conditions, has been described <02OL3161>. New hydrophilic poly(ethyleneglycol)-ionic liquids have been synthesized from... 

Alkylation of isobutane with 2-butene using various l-alkyl-3-methylimidazolium halide-aluminum chloride catalysts has been successfully demonstrated [53]. Among theses ionic liquids, [OMIM]Br-AlCl3 displayed the best performance in terms of activity and selectivity for this reaction. From various parametric studies, such as anion compositions and temperature, optimum catalytic activity was observed at 80 °C and X = 0.52. This reaction has also been used to study the Lewis acidity of ionic liquids [54]. An interesting alkylation of an aUcene can also be found in the cyclization of dodecene in a [BMIM]Q-AlCl3 (X = 0.67)/ethanol mixture at 6 MPa pressure (Scheme 5.2-14). The authors claim 27% yield and 93% selectivity for the formation of cyclododecane [55]. 

A microwave-assisted preparation of a series of l-alkyl-3-methylimidazolium halide ILs has been described [17]. The reaction is run in solvent-free conditions with a near-stoichiometric amount of reactants, and the imidazolium halides are obtained in high yield. It is also possible to perform the subsequent metathesis reaction with sodium hexafluorophosphate by means of microwave radiation and then to form the final product in a one-pot reaction [18]. Due to the fact that ILs absorb microwave energy in a very efficient way, they are believed to be well suited for large-scale microwave-assisted synthesis (that is, for reaction mixtures of more than 100 L). 

Goodchild, L, Collier, L.L., Millar, S.J., Prokes, L, Lord, J.C.D., Butts, C.P., Bowers, J. Webster, J.R.P. (2007). Structural Studies of the Phase, Aggregation and Surface Behaviour of l-Alkyl-3-Methylimidazolium Halide plus Water Mixtures, J. Colloid... 

Goodchild I, Collier L, Millar SL, Prokes I, Lord JCD, Butts CP, Bowers J, Webster JRP, Heenan RK (2007) Structural studies of the phase, aggregation and surface behaviour of l-alkyl-3-methylimidazolium halide-t water mixtures. J Colloid Interface Sci 307 455-468... 

Formation of l-alkyl-3-methylimidazolium ionic salts is usually performed by condensing 1-methylimidazole, a commercially available and inexpensive substrate, and an alkyl halide. The first synthesis of [emim] [Cl] 7 by Wilkes was carried out by heating 1-methylimidazole and an excess of chloroethane for 2 days, in the absence of solvent (Scheme 1). This procedure was improved by using an equimolar amount of the chloride reactant. ... 

Heisler, I. A. Meech, S. R. (2010). Low-frequency modes of aqueous alkali halides solutions glimpsing the hydrogen bonding vibration. Science, 327, 857-860 Holbrey, J. D. Seddon, K R. (1999). The phase behaviour of l-alkyl-3-methylimidazolium tetrafluoroborates ionic liquids and ionic liquid crystals. Journal of Chemical Society, Dalton Transaction, 2133-2139... 

Alkylation at nitrogen has been achieved by treating indole or pyrrole with alkyl halides in ionic solutions of potassium carbonate in l- -butyl-3-methylimidazolium tetrafluoroborate [bmim][BFJ <06TL2435>. Bis-protection of 3,3 -diiodo-2,2 -biindoles with Me, Boc, C02Et, or S02Ph has been described by Roy and Gribble <06SC3487>. 

The reactivity of haloalkanes in alkylation reactions also decreases with increasing chain length. In general, syntheses of salts with short alkyl substituents are more complex due to the low boiling points of the haloalkanes. The most frequently used halide salt in this field, l-ethyl-3-methylimidazolium chloride ([EMIM] Cl), is typically synthesized in an autoclave with the chloroethane cooled to below its boiling point (12 °C) before addition. 

The most common ionic liquids include alkylammonium, alkylphosphonium, A/-alkylpyridinium, and A/A/ -dialkylimidazolium cations. Two general methods for their preparation are acid-base neutralization reactions and metathesis of halide salts with a metal or ammonium salts. Alkylammonium, pyridinium, and imidazo-lium halides can be prepared by the reaction of the appropriate alkyl halide and amine. Preparation of l-ethyl-3-methylimidazolium chloride [emimjCl requires a sealed tube since it has a low boiling point. On the other hand, synthesis of [bmim] Cl can be achieved under conventional reflux conditions [33, 34]. 

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... 

The Michael-Arbuzov rearrangement is a basic reaction for the preparation of 4-coordinate species including phosphine oxides from 3-coordinate phosphorus esters, such as phosphinous esters. In most cases, the reaction requires a prolonged heating above 100 °C. Odinets et al. have now succeeded in carr5nng out the Arbuzov-reaction of ethyl diphenylphosphinite with a variety of alkyl halides in ionic liquids at or below 110 °C in short reaction times, mostly within half an hour. The best ionic liquid was l-hexyl-3-methylimidazolium bromide (Scheme 2). The recovered [hmim]Br could be recycled at least five times without a decrease in activity. 

As an example of their use in organic chemistry, the analgesic drug pravadoline has been synthesized in two steps using l-butyl-3-methylimidazolium hexafluorophosphate, abbreviated [bmim][PFe], as the solvent for both steps. The first step is a base-induced 3 2 reaction of 2-methylindole with a primary alkyl halide, and the second is a Friedel-Crafts acylation. Both steps take place in 95% yield, and the ionic solvent is recovered simply by washing the reaction mixture, first with toluene and then with water. We ll be hearing a lot more about ionic solvents in coming years. 

A heterogeneous catalytic method based on copper(I) chloride absorbed on Kieselghur provides an efficient and convenient oxidation of alkyl halides and alkyl tosylates to the corresponding aldehydes. Ionic liquids, such as l-butyl-3-methylimidazolium... 

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