Preparation of imidazolium halides

Efforts have been made to accelerate the reaction. Ionic liquids can be obtained in 1 min using microwave-assisted preparation, and ultrasound-assisted synthesis leads to the rapid isolation of ionic liquids with high chemical purity. If a microwave reactor with reaction condition control mechanisms is used, ionic liquids can be conveniently prepared even on a large scale (up to 2 moles), both in high yields and with short reaction times.  

It is also known that condensation can be accelerated by using bromide or iodide derivatives instead of chloride ones. Other procedures involving the use of solvents (tetrahydrofuran (THE), chloroform, 1,1,1 -trichloroethane) have been proposed, but since one of the objectives of ionic liquids is to lead to environmentally clean processes, their preparation should, as far as possible, be performed under neat conditions (absence of solvent). 

Simpler procedures can be used for the preparation of symmetrical 1,3-dialkyl-imidazolium salts. Heating an excess of chloride derivative with A -trimethylsilylimidazole 10 in toluene at 110 C produces the desired salts in 

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Ionic liquids used as solvents have to be isolated with high chemical purity. Their non-volatility is a disadvantage in terms of their preparation because, unlike classical solvents, they cannot be purified by distillation. The starting materials are therefore purified. Typically, for fhe preparation of imidazolium halides, 1 -methylimidazolium must be distilled over NaOH and the haloalkane should be washed with concentrated sulfuric acid (to remove coloration), neutralized with an NaHCOs solution, washed with water, dried and distilled before use. 

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