MRT - Ionic Liquids

By: Matthias Junkers, Aldrich ChemFiles 2009, 9.4, 11.

Aldrich ChemFiles 2009, 9.4, 11.

Benefit from MRT & Flow Chemistry: Green production of a highly pure product with 100% yield thanks to precise control over reaction temperature.

The production of certain ionic liquids in high purity is a special challenge. The reaction between imidazole derivatives with sulfonates is extremely exothermic (Scheme 3). Conventional batch synthesis procedures fail to give purities higher than 96%. Even with very slow dosing times and careful cooling, batch reactors are heated up by the reaction. Our investigations show that brown impurities are formed if the temperature rises over 20 °C in any part of the batch reactor leading to an ugly colored product. Subsequent purification is troublesome and can only be achieved with huge efforts. Microreactors solve this dilemma with their superior heat exchange capabilities allowing synthesis with neat reagents with external cooling of -3 °C. Under these conditions the temperature inside the microreactor in the reaction zone is kept at a constant value of 8 °C. These are the perfect conditions to produce EMIm triflate (00738) with a purity exceeding 99%, and only traces of undesired materials (methylimidazole <50 mg/kg, water < 0.02%). Since neat reagents can be used without any solvent, the output of this procedure is very high. 1.5 kg of EMIm triflate (00738) is produced in just one hour. The synthesis procedure has been easily adapted to other substrates that can be found in the Sigma-Aldrich catalogs.

Scheme 3: Ionic liquids production (00738)

There is a lot of discussion questioning whether ionic liquids can generally be called ‘green’. While this may be debatable production of ionic liquids in a microreactor is potentially as ‘green’ as chemical synthesis can be; as reagents are quantitatively converted into the final product, no solvents are needed for synthesis or purification and absolutely no waste is generated.

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