Efficient Synthesis of 1,3-Dialkylimidazolium-Based Ionic Liquids: The Modified Continuous Radziszewski Reaction in a Microreactor Setup

By making use of a modified Radziszewski reaction, it is demonstrated that water-soluble 1,3-dialkylimidazolium-based ionic liquids can be produced in good yields (70-90%) and purities (>95%) starting from readily available, cost-effective monoalkyl-amines, glyoxal, formaldehyde, and mineral or organic acids. The homosubstituted 1,3-dialkylimidazolium salts feature high thermal stabilities similar to those of their heterosubstituted counterparts, and relatively low viscosities, thus fulfilling the requirements for solvent application. The effect of various parameters has been studied with the goal of improving yields for both the batchwise and continuous synthesis (making use of a microreactor setup), allowing for the production of a wide variety of ionic liquids and the introduction of functionalities. The applicability of these ionic liquids is demonstrated on the example of cellulose dissolution and the dehydration of fructose to 5-hydroxymethylfurfural.