Solid-to-Liquid Mechanochemistry: Multiscale Synthesis of Electrochemically Relevant Ionic Liquids

Abstract

Ionic liquids (ILs) offer unique properties for electrochemical applications, but their synthesis typically requires large volumes of solvents and costly reagents, limiting scalability and sustainability. Here, we address this limitation by demonstrating a solventfree mechanochemical route to five benchmark ILs of electrochemical relevance. The method enables the synthesis of both hydrophobic Pyr₁₄TFSI (1-butyl-1methylpyrrolidinium bis(trifluoromethanesulfonyl)imide) and hydrophilic Pyr₁₄TfO (1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate) ILs via solid-state metathesis reaction induced by mechanical mixing, requiring only minimal solvent for product recovery. This approach delivers high yields (> 80%) and nearly quantitative conversions (≥ 99%), producing ILs with low impurity levels. Additionally, we demonstrated the upscaling of the mechanochemical approach for the synthesis of Pyr₁₄TFSI from 4 g to 99 g of reagents by transitioning from ball milling to a multi-shaft planetary mechanical mixer, achieving a 97% conversion in 30 minutes. These results underscore the mechanochemical potential for practical and sustainable production of ILs, establishing this approach as a rapid and efficient route for synthesizing both hydrophilic and hydrophobic ILs.