Stagel, K., Szpecht, A., Zielinski, D., Smiglak, M., Schnürch, M., & Bica-Schröder, K. (2022). Halide-Free Continuous Synthesis of Hydrophobic Ionic Liquids. ACS Sustainable Chemistry and Engineering, 10(34), 11215–11222. https://doi.org/10.1021/acssuschemeng.2c02871
Herein, we present a novel approach for the halide-free, continuous-flow preparation of hydrophobic ionic liquids (ILs) relying on the bis(trifluoromethanesulfonyl)imide (bistriflimide, NTf₂⁻) anion. The simple yet fast two-step synthetic route, which involves the formation of different alkyl bistriflimides (R⁴NTf₂), followed by the quaternization with an amine nucleophile, led to the desired ILs in high yields and excellent purities without any byproduct formation. The variable alkyl chain (R⁴) length and the broad range of the applicable nucleophiles (R¹R²R³N) offer considerable flexibility to the synthetic protocol. The quaternization can be performed under solvent-free conditions; moreover, the homogeneous nature of these reactions allows the application of modern continuous-flow technologies. Given these advantages, the methodology can afford not just a fast and efficient alternative for the conventional synthesis of such compounds with reduced waste water production but their negligible halide content might provide a significantly broader application range of the IL products, especially for the field of materials science.
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Project title:
Synthese neuer fluorierter ionischer Flüssigkeiten: P32882-N (Fonds zur Förderung der wissenschaftlichen Forschung (FWF))
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Additional information:
A new synthetic method for the halide-free synthesis of bis(trifluoromethanesulfonyl)imide-based, hydrophobic ILs has been developed. The simple, two-step procedure could give straightforward access to a wide variety of NTf₂ -based ILs with good yields and excellent purities. The quaternization step could be carried out under solvent-free conditions and provided high atom efficiency without additional waste formation. The reported method is intrinsically halide free, which offers many benefits for the development of new IL- based technologies that are sensitive to halide content. The overall process is significantly less time-consuming than most reported halide-free methods, and due to the reactions’ homogeneous nature, it could be successfully performed not just in the batchwise application but also in the continuous- flow operation mode. This provided an even more rapid, safe, and easily scalable synthesis of these ILs, allowing them to be obtained in high yields (86−99%) and productivity, with a residence time of 7.5 min only. The high purity renders this process not just only safe and efficient but eventually also makes the IL products suitable for a significantly broader application range, especially for materials science.
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