To achieve a fully reusable and reversible chemisorption system that can produce CO of high purity, the concomitant removal of reaction media should be avoided. We thus turned our attention to the use of ionic liquids (ILs), which exhibit negligible vapor pressure. ILs including Cu(I) ions have been explored as potential CO absorbents ; however, these have not yet been used as the dispersant/solvent in the desorption process, probably because ILs can occupy the pores of nanoporous materials. The dispersion of the crystalline powder of 3c in imidazolium-based IL-1 with the anion OSO2CF3 -(OTf -) (350 mg) under reduced pressure resulted in obvious improvement of the desorption to afford 2c in 90% yield (run 1, Fig. ). It should be noted that the yield of 2c was calculated via NMR analysis after the addition of THF-d8 to the resulting mixture. We experimentally confirmed that the addition of THF-d8 causes negligible changes to 2c over a short period at rt; however, after 24 h, 2c partially decomposed to give 1c•HOTf (36%) via deprotonation of the proton at the C2 position in IL-1 (Fig. ). In contrast, 3c did not show any decomposition under identical conditions. Subsequently, we explored the optimization of the desorption conditions. The use of C2methylated IL-2 with the anion NTf2 -resulted in the formation of 2c in 98% yield by preventing the aforementioned decomposition (run 2). IL-3 with the anion PF6 -also exhibited good compatibility with the applied conditions, although a slight decrease in the desorption efficiency was observed (90%; run 3). In contrast, a black precipitate was immediately generated after mixing 3c and IL-4 with the anion CH3SO4 -, and 2c was not formed (run 4). Thus, IL-2 was used in the following experiments. It should be noted that up to 2.1 ×10 -2 M of 3c can be dissolved in IL-2 at 25 °C, which corresponds to a 20% loading of 3c, while 2c shows higher solubility (6.7 ×10 -2 M at 25 °C) (Fig. ). Thus, a significant amount of solid 3c remained during the initial stage of the CO desorption, while little solid was observed after the reaction had completed, as most of the formed 2c was dissolved in IL-2 (vide infra).