Carbonate based ionic liquids and beyond

Ionic liquids appear almost like a different state of matter. Just like mercury, that I enjoyed playing with as a child after bursting thermometers. A liquid metal, and a liquid salt at room temperature are awe-inspiring, as their physical state is counterintuitive. We struggle to accept that a metal may not be hard, and that a salt may be non-crystalline, let alone liquid. Thus, for sheer curiosity, we started synthesising ammonium and phosphonium ionic liquids. The first hurdle was to make them efficiently, colourless and pure. And this was achieved by using dimethylcarbonate (non-toxic) instead of alkyl halides as quaternarisation reagent. These syntheses were, efficient (100% atom economic), tuneable, halide-free, and produced only CO2 and methanol as by-products.1 But, ionic liquids are not just pretty. So what can we do with them? Use them as green solvents? Sometimes yes, but often too costly, and not always an elegant or green application. Unless we can design multiphase solvent systems with other advantages.2-3 It’s might also interesting to take advantage of the chemical properties of their ions,4 or to use them as catalysts,5-6 including for the upgrade of biogenic chemicals.7 The next question might be on how these materials work, e.g. as catalysts,8 and how can these properties be monitored.9 Or whether they can be used to make new devices, e.g. based on their luminescence.10 And why not try to make old compounds, e.g. choline, by these methods? We will discuss this “genealogy” of applications and of examples, applied to a family of carbonate based ionic liquids. 1. Fabris, M.; Lucchini, V.; Noè, M.; Perosa, A.; Selva, M., Chem. Eur. J. 2009, 15 (45), 12273-12282. 2. Tundo, P.; Perosa, A., Chem. Soc. Rev. 2007, 36 (3), 532-550. 3. Gottardo`, M.`; Selva`, M.`; Perosa`, A. work in progress 4. Noè, M.; Perosa, A.; Selva, M.; Zambelli, L., Green Chem. 2010, 12 (9), 1654-1660. 5. Fabris, M.; Noe, M.; Perosa, A.; Selva, M.; Ballini, R., J. Org. Chem. 2012, 77 (4), 1805-1811. 6. Selva, M.; Noe, M.; Perosa, A.; Gottardo, M., Org. Biomol. Chem. 2012, 10 (32), 6569-6578. 7. Stanley`, J.`; Caretto`, A.`; Perosa`, A. work in progress 8. Lucchini, V.; Noè, M.; Selva, M.; Fabris, M.; Perosa, A., Chem. Commun. 2012, 48 (42), 5178-5180. 9. Lucchini, V.; Fabris, M.; Noe, M.; Perosa, A.; Selva, M., Int. J. Chem. Kinet. 2011, 43 (3), 154-160. 10. Fiorani`, G.; Selva, M.; Perosa`, A.`; Malba, C.; work in progress.