The chemistry of imidazolium salts and phosphonium-based ionic liquids

Ionic liquids represent a new technology for use in sustainable processes as solvent replacements, in catalytic reactions and electrochemical devices. Their low vapour pressure makes them potential substitutes for highly volatile organic solvents, thus reducing the amount of pollution caused through solvent evaporation and their non-flammable nature reduces the risk of fire hazard. Perhaps the most extensively studied class of ionic liquids (ILs) is based upon the imidazolium ion and these ILs have found uses in small-scale synthesis, catalysis and more recently in industrial applications. The reactivity of small molecules with imidazolium salts t hat have relevance to ILs are reported in this thesis. The imidazolium salts, a model for the imidazolium?based ionic liquids (IILs) are found to be reactive towards basic salt (silver (I) oxide), active metal (potassium), reducing agents (NaBH4) and bases such as Grignard reagents. This highlights a significant pathway of decomposition for the imidazolium ion and illustrates their unsuitability as solvents for basic reactions. Phosphonium-based ionic liquids are found to be more resistant to reactive metals and strong bases than imidazolium-based ionic liquids. These results are relevant and important because other "green" solvents, such as water, carbon dioxide and alcohols are reactive with strong nucleophiles and bases. The identification of base-resistent ILs is important since it has been suggested that more than 50% of reactions are base-catalysed.