Developing New Inexpensive Room-Temperature Ionic Liquids with High Thermal Stability and a Greener Synthetic Profile

Ionic liquids (ILs) have advantageous physical properties, which resulted in a rapid growth of research in this area in the past 15 years. One of the biggest challenges preventing the widespread use of ILs is the cost of production due to complex synthetic routes and/or expensive starting materials. Keeping in mind these industrial needs for scale-up and the desirable properties for applications in the lubrification area, here, we report the design and synthesis of four novel series of hydrophobic room-temperature ILs (RTILs) achieved from cheap and commercially available starting materials, namely, silicon-based, imidazolium-based, phosphonium-based, and monomer imidazolium-based. These syntheses were developed as expedited chemistry protocols and possess a greener synthetic profile compared to previously reported ILs of similar structures. All the RTILs were characterized by 1D NMR (¹H NMR, ¹³C NMR, ³¹P NMR, ¹⁹F NMR, and ¹¹B NMR) and 2D NMR (COSY, HSQC, and HMBC) analyses, high-resolution mass spectrometry, and chemical tests (primarily the silver nitrate test). Preliminary thermal analysis tests by thermogravimetric analysis show all novel RTILs display remarkably high thermal stabilities (386-474 °C). Differential scanning calorimetry data show low glass transitions ranging from -36 to -72 °C, which suggests good free volume and ion mobility.