"Click Synthesis" of Mercaptosilyl-Functionalized Ionic Liquids via Thiol-Ene Chemistry for Use as Hydrophobic Surface Coating Agents

Abstract

The thiol-ene “click” transformation described here is a high-yielding and simple fusion process, leading to a series of hydrophobic, multifunctionalized ionic liquids containing long thioether spacers (C7−C15) with low melting points and high thermal stability. The process exhibits broad scope and provides a series of imidazolium, ammonium and phosphonium-based mercaptosilyl-functionalized ionic liquids (16 examples) in excellent yields and exclusive anti-Markovnikov regioselectivity. In order to aid in defining their practical range of use in various applications, the thermophysical properties of the new ionic liquids such as glass transition temperature, decomposition temperature, viscosity and density along with their water contents, were studied. The mercaptosilane class of ILs can have important applications due to their hydrophobicity, moderately low viscosities, high thermal stabilities and wide liquids range. The synthesized ionic liquids were found to be active surface coating agents and were successfully immobilized on magnetite supermagnetic Fe3O4 nanoparticles. The representative ionic liquids with different side chains were immobilized on the surface of Fe3O4 supermagnetic nanoparticles and showed high organic loading (27.40−39.81 wt%) and low size of nanoparticles (6.72−10.12 nm). The ability to introduce trimethoxysilane into the structures of ionic liquids would open new horizons for their applications such as surface modification and hybrid materials. The incorporation of a thiol group to the structure of silane-functionalized ionic liquids could be utilized to construct novel organic-inorganic materials due to strong affinity of thiols to specific metallic surfaces.