Silylated quaternary ammonium salts – ionic liquids with hydrophobic cations†
Another class of ionic liquids was obtained by a combination of bis(perfluoroalkylsulfonyl)amide anions and O-silylated choline like cations. The protection of the hydrophilic hydroxyl group of hydroxyalkyl substituted quaternary ammonium salts with a trialkylsilyl group changes cations' properties from hydrophilic to hydrophobic; both constituents (cations and anions) of resulting ionic liquids have a hydrophobic character. Their essential physical and chemical properties were investigated. Moderate viscosity and conductivity of ionic liquids follow the Vogel-Tammann-Fulcher model of their dependency on the temperature. All ionic liquids show similar electrochemical stability as anticipated from CV measurements. The cathodic stability for most compounds is below 0 V vs. Li/Li+, and anodic decomposition starts typically over more than 5 V vs. Li/Li+. These properties suggest that these ionic liquids have potential for the preparation of electrolytes for high voltage lithium batteries.