Room Temperature ionic liquids based on asymmetric ammonium salts

Abstract

Ionic liquids, ILs, in principle, are salts composed of weakly coordinating ions which are liquids at low temperature (˂100 0C). Room temperature ionic liquids, RTILs are those salts which are liquid even at room temperature. Due to the unique properties, such as large liquid range, negligible vapour pressure, solubility of wide range of materials and potential to be recycled and reused, ILs have become a popular class of solvents and catalysts.This study reports the synthesis of a library of asymmetric tetraalkylammonium halide salts of the form N R1R2R3R4X (where R1R2R3R4 are alkyl groups of different chain length of up to 18 C atoms and X= I- or Br-). These salts all of which are solids at room temperature, were characterised by NMR spectroscopy and elemental analysis. Through ion exchange these halide salts were converted to the analogous tetraalkylammonium bis(trifluoromethanesulfonyl)imide salts, NR1R2R3R4TFSI. All of the new TFSI based ionic liquids, with the exception of N1 2 3 4TFSI, possess melting points below room temperature and many of them showed a melting point below -40 0C. In addition to their melting points, other physical properties such as thermal behaviour, decomposition temperature, conductivities, and densities of these novel ionic liquids have been investigated. A comparison of physical properties of new RTILs synthesised in this study with the literature is also presented. The solubility of a number of salts or compounds in these asymmetric quaternary ammonium salts was investigated in order to evaluate their application as reaction media for fluorination of organic molecules. Some organic compounds and phosphorus containing salts were found to be soluble in these ionic liquids.

Date of Award	31 Dec 2013
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Alan Brisdon (Supervisor) & Robin Pritchard (Supervisor)