FACULTY OF SCIENCE Halogen-free synthesis of 1,3-dialkylimidazolium ionic liquids Arne VAN DEN BOSSCHE Supervisor: Prof. Dr. Koen Binnemans Thesis presented in fulfillment of the requirements Co-supervisor: Prof. Dr. Wim Dehaen for the degree of Master of Science Mentor: Drs. Daphne Depuydt in Chemistry Academic year 2014-2015 © Copyright by KU Leuven Without written permission of the promotors and the authors it is forbidden to reproduce or adapt in any form or by any means any part of this publication. Requests for obtaining the right to reproduce or utilize parts of this publication should be addressed to KU Leuven, Faculteit Wetenschappen, Geel Huis, Kasteelpark Arenberg 11 bus 2100, 3001 Leuven (Heverlee), Telephone +32 16 32 14 01. A written permission of the promotor is also required to use the methods, products, schematics and programs described in this work for industrial or commercial use, and for submitting this publication in scientific contests. Table of contents Dankwoord .............................................................................................................................. i Abstract .................................................................................................................................. ii Samenvatting ........................................................................................................................ iii Summary ................................................................................................................................ v Thesis outline ....................................................................................................................... vii List of abbreviations ............................................................................................................ viii 1 Literature study .............................................................................................................. 1 1.1 Ionic liquids ............................................................................................................. 1 1.1.1 Definition .......................................................................................................... 1 1.1.2 History of ILs .................................................................................................... 1 1.2 Imidazoles ............................................................................................................... 3 1.2.1 Aromaticity ....................................................................................................... 3 1.2.2 Synthesis ......................................................................................................... 4 1.3 Imidazolium ............................................................................................................. 7 1.3.1 Protonation of imidazoles ................................................................................. 7 1.3.2 Quaternization of imidazoles ............................................................................ 7 1.3.3 Direct imidazolium synthesis ............................................................................ 8 1.4 Metatheses ............................................................................................................. 8 1.4.1 Anion alteration ................................................................................................ 9 1.4.2 Anion metatheses ............................................................................................ 9 1.4.3 Anion exchange resins (AER) .........................................................................10 1.5 Properties of imidazolium ionic liquids ....................................................................12 1.5.1 Vapor pressure ................................................................................................12 1.5.2 Melting point ....................................................................................................13 1.5.3 Viscosity ..........................................................................................................15 1.6 Temperature-dependent miscibility of imidazolium ionic liquids with water .............16 1.6.1 Introduction .....................................................................................................16 1.6.2 IL-water mixtures with UCST behavior ............................................................18 1.6.3 IL-water mixtures with LCST behavior .............................................................19 1.6.4 Thermomorphic behavior of ILs with organic solvents .....................................19 1.6.5 Targeting thermomorphic imidazolium ILs .......................................................20 2 Used techniques............................................................................................................21 2.1 Nuclear Magnetic Resonance Spectroscopy ..........................................................21 2.2 Attenuated Total Reflectance - Fourier Transform Infrared Spectroscopy ..............22 2.3 Electrospray Ionization Mass Spectrometry ............................................................22 2.4 CHN analysis .........................................................................................................23 2.5 Coulometric Karl Fischer Titration ..........................................................................24 2.6 Viscosimetry ...........................................................................................................25 2.7 Differential Scanning Calorimetry ...........................................................................25 2.8 Thermogravimetric Analysis ...................................................................................26 3 Health, safety & environment (HSE) ..............................................................................27 4 Synthesis of imidazolium ionic liquids ............................................................................28 4.1 Synthetic goals .......................................................................................................28 4.1.1 Introduction .....................................................................................................28 4.1.2 Imidazolium synthesis .....................................................................................28 4.1.3 Metathesis reactions .......................................................................................28 4.2 Imidazole synthesis ................................................................................................29 4.2.1 Debus-Radziszewski reaction .........................................................................29 4.3 Imidazolium synthesis ............................................................................................32 4.3.1 1,2,3-Trisubstituted imidazolium ......................................................................32 4.3.2 1,3-Dialkylimidazolium .....................................................................................33 4.3.3 1,3-Dialkylimidazolium acetate ........................................................................37 4.3.4 Large 1,3-dialkylimidazolium acetate batches .................................................40 4.3.5 1,2,3-Trisubstituted imidazolium acetate .........................................................43 4.4 Metatheses ............................................................................................................46 4.4.1 Different strategies for metathesis ...................................................................46 4.4.2 Bis(trifluoromethylsulfonyl)imide ......................................................................48 4.4.3 p-Toluenesulfonate .........................................................................................52 4.4.4 Bis(2-ethylhexyl)phosphate .............................................................................57 4.4.5 Nitrate .............................................................................................................60 5 Results and discussion ..................................................................................................65 5.1 Imidazolium synthesis ............................................................................................65 5.1.1 Enolizable products .........................................................................................65 5.1.2 Halogen-free synthesis of 1,3-dialkylimidazolium ............................................69 5.2 Metatheses ............................................................................................................74 5.2.1 Decisive parameters........................................................................................74 5.2.2 Successful conditions for metatheses .............................................................74 5.3 Properties of ionic liquids........................................................................................75 5.3.1 Color ...............................................................................................................75 5.3.2 Water content ..................................................................................................75 5.3.3 Viscosity ..........................................................................................................76 5.3.4 Melting point ....................................................................................................80 5.4 Thermomorphic behavior........................................................................................80