Base stable and basic ionic liquids for catalysis

  • Peter McNeice

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

The use of ionic liquids for catalysis is widespread, including in industrial processes which are run on hundreds of tonnes scale. However the use of ionic liquids for basic catalysis is limited by the instability of many ionic liquids under basic conditions. We address the dual problems of ionic liquid instability under basic conditions and the lacuna of basic ionic liquids.

New quinine based ionic liquids were synthesised, including what I believe to be the first reported example of a room temperature quinine based ionic liquid. The thermal stability of all the prepared quinine ionic liquids was greater than 200 °C. Hammett basicity was relatively high for the quinine ionic liquids and the trends in thermal stability, melting point and basicity were determined to depend on the hydrogen bonding within the ionic liquid network. These ionic liquids catalysed the Knoevenagel condensation between malononitrile and benzaldehyde and were able to be recovered and reused without a decrease in activity.

More strongly basic ionic liquids were synthesised by developing a new class of binary basic ionic liquids; [Pyrr1,4][NTf2]x[OiPr]1-x. These ionic liquids were found to be stable for at least 8 months which was attributed to small concentrations of [OiPr]- , along with interion attractions and slow ion diffusion, which prevented the self-attack of [OiPr]- on the cation. [Pyrr1,4][NTf2]x[OH]1-x and [P6,6,6,6][C8SO3]x[OiPr]1-x ionic liquids were determined to be unstable.

The [Pyrr1,4][NTf2]x[OiPr]1-x ionic liquids catalysed the Knoevenagel condensation between benzaldehyde and malononitrile and also a range of aldol condensations. The ionic liquids were recovered but were unable to catalyse subsequent reactions.

Heterogenisation of [Pyrr1,4][NTf2]x[OiPr]1-x and [Pyrr1,4][NTf2]x[OH]1-x ionic liquids was achieved through the preparation of SILPS, gels, silica spheres. Heterogenisation of [P6,6,6,6][C8SO3]x[OiPr]1-x ionic liquids was achieved through the synthesis of hydrotalcite composites. The heterogeneous catalysts were used to promote Knoevenagel, aldol and dehydration reactions. The gels, silica spheres and hydrotalcite composites were recovered by filtration and re-used without a decrease in activity. Silica sphere formation was autocatalytic and I believe this to be the first reported example of this process.

Heterogeneous water purification catalysts were synthesised through the entrapment of Fe-TAML® in ionic liquid gels and ionic liquid silica spheres. These materials catalysed the decomposition of dyes in water to a similar or greater extent than homogeneous FeTAML®. The gels were reused at least 5 times without a decrease in activity which combined with their flexible preparation could possibly allow their incorporated into existing water purification infrastructure.
Date of AwardJul 2020
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsQueen's University Ionic Liquid Laboratories (QUILL)
SupervisorAndrew Marr (Supervisor), Kenneth Seddon (Supervisor) & Patricia Marr (Supervisor)

Keywords

  • Basic ionic liquids
  • Ionic liquid gels
  • Homogeneous catalysis
  • Knoevenagel condensation
  • Aldol condensation
  • Water purification
  • Heterogeneous Catalysis

Cite this

Base stable and basic ionic liquids for catalysis
McNeice, P. (Author). Jul 2020

Student thesis: Doctoral ThesisDoctor of Philosophy