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Abstract
The work presented in this thesis focuses on using understanding of the effects of ionic liquids on reaction outcome to rationally select the components of these solvents to achieve the desired reaction outcome.
Ionic liquids were examined as solvents for the ethanolysis of 1-fluoro-2,4-dinitrobenzene; a nucleophilic aromatic substitution process. The dependence of the rate constant on the proportion of ionic liquid in the reaction mixture was determined; the more ionic liquid present, the greater the rate constant. Activation parameters were determined for the reaction; the microscopic origin of the rate constant enhancement varied with the amount of ionic liquid present.
The components of the ionic liquids were varied and the effects on the rate constants for the abovementioned reaction were determined. When varying the cation, ionic liquids with a sterically hindered cation gave the greatest rate constants. When varying the anion, ionic liquids with a small, coordinating anion gave the greatest rate constants. The components of the ionic liquid were then rationally chosen to maximise the rate constant enhancement.
Ionic liquids were examined as solvents for the ethanolysis of 2,3,4,5,6-pentafluoropyridine, another nucleophilic aromatic substitution process. The dependence of the rate constant on the proportion of ionic liquid present in the reaction mixture was determined; the more ionic liquid present, the greater the rate constant. Activation parameters were determined for the reaction; depending on the mole fraction of ionic liquid present, the microscopic origin of the rate constant enhancement varied. Both the trends in the rate constant and their origin were similar to those observed for the ethanolysis of 1-fluoro-2,4-dinitrobenzene demonstrating solvent effects are extendable across different electrophiles.
The known effects of ionic liquid solvents on the bimolecular nucleophilic substitution reaction between benzyl bromide and pyridine were used to rationally select ionic liquids to maximise the rate constant. The rate constant enhancement here was due to ionic liquid cation – pyridine interactions. A series of ionic liquids were selected, both known and novel, in order to maximise this favourable interaction. The ‘best’ ionic liquid for this reaction type was determined based on rate constant enhancement, ease of synthesis and cost.