The separations of picoline isomers by enclathration

Master Thesis


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The chemical and physical properties of isomers make them difficult to separate using conventional methods. This renders the separation of isomers one of the more challenging obstacles in chemistry. In these cases, the supramolecular phenomenon of host-guest chemistry may be used in order to achieve separation. In this investigation, the preferences of three TADDOL (α,α,α’,α’-tetraphenyl-l,3-dioxolane4,5-dimethanol) - derived host compounds towards the isomers of methyl-pyridines (picolines) were studied. Crystals of ten novel inclusion compounds were synthesised and their structural properties were further characterised using an array of techniques. Thermal analysis was also conducted on these and other TADDOL-derived inclusion compounds. Binary competition experiments were performed with varying mole fractions of guests in the starting solution and detailed selectivity curves were generated. It was apparent that all three hosts discriminate between the picoline isomer guests. Notably, the three hosts display different preferences towards the picoline isomers and these results were rationalised by their resulting crystal structures, packing analysis, solubilities and correlated to their DSC results. DSC results showed a correlation between the thermal stability of an inclusion compound and the preference of the host towards the certain isomer involved in the inclusion complex. Further discussion on the selectivity preferences with regard to solubilities and crystal growth times was conducted.