- Title
- Investigation of the potential separation of isomers and related compounds using host compound (2R,3R)-(−)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol
- Creator
- Pohl, Pieter Lourens
- Subject
- Chemistry, Organic
- Subject
- Clathrate compounds Thermal analysis
- Date Issued
- 2018
- Date
- 2018
- Type
- Thesis
- Type
- Doctoral
- Type
- DPhil
- Identifier
- http://hdl.handle.net/10948/23131
- Identifier
- vital:30432
- Description
- In this study, we investigated the potential of a host compound, (2R,3R)-(−)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (DMT), for use in the separation of isomers and related compounds using host-guest chemistry. The title molecule, DMT, is composed of a butane chain bearing hydroxyl moieties on the terminal carbons and methoxy moieties on the two internal, chiral carbon atoms. In addition, there are two phenyl rings on each of the terminal carbons. The synthesis of DMT was carried out by subjecting the diester of naturally-occurring optically active tartaric acid to a Grignard reaction employing phenylmagnesium bromide. Subsequent methylation of the secondary hydroxy groups with dimethyl sulfate afforded DMT. The resulting host molecule was investigated for its inclusion abilities by crystallizing with a number of potential aromatic, aliphatic and alicyclic guests such as toluene, aniline, nitrobenzene, anisole, cyclohexane, ethyl acetate and ethanol. Host:guest ratios were determined by means of 1H-NMR spectroscopy. Of the hosts investigated, DMT favoured a host:guest ratio of 2:1 for all included guests investigated. It complexed with most non-polycyclic aromatic guests as well as cyclohexane, cyclohexene and cyclohexanone. It was not able to include short chain or branched alcohols such as methanol, ethanol or 2-propanol, or other hetero-aliphatic or hetero- cyclic compounds such as diethyl ether, acetonitrile, morpholine or dioxane. Competition inclusion experiments were performed in which DMT was crystallized from equimolar and non-equimolar binary, ternary and quaternary mixtures of appropriate guests. The mother liquor mixtures and resultant crystals were subjected to GC-MS analysis in order to determine whether DMT showed discriminatory behaviour towards the guests from a mixture. It was observed that DMT was able to differentiate between related compounds, for example, the host preferred to include N,N-dimethylaniline compared with N-methylaniline and aniline. The host also discriminated against isomers, for example, p-xylene was preferentially included over o-xylene and m-xylene, while o-cresol was included in preference to p-cresol and m-cresol. Single crystal X-ray analysis was used to investigate the host–guest interactions responsible for guest inclusion, as well as to discern reasons for the host’s selective behaviour. X-ray data for the inclusion complexes indicated that each complex was isostructural, crystallizing in the monoclinic C2 crystal system. A pair of 1,3- and 2,4- intramolecular hydrogen bonds, as well as intramolecular non-classic hydrogen bonds between adjacent ortho-aromatic hydrogens and hydroxy moieties was a significant stabilizing factor for the geometry of the host. Guests were held within discrete cavities in the crystal lattice, and experienced only π–π stacking, CH–π interactions and other short contacts. Thermal analyses were used to determine the relative thermal stabilities of the complexes, and these data compared to the selectivity preference of DMT, obtained from the competition experiments, in order to assess the reasons for any discriminatory behaviour. Finally, Hirshfeld surface analysis data was used to determine if the thermal stability of the complexes was related to the number and type of interactions between host and guest.
- Format
- xiii, 314 leaves
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
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