Ionic liquids (ILs), consisting of ions that are liquid at ambient temperatures, can act as solvents for a broad spectrum of chemical processes. These ionic liquids are attracting increasing attention from industry because they promise significant environmental as well as product and process benefits. ILs were used as solvents for two industrially important homogeneous reactions namely metathesis of 1-octene and the hydroformylation of vinyl acetate. In the metathesis of 1-octene, several reaction parameters were investigated, including temperature, catalyst (type and concentration) and influence of ionic solvent and conventional solvents. Temperature and catalyst concentration were found to be rate-determining factors, but played smaller roles in determining the outcomes of the reactions compared to the influence of individual ILs. It was discovered that more polar ILs were favourable in producing high rates and selectivities. Imidazolium-based cations and tetrafluoroborate anions were superior in activity when compared to other combinations of cations and anions. The addition of catalyst promoters such as phenol and tin(II) chloride were also investigated and found to enhance metathesis rates in “neat” reactions. These catalyst promoters inhibited metathesis rates when used in combination with ILs. In the hydroformylation of vinyl acetate, several reaction parameters were investigated, including temperature, catalyst concentration, vinyl acetate concentration, ligand concentration, syngas pressure and influence of ionic solvent and conventional solvents. It was shown that high n : i ratios of aldehyde products were formed with specific IL systems. Also, low ligand concentrations and low vinyl acetate concentrations increased selectivities, although rates of reactions were somewhat compromised. Lower syngas pressure and lower temperatures afforded enhanced selectivities, again at the expense of reaction rates. Depending on whether fast reaction rates or high regioselectivity is required, the IL and general reaction conditions can be tailored to fit the needs of the reaction. It was discovered that aromatic-containing ammonium-based ILs v afforded high rates at low selectivity. Bulkier ammonium cations tended to give lower rates but the selectivity was significantly enhanced. Impurities present in ILs have also been shown to have a marked effect on hydroformylation rates and selectivity. The reader will be accompanied along a path designed to discover an optimised set of reaction conditions, the path of which will take the reader from reactions providing low selectivities, low turnover numbers and low yields to a much brighter picture, namely extremely high selectivities, turnover numbers and yields. / Prof. D.B.G. Williams
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:6893 |
| Date | 06 May 2008 |
| Creators | Ajam, Mariam |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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