M.Sc. / The main objective of the research described in this dissertation, was the optimisation of the palladium catalysed hydroformylation of a-olefms. An evaluation of the efficiency of the palladium catalysed hydroformylation process required a comparison with the hydroformylation processes based on cobalt and rhodium. Variation of ligands (diphosphines of the size R2P(CH2)nPR2), solvents, acids, etc. had a dramatic effect on the products and the rate of the reaction. Trifluoroacetic acid was used to yield C-6 aldehydes from 1-pentene while trifluoromethanesulfonic acid yields C-11 ketones. Corresponding results were obtained with 1-octene as substrate. The length of the carbon bridge between the two phosphorous atoms has an optimum length of two in the case of alkylphosphine ligands, while an optimum length of three was found in the case of arylphosphine ligands. One disadvantage of the palladium catalysed hydroformylation reaction is that this reaction requires the use of bidentate phosphine ligands. These ligands are relatively expensive and also difficult to synthesise. The instability of the palladium complex and thus the precipitation of palladium were one of the major obstacles that had to be overcome. The use of additives not only increased the rate of hydroformylation but also increased catalyst stability, which in turn allowed an increase in the reaction temperature. This further increased the rate of the palladium catalysed hydroformylation reaction. These palladium catalysts were found to affect isomerisation of the a-olefin, but isomerisation was not a rate limiting process with respect to the hydroformylation reaction. Palladium catalysed isomerisation reactions occurred at a slower rate than the corresponding cobalt catalysed isomerisation process. However, with rhodium no isomerisation occurred. The comparison between cobalt, rhodium and palladium showed that rhodium is the best catalyst for the hydroformylation of a-olefins. The pressures and temperatures required for this process are much slower than that required for palladium and cobalt. The ligand used is triphenylphosphine, which is relatively inexpensive and non-toxic, in contrast with the more expensive ligands required for the cobalt and palladium hydroformylation processes. The use of palladium opens up the unique possibility of converting a-olefins into "dimeric" ketones, which show promise as precursors for the new class of geminidetergent
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:9742 |
| Date | 07 September 2012 |
| Creators | Ferreira, Alta |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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