Sasol endeavors to expand its current business through the beneficiation of commodity feedstreams having marginal value into high-value chemicals via cost-effective processes. In this regard Merisol, a division of Sasol has access to phenolic and cresylic feedstreams, which have the potential to be converted to fine chemicals. Targeted products include para-anisaldehyde, ortho- and para-hydroxybenzaldehyde which are important intermediates for the manufacture of chemicals used in the flavor and fragrance market and various other chemicals. The use of CO technology (HF/BF3) to produce these aldehydes in a two-step process from phenol as reagent is economically attractive due to the relative low cost and other benefits associated with syngas as reagent. The aim of the study was to evaluate and understand this relatively unexplored approach to the formylation of aromatic compounds. The reactivity of both phenol and anisole proved to be much lower than that of toluene. The main aldehyde isomer (para) produced in these HF/BF3/CO formylations as well as of other ortho-para directing mono-substituted benzenes tested in our laboratories were in accordance with published results. Efforts to increase substrate conversion resulted in substantial secondary product formation and mechanistic investigations showed this to be a consequence of the inherent high acidity of the reaction environment. The effect of different substituents on the relative formylation rates of benzene derivatives was investigated. These results showed that methyl groups are activating while halogens are deactivating relative to benzene as substrate. The decrease in reactivity from fluorobenzene> chlorobenzene> bromobenzene is in accordance with formylation trends observed in other acidic systems. Deuterium labeling experiments were applied to gain additional information on the formylation reaction mechanism. This study provided interesting but inconclusive results in support of the so-called intra-complex mechanism. All reported studies as well as our own work suggested that HF and BF3 in (at least) stoichiometric amounts are required for effective formylation with CO. Under these conditions this methodology for effecting aromatic formylation is not economically viable. Industrial application of formylation using CO will require the development of new catalysts or methodology to allow the use of HF/BF3 in a catalytic way. In this regard ionic liquids as a new and ecological-friendly field was explored. Chloro-aluminate ionic liquids promote the carbonylation of alkylated aromatic compounds, but fails in the case of oxygenated aromatics. Aldehyde yields of formylation in the acidified neutral ionic liquids were generally similar compared to reactions conducted in HF as solvent/catalyst. Formylation of anisole and toluene, but not of phenol in the neutral ionic liquids resulted in increased secondary product formation in comparison with hydrogen fluoride used as solvent/catalyst. This difference in behavior is not understood at present, but suggests that phenol is a good substrate for formylation in this medium, particularly with the development of a system catalytic with respect to HF/BF3 in mind. / Prof. C.W. Holzapfel
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:1984 |
| Date | 19 May 2008 |
| Creators | Willemse, Johannes Alexander |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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