Philosophiae Doctor - PhD / In this thesis typical homogeneous and dendritic immobilized catalysts derived from
salicylaldimines were investigated as catalysts for the oxidation of hydrocarbons using
hydrogen peroxide as oxidant under aerobic conditions. This research work thus describes
the synthesis of several new N-(aryl)salicylaldimines as well as peripheral functionalised
salicylaldimine poly(propyleneimine) dendrimers. The dendritic ligands were obtained by
modifying the peripheral groups of Generation 1 and Generation 2 poly(propyleneimine)
dendrimer, (DAB-(NH2)n) which are commercially available. Both types of ligands were
utilized to synthesize Cu(II) and Co(II) complexes using appropriate acetate salts. The
ligands systems and metal complexes prepared were fully characterized using a range of
physical techniques. The Cu(II) and Co(II) complexes were evaluated as catalysts for the oxidation of phenol
and cyclohexene using hydrogen peroxide as oxidant under an oxygen atmosphere. The
catalytic oxidation of phenol to the dihydroxybenzenes, catechol (CT) and hydroquinone
(HQ), was investigated in aqueous media at various pH values. All the complexes
investigated were active for the hydroxylation process producing CT as major product. The
pH of the reaction medium was found to have much more of an influence on the activity
and product selectivity of the Co(II) complexes as compared to the case for the Cu(II)
complexes. All the catalysts investigated were also found to exhibit good activity for the oxidation of cyclohexene producing predominantly the allylic oxidation products 2-cyclohexene-1-one and 2-cyclohexene-1-ol. However the formation of the epoxide, cyclohexene oxide was
also observed as minor product or in trace quantities. It was found that the cobalt catalysts
produced 2-cyclohexene-1-one as major product, however higher levels of 2-cyclohexene-
1-ol was produced by all catalysts in catalytic runs where the oxidant to substrate ratio was
reduced and when the metal loading was increased. In the case of the copper catalysts 2-
cyclohexene-1-ol was produce in slightly higher levels than 2-cyclohexene-1-one.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uwc/oai:etd.uwc.ac.za:11394/3427 |
| Date | January 2009 |
| Creators | Van Wyk, Juanita Lizélle |
| Contributors | Mapolie, S. F. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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