Organic azides are important in the synthesis of many target molecules of great use in fine chemical and pharmaceutical production. The use of this class of compounds is however limited due to their hazardous nature and many safety concerns, as they are highly exothermic. Micro reactors can handle exotherms extremely well, due to the inherent high surface area to volume ratio, unlike the conventional batch process. This dissertation therefore aims to investigate the safe application of micro reactors in acyl azide chemistry.With this in mind, Chapter 1 provides a comprehensive background on organic azides, reaction calorimetric studies, flow chemistry technology (micro reactors) and their theoretical advantages. This chapter also discusses the preparation of organic azides in continuous flow systems and scaling up in continuous flow systems. Chapter 2 illustrates and discusses multivariate optimisation of benzoyl azide synthesis as a model reaction, synthesis of other acyl azides using the model reaction optimised conditions and multistep synthesis of carbamates, amides and amines in continuous flow systems via the Curtius rearrangement of benzoyl azide formed in situ from benzoyl chloride and sodium azide. The chapter also discusses process hazards analysis and evaluation of benzoyl azide synthesis and decomposition using calorimetric studies. It also investigates and discusses the effects of different mixing regimes and channel sizes on scale up. Chapter 3 has comprehensive experimental details for the whole dissertation with Chapter 4 providing the concluding remarks and future work recommendations.

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M.Sc. (Chemistry) / Please refer to full text to view abstract

M.Sc. (Chemistry) / Barium titanate (BaTi03) is an important material in the electronics industry as a result of its excellent dielectric properties. It has been the subject of many studies since its initial discovery, which have focussed on a wide variety of different aspects, including its synthesis, the identification of the crystal structures of its various phases, and also attempts to determine the various factors that could explain its unusual electrical properties. Since barium titanate has been studied by this wide range of disciplines, the information regarding this material is scattered over many sources. This study contains a literature survey of some of the significant work on barium titanate, in order to collect, and order, the available data into a coherent picture of the state of knowledge pertaining to the crystal structure, syntheses and electric properties of the material. From this study, it was clear that there was a distinct lack of consistent findings with respect to the identification of the tetragonal phase crystal structure. The tetragonal phase is the requisite one since it is ferroelectric, although the cubic phase also plays a significant role when the material is in the form of a very fine powder. The exact influence of the small particle size is also shown to be the object of much debate amongst the scientific community. Another area of inquiry which has attracted much attention in the past is that of the synthesis of barium titanate. The synthesis of a pure phase of barium titanate requires an intimate mixture of components which is not obtained using the standard solid-state method of synthesis, thus resulting in researchers switching to solvent-based methods of preparation. The present study also contains a summary of several of these published methods, from which four suitable methods have been selected according to certain criteria. These Criteria are that the method should be simple, use easily available materials and have been reported as having good results in terms of their dielectric properties and structural composition. It is also important that the syntheses are easy to control, to enable the extension of the work to synthesise other perovskites, poly titanates and doped barium titanate.

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D.Sc. (Chemistry) / Please refer to full text to view abstract

The presence of organic contaminants in water has caused great concern over their potential adverse health impact on humans and animals. Organic contaminants found in water are both naturally occurring and synthetic. Various chemical and physical water treatment processes are being used to remove organic contaminants. Conventional water treatment methods include the utilization of activated carbon for the removal of organic contaminants. It is generally conceded that activated carbon owes its adsorptive properties primarily to its large surface area, as well as to its pore size. Although activated carbon is nonselective against most of the water contaminants, it does not remove the concentration of organic contaminants to acceptable levels i.e. ppb. Moreover, activated carbon also absorbs moisture from the air and as a result loses its absorptive effectiveness. For this reason attention has been being given to alternative methods for water treatment especially for the removal of organic pollutants. In this study, cyclodextrin polymers that were water insoluble were synthesized and tested for their ability to remove organic species in water. Cyclodextrins (CDs) and their corresponding derivatives have been used in a wide range of applications including pharmaceutical and pesticide removal and catalysis. Cyclodextrins are cyclic oligosaccharides derived from enzyme degradation of starch. They are known as molecular hosts capable of including of forming inclusion complexes, with a degree of selectivity, with a range of guest molecules via a noncovalent interaction in their hydrophobic cavities. Although the interaction between cyclodextrin and an organic molecule is the basis for absorption or separation of various organic agents, the solubility of cyclodextrin in water and organic solvents impose limitations to the application of cyclodextrins in water treatment. Therefore, polymerizing a cyclodextrin monomer with an excess of a bifunctional linker produces an insoluble polymer which can form inclusion complexes with guest molecules. In this project, the synthesis of a number of cyclodextrin polymers was performed by reacting cyclodextrin with bifunctional linkers. / Dr. B. B. Mamba Dr. R. W. M. Krause Dr. T. J. Malefetse

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