This thesis presents research into the binding, extraction and transport of the hexachloroplatinate anion, [PtCl6]2-, by organic receptors in a solvent extraction process. The target anion is produced during the processing of platinum-containing ores and the aim was to develop reagents that can selectively extract [PtCl6]2- to optimise the recovery of platinum. Chapter One outlines reasons for the interest in [PtCI6]2-and provides an overview of the processes and techniques used to refine precious metals. An introduction to anion coordination chemistry relevant to the research project is also presented. Chapter Two discusses the design features incorporated into organic receptors to enable strong and selective binding of [PtCl6]2-. These features include a tertiary amine protonation site, hydrogen-bond donor groups and organic solubilising moieties. The synthesis of a series of functionalised tripodal tris(2-aminoethyl)amine based receptors with sulfonamide, amide, urea, thiourea or pyrrole NH hydrogenbond donor groups are reported. Complexation reactions between the receptors and H2PtCl6 to form [(LH)2PtCl6] ion pairs are discussed. Crystallographic analysis of the [(LH)2PtCl6]complexes with TREN-based sulfonamide, urea and amide receptors confirms the presence of hydrogen-bonds between the NH donor groups and the outer-sphere of [PtCl6]2-. The low organic solubility of the complexes prevented the study of these systems in solvent extractions. Chapter Three describes the variation of terminal substituents of the tripodal receptors with the aim of improving the organic solubility of the extractants and their [PtCl6]2-complexes. In these "second generation" receptors the terminal substituents assessed include 3, 5-dimethylphenyl, 4-iso-propylphenyl, 4-tert-butylphenyl, 3, 5- dimethoxyphenyl, 3, 4 dimethoxypheynl and 3, 4, 5-trimethoxyphenyl. Through reaction of the receptors with H2PtCl6 the solubility of the resultant complexes are assessed. Chapter Four describes the development of an optimised solvent extraction method to study the extractive behaviour receptors. A pH swing mechanism is utilised to control the uptake and release of [PtCl6]2-. The extraction results for trioctylamine and the soluble tripodal urea and amide receptors are compared. Attempts are also made to confirm the stoichiometry of the complex in solution. Chapter Five describes the synthesis of tris(2-aminoethyl)amine based receptors with hydrogen- and halogen-bond donor groups with the aim of increasing the strength of the interaction between a receptor and [PtCI6]2-. Receptors with an extended tripodal scaffold based on a tris(3-aminopropyl)amine with urea and amide moieties are also presented. The results of the complexation reactions and solvent extraction studies with these modified extractants are presented. Chapter Six presents the design and synthesis of bipodal and monopodal receptors in order to assess the role of the number of hydrogen-bond donor functionalised arms. The results of the solvent extraction studies with these receptors are discussed and comparisons made between tripodal, bipodal and monopodal extractants. The crystallographic analysis of the [(LH)2PtCl6] complexes formed between the bipodal urea and amide receptors is described. Chapter Seven highlights the important findings from this work. Conclusions are drawn as to the optimum receptor system developed and this is compared to the extractant system thought to be in current use for the extraction and transport of [PtCl6]2-.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:495551 |
| Date | January 2008 |
| Creators | Bell, Katherine Jane |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/14404/ |
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