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Title: Catalytic dechlorination of polychlorinated biphenyls (PCBs) using new organotransition metal catalysts
Author: Fletcher, Andrew Edward David
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2007
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Abstract:
The aim of this thesis is to explore the Schwartz reaction, a method for the catalytic dechlorination of polychlorinated biphenyls (PCBs). Chapter One introduces PCBs, their stability and industrial utility, their subsequent detection in the environment and concerns over their human health effects leading to a political will for remediation 0 of PCB contaminated land. Natural, physical, biological and chemical destruction methods o for PCBs are then reviewed. The chapter concludes by introducing the Schwartz reaction which uses CP2TiCh, NaBH4 and pyridine in diglyme to dechlorinate PCBs. Its advantages and disadvantages are highlighted. Chapter Two studies the mechanism of the Schwartz reaction using a variety of techniques. A DFT study is described, reaction conditions are explored and a proposed intermediate (Cp2TiHpyr) is isolated and characterised with the aid of deuterium labelling. A Schwartz reaction using CP2TiHpyr is carried out in an EPR tube, conclusions are drawn about the Ti(III) species present therein and a modified mechanism is proposed. Chapter Three tests a variety ofnew catalysts for dechlorination ofPCBs. The original CP2TiCh catalyst is altered by variation of the ligands and the metal and other new systems containing an '(Tl-arene)FeCp' moiety are tested. New catalytic systems are presented including precursor compounds which are air and moisture stable. Chapter Four investigates the removal of toxic pyridine as a requirement for the Schwartz reaction. Alternative bases are tested and conclusions drawn about the role of the base in the mechanism. Transition metal complexes are then prepared which incorporate an amine (NMe2 or NtBu) or pyridine functionalised arm into the ligand framework. lIB NMR spectroscopy is used to observe the amine'BH3 adducts present in the reaction mixture and provide new insights into the reaction mechanism. Chapter Five explores heterogenisation of the Schwartz reaction by synthesising a range of titanocene functionalised polystyrenes. These are characterised using solid state IH NMR (MAS), TGA and EDX. These solids are then tested for their catalytic activity. Experimental procedures are documented in Chapter Six and characterising data for all new or previously uncharacterised compounds are given in Chapter Seven. Asummary of all catalytic data from Schwartz reactions in this thesis is given in Appendix One. DFT, EPR and crystal structure data are given in the Electronic Appendix.
Supervisor: Not available Sponsor: Not available
Qualification Name: University of Oxford, 2007 Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.487287  DOI: Not available
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