Palladium Catalyzed Hydrodechlorination of 4-Chloroanisole in Phosphonium Ionic Liquids
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AbstractUntil their production was banned in 1979, polychlorinated biphenyls (PCB’s), formed as complex mixtures, were used in electrical equipment. Although they are no longer manufactured, some PCBs are still in service—albeit, in closed or semi-closed systems such as dielectric fluids for transformers and capacitors, or are still present in the environment. The continued presence of PCBs is problematic, due to their toxicity. Their hydrophobic nature and resistance towards metabolism leads to bio-accumulation up the food chain. resulting in long term effects in chronically exposed persons, like firefighters, factory workers or persons whose food have accumulated appreciable levels of PCBs. Efficient dechlorination of polychlorinated biphenyls (PCBs) has relevance in the environment, as it would reduce the toxicity of these pollutants. The chemistry described in this thesis is a model study for dechlorinating PCBs using 4- chloroanisole as a model compound. In this fundamental study, palladium-catalyzed dechlorination of chloroanisole was studied in ionic liquids (ILs), where the catalyst was expected to be more stable than in methanol, the previously used solvent. This thesis describes the hydrodechlorination efficacy and longevity of palladium catalysts with ligands 4 (2-(di-tert-butylphosphino)biphenyl) and 5 (2-(di-tertbutylphosphino)-2 ’ ,4’ ,6’ -triisopropylbiphenyl) in methanol and ILs 6 (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), 7a (trihexyl(tetradecyl)phosphonium chloride), and 7b (trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide) (Scheme 9). Additionally, this thesis focuses on improving the logistical aspects of determining the water content in the ILs, sampling reactions to follow their progress, data reproducibility, and analysis of reaction progress, as well as the impact of water on the rate of hydrodechlorination reactions in ionic liquids. After excluding results from obviously compromised reactions, it appears that reactions in IL 7b proceed faster on average than those in IL 7a, that reactions performed with ligand 5 run faster than those with ligand 4, and that there may be a bell curve to the concentration of water vs rate of reaction, with the reaction proceeding best at intermediate water concentrations. Further experiments would be needed to confirm these results.