With the ever increasing limitations being placed by regulations, cost and social acceptance on the processes that chemists can use to satisfy society's demands, the need to improve the control that can be exerted on reactivity and to lessen the impact of our industry has never been so prescient. As a solvent, CO2 exhibits a unique set of properties that potentially open up areas of process control that are otherwise unavailable. Due to the infancy of this technology, the impact of using CO2 in conjunction with many otherwise typical chemical processes remains relatively unexplored. Herein we present the results of utilising CO2 as a solvent for the bromination of a number of substituted benzenes and compare them to the analogous reaction in conventional solvents. The influence of CO2 on these reactions in terms of changes to regioselectivity and variation of the reaction pathways is explained with reference to Hammett δ electronic effects and the relative solubilities of the different species. The scope of the palladium carbene catalyst PEPPSI-IPr is broadened to include Heck reactions, a protocol it has shown little suitability for up to now, via an apparent in situ reduction of the pre-catalytic species by aniline. A limited amount of evidence is provided that may indicate the reactions are being catalysed by palladium nanoparticles. Finally, high pressure CO2 is explored as an antisolvent in a study designed to gather the preliminary data required to design and construct an apparatus to allow the continuous flow processing of post-reaction crude mixtures in a manner that potentially could significantly reduce the amount of waste solvent generated from chemical processing. The research presented here offers new insight into the potential of CO2 as a solvent both for reactions and for reaction processing. Additionally, the scope of a catalytic process has been expanded.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:578610 |
| Date | January 2011 |
| Creators | Barnes, Douglas Cahalane |
| Publisher | University of Leeds |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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