The selective aerobic oxidation of organic molecules has been highlighted as a fundamental and practical challenge for modem chemistry. The oxidation of alcohols is one such challenge. It is a key reaction in the synthesis of many compounds, however rarely implemented in an industrial setting. In the last 20 years Pd(II) complexes modulated with oxidatively stable ligands have emerged as a promising class of catalysts for the reaction. Such Pd(Il) ligated complexes utilise molecular oxygen as the sole oxidant producing benign by- products such as water. Although the work to date has been pioneering, a number of challenges still need to be addressed for the reaction be industrially viable; faster rates, catalyst separation and safe handling of O2, We sought to design new catalysts initially testing a range of anionic N, O-ligands for the homogeneous Pd(II) catalysed oxidation of 2-octanol. The optimal ligand from the screen was 8-hydroxyquinoline-2-sulfonic acid (HSA), producing a TOF highly competitive with the neocuproine ligand, the current literature benchmark. Further optimisation was undertaken altering reaction parameters such as temperature, catalyst loading, base additive and the introduction of a solvent. In addition to exploring such N,O-chelating ligands we also investigated NN-chelating ligands (phenanthroline-type ligands) of neocuproine and bathocuproine disulfonic acid. Such ligands have been well documented in the literature; hence we wanted to both compare our 8-hydroxyquinoline-2-sulfonic acid ligand, as well as probing the potential for further development of such phenanthroline derivatives. In addition to a traditional solvent screen an ionic liquid solvent was undertaken. It was concluded that a more non-coordinating solvent system produced optimal rates from the (I-ISA)Pd(OAc)2 catalyst system. The influence of a CO2 atmosphere on our catalytic systems was explored throughout the thesis (with the view to a future continuous flow CO2 system/as a means for catalyst separation and recycle). In the homogenous studies the catalyst was seemingly deactivating over prolonged reaction times, presumably via catalyst aggregation. Therefore we decided to investigate Pd(II) catalysts covalently tethered to silica supports. Synthesising numerous catalysts using different functionalities, it was demonstrated that a urea linkage was the optimum functionality for our study.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:579691 |
| Date | January 2012 |
| Creators | Clendenning, Gráinne Margaret Ann |
| Publisher | Queen's University Belfast |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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