Homogeneous oxidation catalysis in multiphasic liquid solvent systems

Carrying out oxidations on an industrial scale in an environmentally sustainable manner can be challenging with currently available methods. Consequentially, the pharmaceutical industry avoids transformations involving oxidations where possible. Developments over the past few decades have brought catalytic processes to light that can carry out oxidations using simple terminal oxidants, such as O2 and H202• In particular, ligand-promoted Pd(II) complexes have been shown to be capable of oxidising alcohols and olefins to carbonyl compounds, producing water as the principal byproduct. In this thesis, aerobic alcohol oxidations and Wacker-type olefin oxidations are studied, with the aim of minimising Pd catalyst loadings through the stabilisation of the catalyst using ligands. Continuing on from previous work on aerobic alcohol oxidations promoted by the 8-hydroxy-2- quinolinesulfonic acid (HSA) ligand, study of functionalized imines and NHC ligands shows the uniqueness of the HSA ligand in enhancement of the oxidation of 2-octanol to 2-octanone. In [C4mpyrr] [FAP] the HSA complex was seen to deactivate but Pd-black was not seen to form, suggesting that the ionic liquid is stabilising the formation of Pd nanoparticles. Supporting of the HSA complex on a SILP was shown to provide similar catalytic activity as in the bulk phase, but requiring significantly smaller volumes of ionic liquid to function. For the Wacker oxidation of olefins, cationic triflate Pdll-complexes were investigated in weakly coordinating solvents, which were found to be active catalysts in a pressurised 8% O2 in N2 environment but resulted in rapid olefin isomerisation. A Pd(OAc)2/H202,-mediated oxidation system in acetic acid was then developed, promoted by the use of ligands such as 2-(2'-pyridyl)benzoxazole. The catalyst could yield 69% acetophenone from styrene under room temperature conditions in 24 hours. Also, the concept of a thermally phase switchable betainium ionic liquid/H2O solvent was trialed for the simplified recovery of the product and catalyst recycle post-reaction.