A review of metal-mediated epoxidation is given. Jacobsen's catalyst and the
Sharpless asymmetric epoxidation catalyst are discussed. The origins of enantioselectivity
are explained using stereochemical models.
Several new salen-type ligands were synthesized based on biphenol and
binaphthol. The synthesis of these ligands and their subsequent coordination to
transition metals were described. The transition metal complexes were structurally
characterized by X-ray diffraction of single crystals. The manganese (III) complexes
were evaluated for catalytic activity in epoxidation reactions. Despite the fact that these
many of these complexes were optically active, little asymmetric induction was observed
in any of the epoxidation reactions.
The investigation of a soluble nickel salen complex for the epoxidation of olefins
led to the discovery of a new heterogeneous catalyst for the epoxidation of α,β-
unsaturated carboxylic acids. Nickel salen complexes, upon reaction with commercial
bleach, yield a fine black powder, which we identified as nickel oxide hydroxide-a
known but poorly characterized nickel peroxide containing species. The reaction of an aqueous nickel (II) source with commercial bleach also yields nickel oxide hydroxide.
This material was characterized by X-ray diffraction (XRD), transmission electron
microscopy (TEM), differential scanning calorimetry (DSC) and thermal gravimetric
analysis (TGA). Extremely broad peaks in the X-ray diffraction pattern suggested that
this material consisted of particles with a very small diameter and this was confirmed by
TEM. This insoluble material was found to function as a heterogeneous catalyst for the
epoxidation of α,β-unsaturated carboxylic acids in the presence of sodium hypochlorite.
The high activity of this catalyst in the epoxidation of certain olefins is due in part to its
small particle size, which increases the overall surface area of this heterogeneous
catalyst. Large particles of nickel oxide hydroxide were prepared and the catalytic
activity was comparatively less.
The oxidation of several other organic substrates was also explored using this
catalyst. Both primary and secondary alcohols can be oxidized with our nickel-based
system. Primary alcohols go through an aldehyde intermediate which is then in turn
oxidized to the carboxylic acid.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1746 |
| Date | 02 June 2009 |
| Creators | Grill, Joseph Michael |
| Contributors | Miller, Stephen A. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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