Graduation date: 1994

No description available.

No description available.

No description available.

No description available.

Isoprene is the dominant non-methane organic compound emitted by vegetation into the atmosphere, with a global emission rate of ~ 500 Tg yr-1. Its oxidation serves as a major source of ground level ozone in North America during the summer months. Despite the significant impact on tropospheric chemistry, questions remain concerning the detailed oxidation mechanism. The initial step in the mechanism is the addition of OH to form four distinct isomers. The relative branching between these isomers influences the distribution of the final products. I present a comprehensive investigation into the mechanistic details of early steps in the oxidation mechanism of unsaturated hydrocarbons in the troposphere and employ theoretical and experimental techniques. To understand the detailed kinetics of the initial OH addition to unsaturated hydrocarbons, I first present a model developed for the ethylene-OH system. I present the details of a robust two-transition state model. I extend the developed two-transition state model to the case of OH addition to isoprene. Excellent agreement with observed temperature and pressure dependent rate constants affords a high confidence level in understanding of the kinetics and in the calculated branching ratio of the initial OH addition step. I then focus attention on the subsequent reactivity of the OH-isoprene adducts. Until recently, all four of the OH-isoprene adducts were supposed to have reacted with O2 via addition to form alkylperoxy radicals. Previous computational results suggest that two of the OH-isoprene adducts undergo an intramolecular cyclic isomerization followed by hydrogen abstraction by O2 to form stable carbonyl compounds. I have synthesized photolytic precursors, presenting a novel approach to probe the subsequent reactivity of individual hydroxyalkyl radicals. Initial verification of the cyclic isomerization pathway involved synthesis of the photolytic precursor corresponding to the 1,3-butadiene-OH adduct. A culmination of theoretical and experimental techniques allowed verification of the cyclic isomerization pathway. I synthesized the photolytic precursor, which provided a single isoprene-OH adduct. Employing laser photolysis/laser induced fluorescence, time-dependent multiplexed mass spectrometry, velocity map ion imaging, and theoretical techniques, we present the full characterization of the reactivity of the single isoprene-OH adduct in the presence of O2.

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.

Meat lipid oxidation causes negative quality effects, especially in further processed products. Butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and rosemary extract (RM) are common antioxidants, but plant-based tannin compounds have been shown to be effective antioxidants. The objective was to evaluate antioxidant effectiveness, pH, color, and sensory effects of several tannin sources. In study 1, 19 percent fat ground beef was mixed with no treatment (control), BHA/BHT (0.02percent), RM (0.2percent), or 0.25percent or 0.5percent powders of Chardonnay grapeseed (CG), Norton grapeseed (NG), CitruSmart (CS), or dried cherry (CP). Raw and cooked patties were aerobically stored for 0 to 5 days at 4 degrees C. Cooked patties were analyzed using the TBARS (thiobarbituric acid reactive substances) method. Raw patties were analyzed for pH, instrumental color, subjective color, and ingredient specks. Study 2 was similar, except the treatments were 0.25percent and 0.5percent powders of CG, chestnut (CN), mimosa (M), and quebracho (Q) tannins, as well as 0.5percent NG, 0.02percent BHA/BHT, 0.2percent RM, and a control. In study 1, only the NG and CG pre-cooked patties had similar or lower TBARS values compared to RM and BHA/BHT patties. All tannin treatments, except 0.25percent CG and 0.25percent CS, lowered pH compared to the control. Patties with NG and 0.5percent CG were darker, and tannin-treated patties were not redder than the control. Patties with CG and 0.5percent NG were less yellow. Subjectively, tannin-treated patties did not have less discoloration during storage, and the CG and NG patties had numerous visible ingredient specks. In study 2, CN, M, Q, and 0.5percent CG treated patties had low TBARS during storage. pH was slightly lower in CG and CN patties than the control. All tannin-treated patties were darker than the control patties, except patties containing 0.25percent CG and Q, and control patties had the highest red values. Tannin-treatments patties, except CN and Q patties, were less yellow. Subjectively, only 0.25percent M patties had less discoloration than control patties, while 0.5percent CN patties were more discolored. Norton and Chardonnay grapeseed flour and chesnut, mimosa, and quebracho powders would be recommended for pre-cooked ground beef patties based on their antioxidant effectiveness in these studies.

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