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Polyunsaturated omega-3 fatty acids (n-3 PUFAs) have been suggested to reduce risk for multiple diseases but animal studies on the beneficial effects of n-3 PUFAs are conflicting, possibly due to the presence of toxic lipid oxidation products in the oils used in these studies. In order to provide guidance for future research in n-3 PUFA supplementation, this study researched lipid oxidation and its inhibition in an animal feed system enriched with fish oil. Different storage conditions were tested, and it was found that samples stored at room temperature or above were at significant risk for oxidation with lag phases of propanal formation being 56, 8 and 2 days at 4°C, 23°C and 37°C. More than 65% removal of oxygen was needed to significantly decrease lipid oxidation. Greater than 65% removal of oxygen could be achieved in less than 1 minute of nitrogen flushing. Tocopherols were not strong antioxidants in the animal feed but Trolox was, suggesting that the fish oil enriched rodent feed acts similarly to bulk oil. Both ascorbic acid and ascorbyl palmitate were found to be ineffective, possibly due to their prooxidant activity. In a comparison of propyl gallate (PG), butylhydroxy toluene (BHT), and tert-butylhydroquinone (TBHQ), results were found similar to other low-moisture systems, with PG being prooxidative, BHT improving lag phase, and TBHQ having a significant impact on lag phase. These results suggest that lipid oxidation products can be present at the start of a dietary omega-3 fatty acid study if poor quality oils are used and that oxidation can occur in the feed during storage times common to animal studies. These findings indicate that researchers should use antioxidant strategies to control oxidation in animal feeds to avoid potentially conflicting effects of lipid oxidation products in dietary omega-3 fatty acid studies.

The kinetics for the reaction of the oxidation of acetaldehyde by chromic acid in aqueous medium has been studied in an attempt to extend the present knowledge of oxidation by chromic acid. In particular, these experiments were undertaken in order to see if there are any similarities between this reaction and the oxidation of isopropyl alcohol in aqueous medium, which other investigators have studied. The main runs were carried out at 25°, at an ionic strength of 0.3. The reaction was followed by the decrease in chromic acid concentration as determined with the Beckman Spectrophotometer. In all of the runs, the concentrations of acetaldehyde and H⁺ were in excess of the chromic acid concentrations. It was found that the oxidation of acetaldehyde is first order in acetaldehyde and first order in HCrO₄⁻, (but not strictly first order in total chromic acid). The reaction is roughly second order in H⁺. Mn⁺² has an inhibitory effect upon the rate, as has been found in the isopropyl alcohol oxidation. Because of the similarity in kinetic behavior between acetaldehyde and isopropyl alcohol, the mechanisms are probably very similar. This mechanism for acetaldehyde oxidation has been discussed in some detail. / Master of Science

The dehydration of isopropanol over anodic oxides was studied. The catalytic activity of the anodic oxides prepared in phosphoric, sulfuric, and oxalic acid was compared to the activity of ν-Al₂O₃. The effect of various thermal treatments on the catalytic activity was examined. IR spectroscopy proved useful for the study of the effect of thermal treatment on the acidity of the oxides. X-ray photoelectron spectroscopy (XPS) was employed to examine the oxide surfaces both before and after use as a catalyst. The acidity of the oxides was studied by various methods and related to the activity of the oxides. The acidity of the oxide surfaces was studied by the adsorption of pH indicators on the oxide surfaces. The adsorption of gaseous bases, ammonia and pyridine, was studied by IR spectroscopy and temperature programmed desorption mass spectrometry. It was thus possible to differentiate between Lewis and Brønsted acid sites and to determine the quantity of the acid sites on the various oxides. / Ph. D.

Master of Science / Department of Chemical Engineering / James H. Edgar / Silicon oxidation has been the cornerstone of the semiconductor industry for many years, so understanding and being able to predict the oxidation process is paramount. The most popular model to date is the Deal-Grove model for the thermal oxidation of planar silicon surfaces. The Deal-Grove model owes its popularity to the overall simplicity in which it was derived and the accuracy in which it predicts the oxidation of planar silicon geometries. Due to this popularity and accuracy it is desirable to extend the Deal-Grove model beyond flat surfaces to other geometries such as cylinders and spheres. Extending the Deal-Grove model to these types of geometries would allow the prediction of the oxidation of silicon nano-wires and silicon nanocrystals. Being able to predict the oxidation is attractive due to the recent progress of integration of silicon nano-wires and silicon nano-crystals into microelectronic devices. Prediction of the oxidation of silicon cylinders (nano-wires) and spheres (nano-crystals) by simply utilizing the established planar Deal-Grovel model results in highly exaggerated oxide thicknesses compared with empirical data. This exaggeration for small silicon cylinders and spheres is due to the effects of the reduction in the available surface area for oxidation along with the stress induced due to the volumetric expansion and viscous flow of the oxide on non-planar surfaces. These stress effects retard the oxidation rate in non-planar silicon geometries with respect to flat surfaces. This reduction in the oxidation rate reduction is caused by the normal compressive stress which is normal to the SiO[subscript]2/Si interface due to the volumetric expansion during oxidation. This compressive stress reduces the reaction rate constant at the SiO[subscript]2/Si interface and thus retards the overall oxidation rate for silicon cylinders and spheres with respect to planar silicon. The focus of this paper will be to contrast cylindrical and spherical versions of the Deal-Grove model to the well established planar version. Surface area and stress effects will also be explored as they help explain the reduction in the oxidation rate for non-planar silicon geometries.

This research has been directed at the study of neighboring group participation in electrooxidation of thioethers. Controlled potential oxidation of substituted 1,3-dithiane in wet acetonitrile provides substituted 1,2-dithiolane 1-oxide in good yield. Thioethers appended with neighboring alcohols and carboxylate are catalytically oxidized in a redox cycle by bromide ion. The formation of the alkoxysulfonium salt intermediates in such reactions is confirmed by product study. On the other hand, the acyloxysulfonium salt intermediates in the electrooxidation of endo -6-methylthio-bicyclo [2.2.1] heptane-2- endo -carboxylic acid (1) are unstable at room temperature. Control experiments using ¹⁸O labeled compounds prove unequivocally the existent of the acyloxysulfonium salt intermediates. Diastereospecific oxidation of 1 and its methyl ester with DABCO.2Br₂ complex and m-CPBA is sterically controlled. In both cases, similar product ratios are observed which is explained by the participation of the carboxylic acid group in the case of DABCO.2Br₂ oxidation but not in the case of m-CPBA oxidation. The structure of one of the diastereomer of the endo acid sulfoxide is unequivocally proved by x-ray crystallographic analysis.

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The partial oxidation of methanol to formaldehyde with air as oxidant has been studied with supported monometallic and bimetallic catalysts of copper and silver over a range of temperature and contact times. This was done to investigate the influence the bimetallics could possibly have on either the reaction pathways and/or the product(s) selectivity of the oxidation of methanol. Characterisation of these catalysts was performed by nitrogen adsorption and porosity measurements, XRD, and IR spectroscopy of adsorbed methanol and of adsorbed CO. These results indicated no crystalline phases of the loaded metals to be present. CO adsorption showed the presence of small cluster metal atoms on the surface of the catalysts. The reduction peaks from TPR also revealed the presence of partially oxidised and dispersed metal atoms. Infra-red studies of methanol adsorbed on these sample catalysts revealed the presence of intermediate methoxy and formate species which are believed to be formed in the course of the reactions. Results showed the monometallic copper and silver catalyst to be more active than the bimetallics. Although formaldehyde selectivities and yields were generally low, they were highest for the bimetallics supported on the silica catalyst than the monometalics and alumina supported samples. Copper-silver interaction in the bimetallic was proposed to enhance the reduction of the silver that enhanced the selectivity to formaldehyde. In particular under conditions, low conversions of methanol saw highest selectivities to formaldehyde. There was also a pronounced effect of the supports on product distribution and activities with the alumina based samples being more active than the silica supported ones, with the product distributions on the alumina supported significantly showing high yields of DME while the silica showed high yield for methyl formate with COx and CH4 detected in small quantities on all the catalysts within the parameters investigated.