Thesis (Ph. D.)--University of New South Wales, 1999. / Also available online.

Thesis (M.S.)--Virginia Polytechnic Institute, 1953. / Vita. Includes bibliographical references (leaves 55-57). Also available via the Internet.

Thesis (Ph. D.)--Columbia University, 1935. / Vita. Bibliography: p. 30.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1975. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 120-132).

The project was concerned with the investigation of the electrochemical oxidation of various phenols, and to develop a viable reaction system for the production of the respective hydroquinones. Current production routes utilizing phenol as starting material have the limitations of using large amounts of acids, having to be stopped at low conversions and producing a mixture of the hydroquinones and catechols. Of the possible routes to the respective hydroquinones from the various phenols, the electrochemical oxidation of these phenols offers commercial and environmental advantages and hence formed the theme of the investigation. The synthetic possibilities proved to be more prevalent in a system when the electrochemical oxidation of these phenols was performed in an aqueous medium utilizing an organic co-solvent. Results obtained during this investigation made it possible to make certain predications about the mechanism taking place. This was found to depend on the anode material used for the oxidation. The results showed that the process developed for the electrochemical oxidation of these phenols, yields mainly the para-isomers of the respective hydroquinones and benzoquinones in good yields and selectivities, with fair current efficiencies and good mass balances at high conversions. For example: * Phenol (batch) 8 F: 345% current efficiency, 70% hydroquinone, 6% catechol, 9% benzoquinone, 9% phenol and 94 mass balance. * 2-Tert-butylphenol (flow) 10 F: 37% current efficiency, 65% hydroquinone, 33% benzoquinone, 2% phenol and 100% mass balance. * 2,6-Di-tert-butylphenol (flow) 11 F: 23% current efficiency, 92 % hydroquinone, 6% benzoquinone, 1% phenol and 99% mass balance. The developed electrochemical oxidation system offers the following advantages over previous and current methods: simplified isolation and extraction procedures, smaller amounts of acid usage, reasonably selective synthesis of the para-isomer and a less corrosive system all at high conversions.

No description available.

Polyhalogenated benzenes have been analyzed by standard electron capture chemical ionization mass spectrometry (ECCI/MS), and electron monochromator mass spectrometer (EM/MS) systems. The EM/MS experiments distinguished electronegative compounds (especially isomers) by transient negative ions (TNIs) of the same mass but differing energies and/or the formation of distinct TNIs of different masses for each electronegative compound. The ECCI/MS results of polybrominated benzenes show that "bromine addition" and hydrogen abstraction reactions occur to form ions with one to three bromines added to the starting material. Computations have given insight into the mechanisms that may be involved in the EM/MS and ECCI/MS experiments. Calculations have also provided qualitative support for the processes that may be occurring in the ECCI/MS experiments, and in non-photochemical and photochemical reactions of polyhalogenated benzenes. Photochemical experiments reveal that a minor, but notable pathway that involves an "iso-polychlorobenzene intermediate", is taking part in the photo-dehalogenation of chlorobenzene and hexachlorobenzene. / Graduation date: 2000

This thesis describes the characterization of benzene-degrading denitrifying cultures. Four objectives were pursued. The first objective was to identify conditions that promote or inhibit benzene decomposition and thus, to improve the biodegradation capacity of the cultures. FeS, resazurin, and nitrite had a detrimental impact on benzene degradation, whereas addition of supernatant from an active culture improved the benzene degradation activity by reducing the lag times. The second objective was to determine the microbial community composition in enrichment cultures and to identify the bacterial species that mediate benzene mineralization. Five dominant bacterial Operational Taxonomic Units (OTUs) were identified. The most abundant phylotype was related to the gram-positive Peptococcaceae family. Other bacteria present were closely affiliated with Dechloromonas, Azoarcus, Chlorobi and Anammox species. To correlate the growth of these specific microbes with benzene degradation, the abundance of specific 16S rRNA genes was monitored during mineralization process using quantitative polymerase chain reaction (qPCR). Based on the result of qPCR experiments and information about the metabolisms of the above bacteria, a syntrophic mode of benzene degradation was hypothesized to occur under denitrifying conditions. In this process, Peptococcaceae initiate attack on benzene, and ferment benzene to hydrogen and low molecular weight products such as acetate. These products are then consumed by nitrate-respiring Azoarcus and Dechloromonas or phototrophic Chlorobi. Anammox bacteria recycle and detoxify nitrite, and stabilize the culture. The third objective was to isolate and characterize pure cultures with the ability to mineralize benzene anaerobically. Dechloromonas- and Dechlorosoma-like microorganisms were isolated from several benzene-degrading microcosms. Theses bacteria, however, were not able to metabolize benzene anaerobically. The fourth objective was to investigate the key metabolic steps in the anaerobic benzene degradation pathway and to identify enzymes that are involved in this process. Differential transcription during growth of the culture on benzene versus growth on a metabolite of benzene degradation, i.e. benzoate was examined. Carboxylase-related genes were specifically transcribed in the presence of benzene. Furthermore, mRNA sequences corresponding to the genes that encode different enzymes of the benzoyl-CoA degradation pathway were present in the culture. These findings suggest that mineralization of benzene starts by its activation to benzoate through a carboxylation reaction catalyzed by benzene carboxylase. Benzoate is further metabolized through benzoyl-CoA pathway.

This thesis describes the characterization of benzene-degrading denitrifying cultures. Four objectives were pursued. The first objective was to identify conditions that promote or inhibit benzene decomposition and thus, to improve the biodegradation capacity of the cultures. FeS, resazurin, and nitrite had a detrimental impact on benzene degradation, whereas addition of supernatant from an active culture improved the benzene degradation activity by reducing the lag times. The second objective was to determine the microbial community composition in enrichment cultures and to identify the bacterial species that mediate benzene mineralization. Five dominant bacterial Operational Taxonomic Units (OTUs) were identified. The most abundant phylotype was related to the gram-positive Peptococcaceae family. Other bacteria present were closely affiliated with Dechloromonas, Azoarcus, Chlorobi and Anammox species. To correlate the growth of these specific microbes with benzene degradation, the abundance of specific 16S rRNA genes was monitored during mineralization process using quantitative polymerase chain reaction (qPCR). Based on the result of qPCR experiments and information about the metabolisms of the above bacteria, a syntrophic mode of benzene degradation was hypothesized to occur under denitrifying conditions. In this process, Peptococcaceae initiate attack on benzene, and ferment benzene to hydrogen and low molecular weight products such as acetate. These products are then consumed by nitrate-respiring Azoarcus and Dechloromonas or phototrophic Chlorobi. Anammox bacteria recycle and detoxify nitrite, and stabilize the culture. The third objective was to isolate and characterize pure cultures with the ability to mineralize benzene anaerobically. Dechloromonas- and Dechlorosoma-like microorganisms were isolated from several benzene-degrading microcosms. Theses bacteria, however, were not able to metabolize benzene anaerobically. The fourth objective was to investigate the key metabolic steps in the anaerobic benzene degradation pathway and to identify enzymes that are involved in this process. Differential transcription during growth of the culture on benzene versus growth on a metabolite of benzene degradation, i.e. benzoate was examined. Carboxylase-related genes were specifically transcribed in the presence of benzene. Furthermore, mRNA sequences corresponding to the genes that encode different enzymes of the benzoyl-CoA degradation pathway were present in the culture. These findings suggest that mineralization of benzene starts by its activation to benzoate through a carboxylation reaction catalyzed by benzene carboxylase. Benzoate is further metabolized through benzoyl-CoA pathway.

CCSD(T) has been used in the past to accurately predict compute the spectra and structures of small molecules. However, the large execution times required for these calculations has limited their use in larger molecules such as benzene and [10]annulene. The parallelization of analytic second derivatives of post Hartree-Fock methods, including CCSD(T), has enabled the VPT2+D treatment of the vibrational states of benzene. The fundamental frequencies and infrared active two quantum transitions that result are within 20 cm⁻¹ of the experimental values when treated for Fermi and Darling-Dennison resonances and empirical estimates for the harmonic frequencies and equilibrium bond lengths are determined to be within 12 cm⁻¹ and 0.004 Å of the values at the CCSD(T)/ANO2(fc) level of theory. The parallelization also facilitated the identification of two candidates for the structures of two isomers of [10]annulene. The harmonic frequencies of several conformations proposed in the literature were computed at the CCSD/DZP level of theory with five of the conformations being ground states. The NMR shifts of four of these structures were computed using CCSD(T)/tzp and conformation 6(C₂ "twist") was identified as the likeliest structure for one of the isomers isolated. The remaining compound was identified as conformation 2b(C₂ "boat") due to a low conformation barrier and the proximity of its average NMR shifts to experiment. The identification of both compounds rely on properties computed using analytic derivatives not entirely on the relative energies of optimized geometries. / text