Thesis (doctoral)--Lund University, 1998. / Added t.p. with thesis statement inserted. Includes bibliographical references.

Thesis (doctoral)--Lund University, 1998. / Added t.p. with thesis statement inserted. Includes bibliographical references.

Thesis (Ph. D.)--University of Nebraska, 1930. / Bibliography: p. 31-32.

Chiral phosphoric acids are bifunctional catalysts that have the ability to activate electrophiles and nucleophiles through hydrogen bonding, and they have been successful in catalysing highly enantioselective additions of a wide range of nucleophiles to imines. In most literature reports it is not frequently revealed how these catalysts impart enantioselectivity. Thus, the vast majority of time required for reaction development is expended on the optimisation of the catalyst features. The research described here explores the ability of relating computational derived catalyst parameters to enantioselectivity as a means to assess the catalyst features important for enantioinduction. The proposed features are evaluated computationally and summarised into simple qualitative models to understand and predict outcomes of similar reactions. In Chapter 1, I provide an overview of the progress and challenges in the development of chiral phosphoric acid mediated reactions. I highlight leading computational studies that have enabled a greater understanding of how the catalyst imparts reactivity and selectivity. In general, the studies focus on the most effective catalyst and do not do a detailed investigation into the effects of changing the substituents at the 3,3’ positions. Implicating steric effects from reasonably large groups as a key component in imparting enantioselectivity. However, it is clear that they have a more subtle effect. A large group is required but if it is too large poor or unusual results are obtained, making the correct choice of reaction conditions challenging. In Chapter 2, I develop a quantitative assessment of the substituents at the 3,3’ positions. I show in Chapters 3 and 4 that I can use rotation barriers in combination with a novel steric parameter, AREA(θ), to correlate enantioselectivity. By exploiting this finding, the catalyst features important for enantioselectivity can be identified, and this is validated by QM/MM hybrid calculations. Summarising these detailed calculations into a single qualitative model, guides optimal catalyst choice for all seventy-seven literature reactions reporting over 1000 transformations. These mechanistic studies have guided the design of a new catalyst with increased versatility, which is discussed in Chapter 5. Chapter 6 details my study into the effect of the hydroxyl group on the mechanism of transfer hydrogenation of imines derived from ortho-hydroxyacetophenone. I show, using detailed DFT and ONIOM calculations, that transition states of these reactions involve hydrogen bonding from both the hydroxyl group on the imine and the nucleophile’s proton to the phosphate catalyst. In Chapter 7, computational analysis is used to provide insight into the origins of enantioselectivity in chiral phosphoric acid catalysed Friedel-Crafts and Mannich reactions proceeding through monoactivation mechanisms. The final chapter contains an in-depth look into the stereoelectronic effects altering enantioselectivity in the silver-phosphate mediated spirocyclisation reaction involving aromatic ynones. In this study I show that enantioselectivity is governed by the non-covalent interactions between the aromatic group of the ynone and the 3,3’ substituent. I was able to propose synthetic modifications to the substrate used in this reaction, resulting in an improvement in enantioselectivity.

Made available in DSpace on 2014-10-09T12:31:52Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:09Z (GMT). No. of bitstreams: 1 02245.pdf: 2619284 bytes, checksum: 920d3ab52801f80334d14ea5aa1bf92b (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Este trabalho aborda a caracterização da matéria orgânica existente num ácido fosfórico de pureza industrial (AFPI), oriundo do Marrocos, objetivando sua remoção através de flotação por ar dissolvido (FAD). O AFPI é um líquido escuro que exibe densidade (2020 kg/m³) e viscosidade dinâmica (1,94 x 10-² Pa.s at 20°C) muito mais alta do que os tipos mais puros de ácido fosfórico, como o grau alimentar e o de pureza analítica. Por outro lado, o AFPI apresenta tensão superficial mais baixa que o ácido de grau alimentício (55,2 mN/m versus 63,7 mN/m a 25°C), indicando a presença de espécies surfactantes dissolvidas (ácidos carboxílicos de cadeia aromática). O teor de 447ppm de carbono orgânico total (TOC) evidencia a alta contaminação do AFPI marroquino por matéria orgânica, que pode ocorrer dissolvida (ácidos carboxílicos aromáticos) ou na forma de minúsculas placas que exibem diâmetro (média aritmética ponderada) de 4µm. Ensaios FAD foram executados usando ar pressurizado a 3,5kgf/cm², que após alívio de pressão, produziu uma população de bolhas com diâmetro de 2,41 x 10`POT´-5m (média aritmética ponderada) e altíssimo desvio padrão (2,94 x10`POT´-5m). A medida do diâmetro de bolhas (db), através de difração de laser, somente foi factível com mistura contendo 40% de ácido fosfórico grau alimentar e 60% de água. Devido a isto, os valores reais de db nos ensaios FAD podem diferir os valores medidos. Ensaios DAF foram executados sob diferentes tempos de flotação (15-60 minutos), todavia a mais alta remoção de TOC (somente de 17,7%) foi obtida com 45 minutos de flotação. A remoção muito baixa de TOC (e também de As, Mg e sulfato) gerada pelos ensaios FAD pode ser explicada pela baixa eficiência de colisão (EC) exibida por minúsculas placas (partículas orgânicas suspensas no AFPI) que precisam colidir com bolhas de ar muito maiores para que possam aderir às mesmas, flutuar e serem removidas do AFPI. Esta possibilidade foi corroborada por um valor de EC da ordem de 0,04 (EC~0,04), que foi determinada pelo modelo de Yoon-Luttrell. / This thesis approaches the characterization of the organic matter which exists in a Moroccan phosphoric acid of industrial grade (PAIG), aiming at its removal via Dissolved Air Flotation (DAF). PAIG is a dark liquid which exhibits specific gravity 2020 kg/m³ (26°C) and dynamic viscosity 1.94 x 10-² Pa.s (20°C) very much higher than other purified types of phosphoric acid (food or analytical grade). Conversely it presents surface tension lower than phosphoric acid food grade (55.2 mN/m versus 63.7 mN/m at 25°C), indicating the presence of dissolved surfactants (carboxylic acids bearing aromatic chains). The content of 447ppm of total organic carbon (TOC) evidences its high contamination by organic matter, which may occur either as dissolved species (aromatic carboxylic acids) or suspended platy-shaped particles (weighed average diameter of 4Êm). DAF experiments were conducted using an air pressurization of 3.5kgf/cm², which, after pressure release, yielded a bubble swarm of weighed average size of 2.41 x 10-5m and a large standard deviation of 2.94 x 10-5m. Because bubble size (db) measurements were conducted via laser diffraction with a mixture of 40% phosphoric acid food grade plus 60% of water, actual values of db may be different from the measured ones. DAF tests were conducted under different length of time (15-60 minutes), but the highest removal of TOC (17.7%) was accomplished at 45 minutes of flotation time. The very low removal of TOC (and also Mg, As and sulfate) yielded by DAF experiments may be explained by a low efficiency of collision (EC) exhibited by small platelets (suspended organic particles) which must collide with bigger air bubbles in order to attach to them and be floated. This possibility was corroborated by efficiency of collision (EC) = 0.04, determined by Yoon-Luttrell Model.

Made available in DSpace on 2014-10-09T12:31:52Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:09Z (GMT). No. of bitstreams: 1 02245.pdf: 2619284 bytes, checksum: 920d3ab52801f80334d14ea5aa1bf92b (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

The performance of a phosphoric acid fuel cell reactor, (PAFC), with n-hexadecane, C16H34, canola biodiesel, soybean biodiesel and petroleum diesel fuel has been investigated. Fifteen-hour steady-state operation was achieved with each of the diesel fuels. This is the first extensive study reported in the literature in which n-hexadecane is used directly as the fuel. It is also the first study of a fuel cell operated with petroleum diesel fuel. Identification of steady-state conditions (temperature = 190oC, molar ratio of fuel to water = 414) is significant because it demonstrates that stable fuel cell operation is technically feasible when operating a PAFC with diesel fuels. Degradation in fuel cell performance was observed prior to reaching steady-state. The degradation was attributed to a carbonaceous material forming on the surface of the anode. After treating the anode with water the fuel cell performance recovered. However, the fuel cell performance degraded again prior to obtaining another steady-state operation. Several consistent observations suggested that the carbonaceous material formed from the diesel fuels might be a reaction intermediate necessary for steady-state operation. Finally, the experiments indicated that water in the phosphoric acid electrolyte could be used as the water required for the anodic reaction. The water formed at the cathode could provide the replacement water for the electrolyte, thereby eliminating the need to provide a water feed system for the fuel cell.

No description available.

Magister Scientiae Dentium - MSc(Dent) / Restorative systems classified as polyacid modified composite resins, or compomers, have appeared on the market. An example of this is Dyract AP. Dyract AP must be used with the Prime & Bond NT bonding system. Prime & Bond NT can be applied without any form of prior etching, or it can be applied after application of Non Rinse Conditioner, or it can be applied after etching with 36% phosphoric acid. The purpose of the study was to determine the qualitative microleakage of Dyract AP and its bonding systems, as well as the influence of saliva contamination there of. Freshly extracted, non-carious, human premolars were randomly divided into 8 groups of 18 teeth each. Apiseetomies coated with Polivar varnish and restored with amalgam were performed on all teeth. Class V type cavities of 3 mm diameter and 1,5 mm depth were prepared on the CEJ junction on the buccal side of all teeth. Dyract AP restorations were placed using the bonding procedures indicated: Group 1: P&B NT (Prime & Bond NT); group 2: acid (36% phosphoric acid) + P&B NT; group 3: NRC (Non Rinse Conditioner) + P&B NT; group 4: P&B NT + Saliva; group 5: acid + Saliva + P&B NT; group 6: acid + P&B NT + Saliva; group 7: NRC + Saliva + P&B NT; group 8: NRC + P&B NT + Saliva. Restorations were finished with Sof-Lex discs. After 24 hours storage in distilled water the teeth were removed and coated with two layers of nail varnish, except for 1 mm around the restorations. The teeth were then thermocycled in a 0.5% basic fuchsin solution for 500 complete cycles between 8°C and 50°C, with a dwell time of 15 seconds.