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Solid phosphoric acid is a catalyst used for the upgrading of light olefins into fuels. To delve into the mechanism of olefin dimerisation over the catalyst, the oligomerisation of 1- hexene was investigated over a wide range of operating conditions. The reaction progression of 1-hexene dimerisation over solid phosphoric acid was interpreted by means of kinetic experiments for both a linear hexene (1-hexene) and a branched hexene (2,3-dimethylbutene). The reaction rate for both reagents was described by using an elementary kinetic model. From the experimental data it was shown that the rate of dimerisation of branched hexenes was faster than the rate observed for linear hexene dimerisation. To correlate the two sets of kinetic data, the reaction network was expanded to incorporate skeletal isomerisation of 1-hexene with dimerisation only taking place by the co-dimerisation of linear and branched hexenes and the dimerisation of branched hexenes. The fit of the kinetic equation demonstrated that the reaction rate of 1-hexene is essentially controlled by the rate of skeletal isomerisation. Due to the large activation energy for skeletal isomerisation, low reaction temperatures favoured the co-dimerisation of linear and branched hexenes whereas at higher temperatures, the reaction rate was dominated by the dimerisation of branched hexenes. The product distribution indicated that, because of the fast rates of both cracking and secondary dimerisation (dimerisation of cracked products), the product distribution instantaneously reached a pseudo equilibrium after the dimerisation of hexenes. Therefore the carbon distribution was found to depend only on the reaction temperature, not on the residence time in the reactor. Solid phosphoric acid is a supported liquid phosphoric acid where the condensed state of the acid, e.g. ortho phosphoric acid (H3PO4) and pyro phosphoric acid (H4P2O7), is dependent on the quantity of water present in the reaction mixture. With a decrease in water content, the distribution of acid shifts and the ortho phosphoric acid becomes more condensed (H4P2O7, H5P3O9 etc.), i.e. high water content → low acid strength, low water content → high acid strength. The experiments completed at various degrees of catalyst hydration and free acid loading showed that the rate of reaction over solid phosphoric acid was dependent on the acid strength of the catalyst. The effect of acid strength on the reaction rate was integrated into the rate constants by means of an exponential dependency on acid strength. It was also shown that both the product distribution and the degree of branching remained unaffected by acid strength. The constant product indicates that the rate of cracking is limited by the rate of oligomerisation of hexenes, irrespective of the acid strength of the catalyst. Since the product from the dimerisation of 1-hexene could be used as fuel, the quality of the desired fuel would therefore depend solely on the reaction temperature, not on the hydration of the catalyst. The work performed in this thesis has been published in two peer-review articles: 1. Schwarzer R.B., Du Toit E. and Nicol W. (2008) Kinetic model for the dimerisation of 1-hexene over a solid phosphoric acid catalyst, Applied Catalysis A: General, 340, 119-124. 2. Schwarzer R.B., Du Toit E. and Nicol W. (2009) Solid phosphoric acid catalysts: The effect of free acid composition on selectivity and activity for 1-hexene dimerisation, Applied Catalysis A: General, 369, 83-89. / Thesis (PhD(Eng))--University of Pretoria, 2012. / Chemical Engineering / unrestricted

M.S.

The alkylation of various compositions of propane with ethylene at atmospheric pressure in the presence of various concentrations of ortho-phosphoric acids and mixtures of ortho-phosphoric acid and hydrochloric and sulfuric acids as catalyst was investigated. Physical conditions studied were (1) temperature ranging from 40 to 200°C., (2) length of run from six to eight hours, and (5) vapor feed rate from 100 to 200 eubie centimeters per minute. From the results obtained from this research, it is evident that pipe still vapors composed of ethylene and propane cannot be alkylated at atmospheric pressure and relatively low temperatures with the use of 85-100 per cent ortho-phosphoric acid as a catalyst. No mechanism of reaction has been proven. / M.S.

From the results obtained in this investigation, the following conclusions can be drawn: 1. A substance inhibits corrosion only under certain conditions, and under other conditions it may not be an inhibitor, but may be inert or an accelerator. 2. No compounds tested in concentrations of 0.01 and 0.10 percent nitrogen, were found to inhibit the corrosion of steel in 5 percent phosphoric acid at 25°C. and under the conditions of aeration and agitation used. 3. Sodium chromate is an inhibitor in concentrations of 1 percent for the corrosion of steel by a 5 percent, aerated, agitated, phosphoric acid solution at 25°C. 4. The mechanism of the corrosion of copper proposed by Whaley is not substantiated. Chelation probably is not the mechanism by which 2-nitro-l-butanol inhibits the corrosion of copper in a 5 percent phosphoric acid solution. 5. Inhibitors that are used and are efficient for one acid under certain conditions cannot always be said to work for other acids under other conditions. / M.S.

Les minerais de phosphates, principalement exploités pour la production d'acide phosphorique et d'engrais, contiennent une quantité non-négligeable d'uranium (50 à 300 ppm) qui suscite l'intérêt de l'industrie nucléaire. Notre étude s'inscrit dans ce contexte de valorisation de l'uranium en tant que sous-produit de l'industrie des fertilisants.L'objectif de ce travail de thèse a été de mettre au point un matériau hybride, constitué d'un support inorganique sur lequel est greffée une molécule complexante, capable d'extraire sélectivement l'uranium du milieu acide phosphorique. La première étape de notre démarche a consisté à identifier un support inorganique capable de résister aux conditions particulières du milieu acide phosphorique (acidité élevée et milieu très complexant). Pour ce faire, la stabilité chimique et mécanique de différents matériaux, silice, verre et carbone mésoporeux, a été étudiée. Dans un deuxième temps, nous nous sommes intéressés à l'identification et l'optimisation de molécules complexantes spécifiques de l'uranium en milieu acide phosphorique. Ces dernières ont ensuite été greffées sur les supports les plus stables. Enfin, l'efficacité de ces systèmes hybrides a été évaluée lors de tests d'extraction, de sélectivité et de désextraction. / Phosphate rocks are industrially processed in large quantities to produce phosphoric acid and fertilisers. These rocks contain significant concentration of uranium (50 to 300 ppm) which could be interesting for nuclear industry. This work deals with the valorisation of uranium as a by-product from fertiliser industry.The aim of this study is to develop a hybrid material, constituted of an inorganic solid support grafted with an extractant (complexing molecule), which can extract selectively uranium from phosphoric acid medium. The first step of our approach was to identify an inorganic support which is stable under these particular conditions (strong acidity and complexing medium). The chemical and mechanical stability of different mesoporous materials, such as silica, glass and carbon was studied. In a second phase, we focused on the identification and the optimisation of complexing molecules, specific of uranium in phosphoric acid. These ligands were then grafted on the most stable solids. Finally, the efficiency of these hybrid systems was evaluated through different tests of extraction, selectivity and desextraction.

The synthesis of enantiomerically pure compounds is of vital importance. Most biologically active natural products are chiral and require asymmetric synthesis, chiral resolution, or the use of naturally chiral starting materials for their preparation. Organocatalytic enantioselective reaction methodology is a continuously growing area in organic chemistry. The use of organocatalysts as a potentially environmentally friendly alternative to metal catalysts is appealing to the pharmaceutical industry. In this dissertation an enantioselective Mannich reaction using an organocatalyst was investigated. The reaction was between a ß-keto ester and an imine electrophile catalyzed by vaulted biphenanthrol (VAPOL) phosphoric acid. The reaction resulted in products with high yields, but low to moderate enantioselectivity and diastereoselectivity. The development of the first Brønsted acid-catalyzed desymmetrization of meso-aziridines was also investigated. This is one of the first instances where a phosphoric acid has been used to catalyze a reaction that did not involve an imine. It was shown that the chiral VAPOL phosphoric acid was an excellent catalyst for the reaction resulting in high yields and enantioselectivities for the chiral ring opened products. It was also shown, for the first time, that a vaulted binaphthol (VANOL) phosphoric acid can also catalyze the ring-opening of meso-aziridines with comparable results to the VAPOL phosphoric acid in some cases. Mechanistic NMR studies were used to probe the reaction, and it is believed that evidence leads one to conclude that a unique mechanism for phosphoric acid-catalysis is followed. The products that can be obtained from this reaction, 1,2-diamines, are of high value for synthetic chemists. They have been used as chiral auxiliaries, ligands, and precursors to natural products.

Succinic acid is a compound used for manufacturing lacquers, resins, and other coating chemicals. It is also used in the food and beverage industry as a flavor additive. It is predominantly manufactured from petrochemicals, but it can also be produced more sustainably by fermentation of sugars from renewable feedstocks (biomass). Bio-based succinic acid has excellent potential for becoming a platform chemical (building block) for commodity and high-value chemicals. In this study, we focused on the production of bio-based succinic acid from the fiber of sweet sorghum (SS), which has a high fermentable sugar content and can be cultivated in a variety of climates and locations around the world. To avoid competition with food feedstocks, we targeted the non-edible ‘bagasse’, which is the fiber part after extracting the juice. Initially, we studied various conditions of pretreating SS bagasse to remove most of the non-fermentable portions and expose the cellulose fibers containing the fermentable sugars (glucose). Concentrated (83%) phosphoric acid was utilized at mild temperatures of 50-80 °C for 30-60 minutes at various bagasse loadings (10-15%) using a partial factorial experimental design. After pretreatment, the biomass was subjected to enzymatic hydrolysis with commercial cellulase enzyme (Cellic® Ctec2) to identify the pretreatment conditions that lead to the highest glucose yield that is critical for the production of succinic acid via fermentation with the bacterium Actinobacillus succinogenes. As the pretreatment temperature and duration increased, the bagasse color changed from light brown to dark brown-black, indicating decomposition, which ranged from 15% to 72%. The pretreatment results were fitted with an empirical model that identified 50 °C for 43 min at 13% solids loading as optimal pretreatment conditions that lead to the highest glucose release from sweet sorghum bagasse. Biomass pretreated at those conditions and subjected to separate enzymatic hydrolysis and fermentation with A. succinogenes yielded almost 18 g/L succinic acid, which represented 90% of the theoretical yield, a very promising performance that warranties further investigation of bio-based succinic acid production from sweet sorghum bagasse, as a more sustainable alternative to succinic acid produced from fossil sources, such as oil.

The development of novel asymmetric reaction methodologies has been invaluable in both the academic and industrial world. In just 15 years, organocatalysis has provided a new means of developing asymmetric reaction methodologies using catalysts that are environmentally benign, relatively inexpensive, bench stable, and non-toxic. One development in organocatalysis that is important to our group in particular is chiral phosphoric acid-catalysis. BINOL-derived and VAPOL-derived phosphoric acids have proven to be excellent catalysts for a number of reactions. The two projects I will discuss my efforts on are acetalization and iso-Pictet-Spengler reactions. These were projects that I performed during my first two years as a graduate student. The acetalization was particularly fascinating as only one literature report existed for the catalytic asymmetric variant of a reaction that makes such important compounds--O,O-acetals. The acetalization reaction proved to be a formidable opponent, and to this date no research report has been published documenting the intra-, or intermolecular catalytic asymmetric acetalization of vinyl ethers or the intermolecular catalytic asymmetric transacetalization. The iso-Pictet-Spengler reaction is one that is interesting because exhaustive research has been conducted into the development of catalytic asymmetric Pictet-Spengler reactions, but at the time of my research, not a single catalytic asymmetric method existed to synthesize tetrahydro-γ-carbolines, the product of the iso-Pictet-Spengler reaction. Structurally, the tetrahydro-γ-carboline is isomeric to the tetrahydro-β-carboline, the product of the Pictet-Spengler reaction. They differ only in the position of nitrogen in the annulated product. This reaction seemed attractive to investigate, since independent elegant reports by Professors Benjamin List, Henk Hiemstra, and Darren Dixon documented the excellent control over enantioselectivity that chiral phosphoric acid have in the Pictet-Spengler reaction. Concurrent with the beginning stages of this project, Professor Eric Jacobsen reported the enantioselective thiourea-catalyzed iso-Pictet-Spengler reaction. The results were very good but not as great as the Pictet-Spengler work he pioneered. Around the time this report came out I commenced my reaction studies, and this thesis is the sum of just two projects I worked on. There were many more including halolactonization, VAPOL synthesis, chiral phosphoric acid synthesis, catalytic asymmetric hydroamination, and others.