The thiopyran route to polypropionates is an attractive strategy that involves a stepwise iterative aldol homologation of tetrahydro-4H-thiopyran-4-one (I) with thiopyran aldehyde (II) followed by desulfurization to rapidly assemble stereochemically complex polypropionate synthons. <p>In chapter 1, the thesis is summarized in the context of relevant background research including; a) the basic principle of the thiopyran route; b) dynamic kinetic resolution of -substituted aldehydes; c) previous syntheses of serricornin; iv) previous syntheses of membrenones.<p>In chapter 2, proline-catalyzed enantioselective direct intermolecular aldol reactions of tetrahydro-4H-thiopyran-4-one with various achiral aldehydes were studied. The results provided insights on the behaviour and stereoselectivity profile of thiopyranone (a crucial starting block in the thiopyran design) in the proline-catalyzed aldol reaction.<p>In chapter 3, inspired by the results of the aldol reaction of ketone (I) with achiral aldehydes, we next investigated the proline-catalyzed asymmetric aldol reactions of (I) with racemic thiopyran aldehyde (II) as a strategy to rapidly prepare enantiomerically pure tetrapropionate synthons without any requirement of enantioenriched aldehyde. The reaction occurred with high enantiotopic group selectivity and dynamic kinetic resolution.<p>In chapter 4, a detailed study to ascertain the scope and limitations of the design strategy described in chapter 3 was extended towards other catalysts, aldehydes and ketones. <p>Finally, applications of the above mentioned strategy towards the synthesis of serricornin and membrenones A and B are elaborated in chapters 5 and 6 respectively.

The thiopyran route to polypropionates is an attractive strategy that involves a stepwise iterative aldol homologation of tetrahydro-4H-thiopyran-4-one (I) with thiopyran aldehyde (II) followed by desulfurization to rapidly assemble stereochemically complex polypropionate synthons. <p>In chapter 1, the thesis is summarized in the context of relevant background research including; a) the basic principle of the thiopyran route; b) dynamic kinetic resolution of -substituted aldehydes; c) previous syntheses of serricornin; iv) previous syntheses of membrenones.<p>In chapter 2, proline-catalyzed enantioselective direct intermolecular aldol reactions of tetrahydro-4H-thiopyran-4-one with various achiral aldehydes were studied. The results provided insights on the behaviour and stereoselectivity profile of thiopyranone (a crucial starting block in the thiopyran design) in the proline-catalyzed aldol reaction.<p>In chapter 3, inspired by the results of the aldol reaction of ketone (I) with achiral aldehydes, we next investigated the proline-catalyzed asymmetric aldol reactions of (I) with racemic thiopyran aldehyde (II) as a strategy to rapidly prepare enantiomerically pure tetrapropionate synthons without any requirement of enantioenriched aldehyde. The reaction occurred with high enantiotopic group selectivity and dynamic kinetic resolution.<p>In chapter 4, a detailed study to ascertain the scope and limitations of the design strategy described in chapter 3 was extended towards other catalysts, aldehydes and ketones. <p>Finally, applications of the above mentioned strategy towards the synthesis of serricornin and membrenones A and B are elaborated in chapters 5 and 6 respectively.

No description available.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The content of sulfur compounds in asphalt is related to parameters of quality as reactivity, corrosiveness, toxicity and potential polluter, among others. In this work, a method for simultaneous determination of inorganic and organic low molecular weight sulfur compounds was developed. The analytes were stripped from asphaltic samples by gaseous diffusion. For the simultaneous determination of inorganic (20 to 100 μg L-1) and organics (80 to 400 μg L-1) sulfides, Cathodic Stripping Voltammetric (CSV) was used, with the mercury electrode operating at the HMDE mode in hydrazine 0.05 mol L-1 pH 2.3 solution as support electrolyte. The same conditions were used to speciate methanethiol (25 to 125 μg L-1) and propanethiol (30 to 150 μg L-1) through curve derivation. The calculated quantification limits were 0.22 μg L-1 for inorganic sulfide, 0.30 μg L-1 for organic sulfides; 1.08 μg L-1 for methanethiol and 0.16 μg L-1 for propanethiol. For studies concerning gaseous diffusion in asphaltic matrices, H2SO4 1.5 mol L-1 (ionic strength 4.5 mol L-1) was used as donor solution and NaOH 0,1 mol L -1 as the acceptor one. Diffusion intervals of 20 and 30 minutes under stirring were used to separate the analytes from the matrices. For crude asphalt samples, recoveries of 49% for organic sulfides and 100% for inorganic sulfide were obtained and, 40% for organic sulfides and 83% for inorganic sulfide were obtained for asphalt fraction samples. / O teor de compostos de enxofre em asfalto tem relação com parâmetros de qualidade como reatividade, corrosibilidade, toxicidade e potencial poluidor. Neste trabalho, um método para a determinação simultânea de compostos de enxofre inorgânico e orgânicos de baixo peso molecular foi desenvolvido. A separação dos analitos das amostras asfálticas foi realizada por difusão gasosa. Para a determinação simultânea de sulfetos inorgânico (20 a 100 Qg L−1) e orgânicos (80 a 400 Qg L−1), utilizou-se a voltametria de redissolução catódica, com eletrodo de mercúrio no modo HMDE, em hidrazina 0,05 mol L−1 pH 2,3. As mesmas condições foram utilizadas para a especiação de metanotiol (25 a 125 Qg L−1) e propanotiol (30 a 150 Qg L−1) através da derivação dos sinais. Os limites de quantificação calculados foram de 0,22 Qg L−1 para sulfeto inorgânico, 0,30 Qg L−1 para sulfetos orgânicos, 1,08 Qg L−1 para metanotiol e 0,16 Qg L−1 para propanotiol. Nos estudos envolvendo a difusão gasosa em matrizes asfálticas utilizou-se H2SO4 1,5 mol L−1 (força iônica 4,5 mol L−1) como solução doadora e NaOH 0,1 mol L−1 como solução receptora. Intervalos de difusão de 20 e 30 minutos sob agitação mecânica foram utilizados para separação dos analitos das matrizes. Para asfalto bruto, recuperações de 49% para sulfetos orgânicos e 100% para sulfeto inorgânico foram obtidos e, para asfalto fracionado recuperações de 40% para sulfetos orgânicos e 83% para sulfeto inorgânico.

No description available.

S-adenosyl-L-homocysteine (AdoHcy) hydrolase effects hydrolytic cleavage of AdoHcy to produce both adenosine and L-homocysteine and is a feedback inhibitor of S-adenosyl-L-methionine (SAM). Nucleoside analogues bearing an alkenyl or fluoroalkenyl chain between sulfur and C5′ utilizing Negishi coupling reactions were synthesized. Palladium-catalyzed cross-coupling between the 5′-deoxy-5′-(iodomethylene) nucleosides and alkylzinc bromides gives analogues with the alkenyl unit. Palladium-catalyzed selective monoalkylation of 5′-(bromofluoromethylene)-5′-deoxy-adenosine with alkylzinc bromide afford adenosylhomocysteine analogues with a 6′-(fluoro)vinyl motif. The vinylic adenine nucleosides produced time-dependent inactivation of the S-adenosyl-L-homocysteine hydrolases. Stannydesulfonylation reaction is a critical step in the synthesis of E-fluorovinyl cytidine (Tezacitabine) a ribonucleoside reductase inhibitor with a potent anticancer activity. The synthesis involves the removal of the sulfonyl group by a radical-mediated stannyldesulfonylation reaction using tributyltin hydride. In order to eliminate the toxicity of tin, I developed a radical-mediated germyldesulonylation utilizing less toxic germane hydrides. Treatment of the protected (E)-5'-deoxy-5'-[(p-toluenesulfonyl)-methylene]uridine and adenosine derivatives with tributyl- or triphenylgermane hydride effected radical-mediated germyldesulfonylations to give 5'-(tributyl- or triphenylgermyl)methylene-5'-deoxynucleoside derivatives as single (E)-isomers. Analogous treatment of 2'-deoxy-2'-[(phenylsulfonyl)methylene]uridine with Ph3GeH afforded the corresponding vinyl triphenylgermane product. Stereoselective halodegermylation of the (E)-5'-(tributylgermyl)-methylene-5'-deoxy nucleosides with NIS or NBS provided the Wittig-type (E)-5'-deoxy-5'-(halomethylene) nucleosides quantitatively. Radical-mediated thiodesulfonylation of the readily available vinyl and (α-fluoro) vinyl sulfones with aryl thiols in organic or aqueous medium to provide a bench and environmentally friendly protocol to access (α-fluoro)vinyl sulfides were developed. Methylation of the vinyl or (α-fluoro)vinyl phenyl sulfide gave access to the corresponding vinyl or (α-fluoro)vinyl sulfonium salts. These sulfonium ions were tested as possible methyl group donors during reactions with thiols, phenols or amino groups which are commonly present in natural amino acids.

A probe for measuring the specific heat of superconductors at low temperatures and in high magnetic fields has been built and commissioned. The probe has been tested using the relaxation method on samples of copper and the accuracy of the data is 1.3 % between 5 K and 30 K, data taken using the long range pulse method has a resolution of 10 mK. Specific heat measurements have been performed on members of the series (Pb(_1)-(_x))Cu(_1.8x)Mo(_6)S(_8), (Sn(_1-x))Eu(_x)Mo(_6)S(_8) and (Pb(_1-x)M(_x))Mo(_6)S(_8) where M = Gd and Eu, from 3 K up to 30 K and in magnetic fields up to 15 T. Additional results from resistivity, susceptibility, magnetisation. X-ray diffraction, transmission electron microscopy and electron dispersive-ray measurements are also presented. These data have been compared to results from other authors and are analysed in terms of the BCS and GLAG theories of superconductivity and the magnetic properties of these materials. The mean field model has been used to calculate numerically the magnetic contribution to the specific heat (cm) of both ferromagnetic and antiferromagnetic systems as a function of temperature and applied field both above and below the ordering temperature. In addition an approximate analytic form for the magnetisation has been used to calculate Cm above the ordering temperature. Expressions have been derived for the saturation value of the peak in C(_m): C(^sat)(_m) = 1.1245n(_cell)RJI(J+1) and the temperature dependence of the peak with applied field ȡ(μ(_o)H(_ext))/ȡT(_peak)=6.540/g(_J)(J+1). They allow the simple calculation of the values of J and g(_J)(J + 1) from specific heat data. The magnetic contribution to the specific heat of the samples (Sn(_0.65)Eu(0.35)Mo(_6)S(_8)) and (Sn(0.50)Eu(_0.50)Mo(_6)S(_8)) have been modelled using these calculations and excellent agreement is found by considering the magnetic ions as free ions. The sample is accurately modelled by including an additional minority phase (Gd(_2)S(_3)). The approximate expressions have also been used to analyse data on high temperature superconductors producing values of J and g(_J)}{J + 1) consistent with a doublet ground state. The properties of Chevrel phase materials have been determined as a function of doping level. The critical temperature is degraded by doping but an increase in the critical current density is observed in the series (Pb(_1-x)Cu(_1-8x)Mo(_6)S(_8) for very low levels of doping. Increases of up to 28 % in the upper critical field, that are probably due to the compensation effect and an increase in the normal state resistivity, are also observed in the series (Sn(_1-x)Eu(_x)Mo(_6)S(_8)) at high levels of doping and in the series (Pb(_1-x)Gd(_x)Mo(_6)s(_8) for low levels of doping.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2014-09-18T15:26:45Z No. of bitstreams: 2 Dissertação Danilo G Batista 2013_ Final.pdf: 14272139 bytes, checksum: 1046108060b4c8d18c18e82aa11daf9d (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2014-09-18T15:41:57Z (GMT) No. of bitstreams: 2 Dissertação Danilo G Batista 2013_ Final.pdf: 14272139 bytes, checksum: 1046108060b4c8d18c18e82aa11daf9d (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2014-09-18T15:41:57Z (GMT). No. of bitstreams: 2 Dissertação Danilo G Batista 2013_ Final.pdf: 14272139 bytes, checksum: 1046108060b4c8d18c18e82aa11daf9d (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2013-10-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / A long time ago aggregate particles were considered inert but this concept is no longer adequate. Expansive reactions resulting from the oxidation of sulfide-bearing aggregates and the AAR are examples of potential chemical interactions that aggregates may experience in concrete, depending on the surrounding environment. This research is an investigation into concrete deterioration in Hydroelectric Power Plants (HPPs), focusing on aggregate reactions relating to attack by sulfates, due to oxidation of sulfide minerals, as well as to the alkali-aggregate reaction (AAR). One of the main purposes is to have a clearer understanding of the changes in sulfide minerals occurring in aggregates and verify their influence on concrete durability as well as check the conditions and characteristics that maximize or not the synergy of such pathology. Along with that, another purpose is to study the possibility of the AAR occurring in the same structures. To this end, an investigation of concrete structures extracted from five Brazilian hydroelectric plants, namely Corumbá HPP, Marechal Mascarenhas de Moraes HPP, Paulo Afonso II HPP, Paulo Afonso IV HPP and Moxotó HPP, was conducted. In addition to the concretes, a study of the rocky material and aggregates surrounding the plants that were of the same origin as the aggregates in the concretes was also performed. A thorough visual inspection was made in the field of some concrete structures selected from the HPPs , with the subsequent extraction of concrete cores in spots that were more prone to the incidence of some chemical reaction. The concrete core samples were initially inspected in the laboratory to check for possible visible anomalies on their surfaces, and were subsequently subjected to laboratory tests to determine the mechanical properties such as compressive strength and elasticity modulus. Chemical and microstructural analyses of the concrete were then carried out, in addition to the reconstitution of the mix design and determination of their pH. The concrete were also underwent internal inspections before the microstructural analyses, and the last were scanning electron microscopy with energy-dispersive X-ray spectrometry (EDS) and X-ray diffraction (XRD) in order to diagnose deterioration. Aggregates extracted from concrete cores along with the rocky material of the same origin were also subjected to chemical and mineralogical analyses. The concrete from Corumbá HPP was found to be sound, but in the concretes from the other HPPs it was proved the incidence of AAR and sulfate attack simultaneously, and in some cases, with evidences that the attack by sulfates results from the oxidation of sulfide minerals in the aggregates. / Durante muito tempo as partículas de agregados foram consideradas inertes; entretanto, atualmente esse conceito foi banido. Reações expansivas decorrente da oxidação de minerais sulfetos presentes em agregados e da reação álcali-agregado (RAA) são exemplos de interações químicas potenciais que os agregados podem experimentar quando presentes no concreto, dependendo do meio circundante. A presente pesquisa aborda a investigação de concretos de UHEs com foco na deterioração por reações com os agregados no que tange ao ataque por sulfatos, devido à oxidação de minerais sulfetos, bem como à RAA. Objetiva-se avançar no entendimento do fenômeno de alteração de minerais sulfetos presentes em agregados e verificar a sua influência sobre a durabilidade de concretos, além de verificar as condições e características que maximizam ou não a sinergia desta patologia. Conjuntamente, pretende-se também estudar, nas mesmas estruturas, a possibilidade de ocorrência da RAA. Para tanto, procedeu-se com uma investigação de concretos extraídos de estruturas pertencentes a cinco usinas hidrelétricas brasileiras, a saber: UHE Corumbá, UHE Marechal Mascarenhas de Moraes, UHE Paulo Afonso II, UHE Paulo Afonso IV e UHE Moxotó. Além dos concretos, procedeu-se também com um estudo do material rochoso e dos agregados do entorno das usinas, de mesma origem que os agregados dos concretos. Inicialmente foi realizada criteriosa inspeção visual em campo de algumas estruturas de concreto selecionadas das UHEs, com posterior extração de testemunhos em locais com maior propensão da incidência de alguma reação química. Os testemunhos de concreto foram inicialmente inspecionados em laboratório para a verificação de possíveis anomalias visíveis em suas superfícies, sendo posteriormente submetidos a ensaios laboratoriais para a determinação das propriedades mecânicas de resistência à compressão e módulo de elasticidade. Foram, na sequência, realizadas análises químicas e microestruturais dos concretos, além da reconstituição de traço e obtenção do pH. Os concretos também foram submetidos a inspeções internas antes das análises microestruturais, sendo estas últimas a microscopia eletrônica de varredura com espectrometria por energia dispersiva de raios X (EDS) e a difração de raios X (DRX), ambas com o objetivo de diagnosticar deterioração. Os agregados extraídos dos concretos juntamente com o material rochoso de mesma origem também foram submetidos a análises químicas e mineralógicas. Pelos resultados, verificou-se boa integridade dos concretos da UHE Corumbá, porém para as demais usinas, constatou-se nos concretos a incidência de RAA, além de ataque por sulfatos, tendo alguns dos concretos das demais usinas indícios de que o ataque por sulfatos é decorrente da oxidação de minerais sulfetos presentes nos agregados.

Thesis (Master of Engineering in Chemical Engineering)--Cape Peninsula University of Technology, 2018. / Acid rock drainage (ARD) is one of the most severe environmental challenges currently faced by the mining industry worldwide. ARD is formed from the oxidation of sulphide-bearing minerals, particularly pyrite, in the presence of water and oxygen. ARD generation is accelerated by the presence of naturally occurring iron and sulphur-oxidizing micro-organisms, which regenerate leaching agents that facilitate sulphide mineral oxidation. ARD pollution is characterized by a high concentration of metals and sulphates in solution, low pH and a high salt content (salinity) in the environment, contaminating soil and groundwater. In South Africa, ARD is a major challenge in the gold and coal mining industries, where millions of tons of sulphide waste rock and overburden are generated and discarded. Characterization of these waste materials is required to develop an appropriate disposal strategy to minimise the risk of pollution and the generation of ARD. Potential ARD generation prediction from waste rock depends on the precise characterization of ARD potential using Biokinetic tests. Commonly used ARD prediction methods are static and long-term kinetic tests. Static tests provide data for a worst-case scenario focussing on strong acid chemical leaching potential to give an overall acid forming potential of a sample. Such kinetic tests provide data illustrating the rate of the net acid generation capacity of mine waste. However, these tests are capital intensive and time-consuming and fail to provide adequate information on the effect of micro-organisms on the overall net acid generation capacity of mine waste. The Biokinetic test reported herein and developed at the University of Cape Town, focusses on addressing a worst case scenario provided by static tests in a cost-effective manner and reduced time frames provided for by conventional kinetic tests. This test primarily provides relative rates of ARD generation in the presence of micro-organisms within 90 days. However, the Biokinetic test is at the developmental stage and thus far, has not been consistently used for different waste ores to determine a standardised approach. Therefore, the aim of this study was to investigate the effects of microbial consortia and to develop a standardisation approach for the test for ARD formation potential using gold-bearing and copper-bearing waste rock. Additionally, to refine the Semi-continuous Biokinetic test simulation, a flow-through system where there is minimal seepage in the waste deposit, was also developed. The sulphur content of the gold and copper-bearing samples used in this study was between 2.3 and 3.15%, respectively. These waste rock samples were found to be potentially acid- forming. In the Biokinetic test, finely milled waste rock samples were slurrified, inoculated with consortia and cultured under standard bioleaching conditions. Leaching and acidification rates were monitored.

Macrocyclic ligand-complexed transition metal-oxo intermediates are the active oxidizing species in a variety of important biological and catalytic oxidation reactions. Many transition metal catalysts have been designed to mimic the predominant oxidation catalysts in nature, namely the cytochrome P450 enzymes. Iron porphyrin complexes have been the center of research as catalysts. In this study 5,10,15,20- tetramesitylporphyrin (H2TMP) and its corresponding iron complexes FeIII(X)TMP (X= Cl, ClO4, ClO3, NO3, NO2, and BrO3) have been successfully synthesized and fully characterized by UV-vis and NMR spectroscopies. For the catalytic selective oxidation of organic sulfides, the potential of iron(III) porphyrin complexes with iodobenzene diacetate [PhI(OAc)2] have been investigated. Iodobenzene diacetate was found to be an efficient oxygen source in the iron(III) porphyrin-catalyzed oxidation of sulfides to sulfoxides. Iron(III) porphyrin catalysts show an excellent conversion and selectivity for the sulfoxidation reactions. Reaction conditions and environments that effect the catalytic sulfoxidation including solvent, catalytic amount, axial ligand, water, and thioanisole substrates, have been investigated to identify the optimal conditions and the substrate scope. Under optimized conditions, excellent substrate conversions (up to 100%) as well as product selectivies (sulfoxide:sulfone > 95:5) have been achieved. To probe the nature of the oxidizing species in above catalytic sulfoxidations, iron(IV)-oxo porphyrin radical cations model of Compound I were chemically produced from the corresponding iron(III) tetramesitylporphyrin precursors with excess amounts of PhI(OAc)2 (20-50 equivalents) in CH3CN solvent. All O=FeIV(X)TMP·+ (X= Cl, ClO4, ClO3, and NO3) show weaker Soret band and broader Q band that are characteristic of Compound I analogues. A new photochemical method that led to generation of the iron(IV)-oxo porphyrin radical cations was also successfully developed. Iron(IV)-oxo porphyrin radical cations were generated by irradiation of iron(III) porphyrin chlorate or bromate complexes that result in heterolytic cleavage of the O-X bond in the axial ligand.