It is generally recognized that the recovery of particles from a flotation pulp is controlled by (i) the flotation rate constant and (ii) the residence time distribution of the particles. In the present work, theoretical and experimental analyses have been carried out to develop methods for predicting these parameters from first principles considerations. In order to predict the flotation rate constant, a bubble-particle interaction model has been developed using a dynamic force balance to determine the trajectory of a particle as it approaches a rising air bubble. The trajectory has been used to determine the probability of bubble-particle attachment, from which the flotation rate constant can be readily obtained. The model is unique in that it simultaneously considers the effects of hydrodynamic and surface forces on the interaction between bubbles and particles. Model predictions have been shown to be in good agreement with results from bubble-particle attachment experiments for narrowly-sized coal and silica samples. In the present work, the residence time distribution of particles in column flotation has been examined by conducting experimental tracer tests. These tests have been performed with two tracer materials to characterize mixing for both the liquid and the solids in a single system. The measured residence time distributions have shown that the assumption of equating liquid and solids residence time distributions is inappropriate, except for very small and low density particles. At larger sizes and higher densities, the correction formula advocated by Dobby and Finch (1985) has been shown to adequately predict the solids residence time. / Master of Science

The interactions of O-isopropyl-N-ethylthionocarbamate (IPETC) and O-isobutyl-N-ethoxycarbonylthionocarbamate (IBECTC) with Cu₂S, CuFeS₂ and FeS₂ have been characterized using thermodynamic calculations, electrochemistry, microflotation tests, contact angle measurements, FTIR, and UV spectroscopy. Pearson’s theory of hard and soft acids and bases (HSAB) has also been applied to these flotation systems, through the use of Drago’s acid-base concept and flow microcalorimetry. The results of the thermodynamic calculations and electrochemical measurements suggest that IPETC and IBECTC adsorption on copper and chalcocite are dependent on potential. This has been verified by contact angle and in-situ spectroelectrochemical measurements. Microflotation tests with these thionocarbamates show that the floatability of Cu₂S and CuFeS₂ is dependent on pH. The floatability of FeS₂ only becomes significant at acidic conditions and high collector additions. Spectroscopic measurements also show that thionocarbamate adsorption is dependent on pH and is most favored on Cu₂S followed by CuFeS₂ and FeS₂. FTIR results indicate that IPETC is adsorbed on Cu°, Cu₂S, and CuFeS₂ through a coordination of the sulfur atom with the surface Cu. IBECTC adsorption on these substrates involves the coordination of Cu with both sulfur and oxygen atoms to form a six-membered chelate ring. Adsorption of these collectors cannot remove or prevent the formation of sulfoxy oxidation products on the FeS₂ surface, unlike the case with the xanthate-pyrite system. This may explain the improved selectivity of IPETC and IBECTC over xanthates. Infrared reflection-absorption spectroscopic studies show that KEX is preferentially adsorbed on Cu° over IPETC and IBECTC. Between IPETC and IBECTC, the latter is more favorably adsorbed than the former. Kinetic studies using UV spectroscopy show that the rate of thionocarbamate adsorption is highest on Cu₂S followed by CuFeS₂ and FeS₂. IBECTC adsorption on each sulfide mineral is relatively faster than IPETC, indicating the higher collecting power of IBECTC. The HSAB concept suggests that the interaction of thionocarbamates (soft bases) with sulfide minerals that are classified as soft acids should be favored. The C/E ratios of Cu₂S and FeS₂ were determined to be 0.86 and 0.52, respectively. This indicates that FeS₂ is a harder acid than Cu₂S, thus providing an explanation for the observed selectivity of both IPETC and IBECTC against FeS₂. / Ph. D.

Thesis advisor: Amir H. Hoveyda / Chapter One: An overview of Cu-catalyzed enantioselective allylic substitutions with organometallic reagents. Chapter Two: Development of Cu-catalyzed enantioselective allylic alkylations of allylic chlorides with Grignard reagents for the formation of all-carbon quaternary stereogenic centers is disclosed. Chapter Three: Development of Cu-catalyzed enantioselective allylic substitutions of allylic phosphates with alkyl, aryl, and heterocyclic aluminum reagents for the formation of quaternary stereogenic centers is discussed. / Thesis (MS) — Boston College, 2010. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

This thesis includes NMR studies of free base meso-tetra(otolyl) porphyrin (TTP) and meso -tetraphenylporphyrin (TPP) and their dications protonated by trifluoroacetic acid (TFA). The chemical shift changes of the -NH resonance are very unusual and have never been reported. At the beginning of the titration, the N-H resonances broaden considerably but do not shift; when the ratio of [TFA]/[TTP] or [TFA]/[TPPf are over 2, the N-H resonances shift markedly to lower field by as much as 1.6 ppm. At acid levels well above the equivalence point, the NH resonances moves back to higher field. Moreover upon protonation the NH line of TTP becomes a complex multiplet which changes as a function of [TFA]/[TTP]. The NH line of TPP remains a singlet at all acid levels. We also report here a way of isolating atropisomers of mesotetra( o -tolyl)porphyrin through HPLC by using an analytical C-18 bond pack reverse phase column eluted by a 1 %THF + 99%Me0H solvent combination. A preliminary study by HPLC was also carried out on ZnTTP(II) with aliquots of 2,6-dimethylpyridine, and the retention time of the separation decreased markedly, but this study needs to be repeated and improved. TTP and TPP dications at two different acid levels were studied by VT-NMR, and the downfield shift of -NH resonance of TTP dications was more pronounced at higher temperatures than those of TPP dications.

I. Rhodium-Catalysed Carbometalation of Ynamides using Organoboron Reagents. As an expansion of existing procedures for the carbometalation of ynamides, it was discovered that [Rh(cod)(MeCN)2]BF4 successfully promotes the carbometalation of ynamides with organoboron reagents. A variety of organoboron reagents were found to be suitable for this reaction, but mostly the use of arylboronic acids was explored. The developed methodology provides β,β-disubstituted enamide products in a regio- and stereocontrolled manner. II. Palladium-Catalysed Hydroacyloxylation of Ynamides. In the presence of palladium(II) acetate, ynamides successfully underwent a hydroacyloxylation reaction with a variety of carboxylic acids. This carboxylic acid addition occurred highly regio- and stereoselectively to provide α-acyloxyenamides. Applications of the α-acyloxyenamide products were also investigated. III. Rhodium-Catalysed [2+2] Cycloaddition of Ynamides with Nitroalkenes. A novel rhodium catalyst system has been developed in order to promote the [2+2] cycloaddition reaction between ynamides and nitroalkenes. The reaction provides cyclobutenamide products and was diastereoselective in favour of the trans cyclobutenamide. Both the ynamide scope and the nitroalkene scope of the reaction have been explored.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Master / Master of Philosophy

The cobalt-catalysed alkylative aldol cyclisations of α,β-unsaturated amides with an appendant ketone were studied using a range of trialkylaluminium reagents. Investigations revealed that Co(acac)2·2H2O acts as an effective precatalyst for this transformation and the reaction provides β-hydroxylactam products containing three contiguous stereocentres with high levels of diastereoselection. The substrate scope of the reaction was explored and attempts were made to develop an asymmetric variant of this process. Two plausible reaction mechanisms have been proposed; the first invokes a π-allylcobalt species as a key intermediate in the reaction mechanism and the second involves a radical-mediated pathway. A stereochemical rationale for the observed relative stereochemistry of the β-hydroxylactam products has been discussed. II. Rhodium-Catalysed Carbometallations of Ynamides in the Preparation of Multisubstituted Enamides A highly stereo- and regioselective rhodium-catalysed carbozincation of ynamides using organozinc reagents has been disclosed. A careful examination of ligand effects on the rhodium catalyst yielded a complementary set of hydrozincation conditions. The alkenylzinc intermediates produced during the course of these reactions have been harnessed in further transformations with electrophilic species and in cross-couplings, thus providing access to multisubstituted enamides in a stereo- and regioselective fashion. Additionally, a rhodium-catalysed tandem carbometallation−conjugate addition with ortho-boronate substituted cinnamic acid derivatives has been described. The enamide−indene products were obtained in good yields and regioselectivities. Preliminary work has been undertaken on an asymmetric variant of this transformation and the initial results have been reported.

Thesis advisor: Amir H. Hoveyda / General and efficient methods for catalytic enantioselective synthesis of tertiary alcohols prepared by the addition of C-Metal nucleophiles to ketones. / Thesis (MS) — Boston College, 2008. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

A resistência de cinco microrganismos presentes na microbiota da área de produção estéril (Cristalização Estéril), frente a ação do gás de peróxido de hidrogênio foi determinada e o valor O obtido para cada microrganismo foi comparado ao valor D do Bacillus stearothermophilus ATCC 12980 exposto ao mesmo agente. Os microrganismos testados foram Bacillus sp, M. luteus, Corynebacterium, Staphylococcus sp e Penicillium sp. Este teste tinha a finalidade de comprovar que a resistência do Bacillus stearothermophilus é maior quando da exposição ao peróxido de hidrogênio se comparada a outros microrganismos presentes na área produtiva. A metodologia consistiu da inoculação de 0,01 mL da suspensão de cada microrganismo na contagem de 102UFC/0,01 mL em cupons de aço inoxidável, previamente esterilizados por calor seco e posterior exposição ao gás de peróxido de hidrogênio. O experimento demonstrou que o valor D obtido para o Bacillus stearothermophilus ésuperior aos obtidos para os outros microrganismos em teste comprovando que a escolha deste microrganismo para o desafio contra o peróxido de hidrogênio é apropriada. Também executou-se o teste que visava garantir que o aço inoxidável é o material de suporte mais recomendado para este fim, utilizando-se suportes de diversos materiais normalmente encontrados no interior dos isoladores (PVC, aço inoxidável, CKC, teflon, polipropileno, látex, silicone, Hypalon, vidro, nylon, saco de alumínio) com 0,01 mL de inóculo de Bacillus stearothermophilus na contagem de 102UFC/O,01 mL, o que foi devidamente comprovado. / The resistance of tive microrganisms found in the sterile production area (Crystallization Area) flora was tested against the hydrogen peroxide gas and the D value of each microrganism was compared to the Bacillus stearothermophilus D Value ATCC 12980 exposed to the same agent. The microrganisms tested were Bacillus sp, M. luteus, Corynebacterium, Staphylococcus sp e Penicillium sp. The purpose of this test was to prove that the resistance of Bacillus stearothermophilus against the exposition the hydrogen peroxide is higher when compared to others microrganisms found in the production area. The methodology consisted in inoculating 0.01 mL of microrganisms suspension with 102UFC/0,01 mL count in stainless steel coupons, treated previously with dry heat and further exposition to the hydrogen peroxide. The experiment demonstrated that the Bacillus stearothermophilus D value is higher against all others microrganisms tested proving that the use of this microrganism for the challenge is appropriate. It was also pertormed a test to guarantee that the stainless steel support is the most recommended one for this purpose, using supports of different materials normally found in the interior of the isolators (PVC, stainless steel, CKC, Teflon, polypropylene, latex, silicon, Hypalon, glass, nylon, aluminum foil) with 0,01 mL Bacillus stearothermophilus inoculum with the count of 102UFC/O,01 mL, that was properly veritied.