The current environmental situation, with respect to global warming and the ever– approaching depletion of fossil fuel sources, places significance on the development of green fuel and platform chemical production methods. In this context, processes that utilise biomass sources as feedstock, are of great interest. Cellulose, which is the most abundant biopolymer in nature, is a renewable low–cost carbon resource derived from harvest residues and sources like wood and straw. Glucose generation from cellulose requires a saccharide conversion, whereby the β-(1,4)-glycosidic bond linkages in the cellobiose polymer repeating units are cleaved. Problems arise in the hydrolysis of cellulose as experimental and theoretical studies have shown cellulose to have very low solubility in water and most other general molecular solvents. This results in the use of harsh pretreatments at high temperatures and pressures to extract cellulose from lignocellulosic material and strong acids catalysts (pKa < −3.2). Room temperature ionic liquids (RTILs) provide potentially environmentally friendly alternative. It has been shown that ILs can dissolve cellulose under relatively benign conditions and can possibly be adapted into a one-pot-like process of hydrolysis using acid-functionalised IL catalysts. This dissertation investigated the effect of various ionic liquids on the thermodynamics of cellobiose acid hydrolysis, as both a catalyst and as a solvent, using computational means. An appropriate thermodynamic cycle protocol, a DLPNO-CCSD(T)/ccpVTZ//TPSS/def2-TZVP [M05-2X/6-31+G** (SMD)] proton exchange cycle, was established through benchmarking for the prediction of Brønsted acid-functionalised ionic liquid pKa values in ionic liquids. The sulfonyl-functionalised acidic IL was shown to be the most acidic IL resulting in a lower protonation free energy. Solvation in ionic liquids resulted in higher protonation and barrier height free energies relative to solvation in water. The current environmental situation, with respect to global warming and the ever– approaching depletion of fossil fuel sources, places significance on the development of green fuel and platform chemical production methods. In this context, processes that utilise biomass sources as feedstock, are of great interest. Cellulose, which is the most abundant biopolymer in nature, is a renewable low–cost carbon resource derived from harvest residues and sources like wood and straw. Glucose generation from cellulose requires a saccharide conversion, whereby the β-(1,4)-glycosidic bond linkages in the cellobiose polymer repeating units are cleaved. Problems arise in the hydrolysis of cellulose as experimental and theoretical studies have shown cellulose to have very low solubility in water and most other general molecular solvents. This results in the use of harsh pretreatments at high temperatures and pressures to extract cellulose from lignocellulosic material and strong acids catalysts (pKa < −3.2). Room temperature ionic liquids (RTILs) provide potentially environmentally friendly alternative. It has been shown that ILs can dissolve cellulose under relatively benign conditions and can possibly be adapted into a one-pot-like process of hydrolysis using acid-functionalised IL catalysts. This dissertation investigated the effect of various ionic liquids on the thermodynamics of cellobiose acid hydrolysis, as both a catalyst and as a solvent, using computational means. An appropriate thermodynamic cycle protocol, a DLPNO-CCSD(T)/ccpVTZ//TPSS/def2-TZVP [M05-2X/6-31+G** (SMD)] proton exchange cycle, was established through benchmarking for the prediction of Brønsted acid-functionalised ionic liquid pKa values in ionic liquids. The sulfonyl-functionalised acidic IL was shown to be the most acidic IL resulting in a lower protonation free energy. Solvation in ionic liquids resulted in higher protonation and barrier height free energies relative to solvation in water.

No description available.

A survey of substitution reactions conducted in a phosphonium bistriflimide ionic liquid is presented. The results demonstrate high selectivity favoring substitution over typically competitive elimination and solvolytic processes even when challenging secondary and tertiary electrophiles are employed. The first reports of Kornblum substitution reactions in an ionic liquid are described that proceed with very high chemoselectivity in favor of nitro over nitroso products and elimination side products. The structure-reactivity study indicates that these reactions proceed through a narrow spectrum of pathways ranging from straight SN2 to a preassociation pathway along a saddle point that approaches the SN1 limit. The lack of any basic entity in the phosphonium bistriflimide ionic liquid appears to prevent any potential base-mediated elimination reactions, which makes this a highly selective medium for use in general substitution reactions. A general, high yielding procedure is described for the esterification of carboxylic acids through carboxylate alkylation in phosphonium salt ionic liquid. The product ester can be readily isolated using a standard extraction protocol or by direct solvent freedistillation allowing ionic liquid re-use. The reaction takes place at relatively low temperature in comparison to other processes reported in ionic liquids. Biologically important BZE (benzoate) esters were synthesized and a proposed solvolysis mechanism investigated in ionic liquids. The Pd-mediated Buchwald-Hartwig amination reaction of aryl halides in phosphonium salt ionic liquid consisting of a trihexyl(tetradecyl)phosphonium cation with a range of anions has been investigated. A pronounced anionic effect was uncovered with the reaction proceeding readily with weakly nucleophilic diarylamines only in the presence of non-coordinating anions. A mechanism is postulated to explain these results involving a rate limiting ligand exchange step that proceeds through a dissociative pathway. A novel non solvated crystal structure of tris(dibenzylideneacetone) palladium(0) in phosphonium salt ionic liquids is reported. This research provided insights concerning the use of ionic liquids in palladium catalyzed Buchwald-Hartwig amination reaction. New synthetic methods were developed for the preparation of trialkyl (methyl) phosphonium ionic liquids, with this novel "green" protocol, the use of iodomethane is eliminated and oxidation of trialkyl phosphines can be reduced. / Thesis / Doctor of Philosophy (PhD)

<p> Using a potentiometric method on 10^-4M and 10^-5M Al(NO3)3 solutions at constant ionic strength (0.1 M KNO3) and temperature (25°C), titration curves were defined and examined with respect to three variables (total aluminum concentration, pH range, and time) in order to assess the reversibility of the aqueous system.</p> <p> Increasing pH titration interval decreased reversibility while increasing time interval led to a slight increase in reversibility. Decreasing the total aluminum concentration also slightly improved reversibility. Overall, the reversibility of the system was observed to be poor.</p> <p> Computer models were compared to experimental titration data in order to derive the speciation schemes which best fit the data. Polynuclear hydrolysis schemes fit the data best for the concentration levels as follows: Al^3+, Al(OH)4^-, and Al6(OH)15^3+ for 10^-5M Alt. Al^3+, Al(OH)4^-, and Al8(OH)20^4+ and/or Al13(OH)32^7+ for 10^-4M Alt. / Thesis / Master of Science (MSc)

Various innovative separation methods in chromatography have been proposed. The interaction of the 4-t-butylphenyl group with b-cyclodextrin is well-known; compounds tagged with the 4-t-butylphenyl group are separated from untagged compounds using b-cyclodextrin column. In this study, increasing the chain length of tagged molecules does not increase the retention time but depends on other functional groups present, while increasing the number of tags in a molecule increases retention time. The t-butyl group was also compared to adamantyl and lithocholic acid tags. In-house b-cyclodextrin columns were synthesized to observe the effect of the linkage of the cyclodextrin molecule to the support. Furthermore, tagged products could be separated from the starting materials using in-house columns employing flash b-cyclodextrin. Supported room temperature ionic liquids (SILs/MSILs) were explored for the extraction of polyunsaturated triacylglycerols (PUTAGs).Various room temperature ionic liquids (RTILs) with silver salts were tested for extraction effectiveness.The most hydrophobic RTIL [Hmim][PF6] in this study, with dissolved AgBF4 proved to be the best combination for effective extraction. RTILs supported on silica gel and mesoporous SBA-15 reacted with silver salts (psorbents) were synthesized and characterized. The later support revealed a conserved mesopore structure by SEM, TEM, SAXS and N2 isotherms. Trilinolenin (tri-18:3) quantification was explored by conversion to polyunsaturated fatty acid alcohols and methyl esters, Proton NMR spectroscopy and by non-aqueous reverse phase (NARP)-HPLC with evaporative light scattering detector (ELSD). Tri-18:3 and its free fatty acid (FFA-18:3) were extracted selectively and quantified using a two-step methodology. The extraction of a-tocopherol with RTILS modified with organic anions was also successfully demonstrated. Finally, studies of chiral stationary phases with on-resin cyclic oligoprolines were demonstrated. Cross linking of linear oligoprolines was shown to disrupt the poly-proline helix (II) thus leading to lower number of analytes resolved. On-resin cyclic oligoproline synthesis was successful for penta- and tetraproline but failed for the triproline. PyBOP/HOBt/DIPEA was employed for effective cyclization. The on-resin cyclic oligoproline CSP showed a lower number of resolved analytes, implying the importance of the poly-proline helix for chiral selectivity. The innovative separations in this study serve as starting points for developing mature separation methods.

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The thin film pressure balance (TFPB) technique were used to study the stability of single foam films produced in the presence of n-alkyl polyoxyethylene (CnEOm) homologues. The results showed that films thin faster than predicted by the classical DLVO theory, which considers contributions from the van der Waals-dispersion and double-layer forces to the disjoining pressure of the film. The discrepancy may be attributed to the presence of hydrophobic force, the magnitude of which has been estimated using the Reynolds lubrication approximation. It has been found that the attractive hydrophobic force was substantially larger than the attractive van der Waals force, which may explain the faster film thinning kinetics. With a given non-ionic surfactant, the hydrophobic force decreased with increasing surfactant concentration, which explained the slower kinetics observed at higher concentrations and hence the increased foam stability. At concentrations where the hydrophobic force became comparable to or smaller than the van der Waals force, the foam films were stabilized by the increased elasticity of the foam films. The film elasticity of the surfactant solutions were measured using the oscillating drop analysis technique at different frequencies. The measurements were conducted in the presence of CnEOm surfactants with n=10-14 and m=4-8, and the results were analyzed using the Lucassen and van den Tempel model (1972). There was a reasonable fit between the experiment and the model predictions when using the values of the Gibbs elasticity calculated from the Wang and Yoon model (2006). From this exercise, it was possible to determine the diffusion coefficients (D) of the CnEOm surfactants. The D values obtained for CnEOm surfactants were in the range of 2.5x10-10 to 6x10-9 m2s-1, which are in general agreement with those reported in the literature for other surfactants. The diffusion coefficient decreased with increasing alkyl chain length (n) and increased with increasing chain length (m) of the EO group. These findings are in agreement with the results of the dynamic surface tension measurements conducted in the present work. The TFPB studies were also conducted on the foam films stabilized in the presence of a mixture of C12EO8 and sodium dodecylsulfate (SDS) at different ratios. The results showed that the hydrophobic force increased with increasing C12EO8 to SDS ratio. Thus, the former was more effective than the latter in decreasing the hydrophobic force and hence stabilizing foam films. The C12EO8 was more efficient than SDS in increasing the elasticity of the single foam films and stabilizing foams. The TFPB studies were also conducted in the presence of n-octadecyltimethyl chloride (C18TACl) and polymers, i.e., polyvinylpyrrolidone (PVP) and polystyrene sulfonate (PSS). The effect of polymer on the film elasticity was strongest in the presence of PSS, which can be attributed to the charge-charge interaction. Nano-sized silica and poly methyl methacrylate (PMMA) particles were used as solid surfactants to stabilize foams. It was found that the foam stability was maximum at contact angles just below 90o. The TFPB studies conducted with silica nano-particles showed that the kinetics of foam films became slower as the contact angle was increased from 30o to 77 o , indicating that foam films becomes more stable with more hydrophobic particles. The extra-ordinary stability observed with the hydrophobic silica nano-particles may be attributed to the possibility that the particles adsorbed on bubble surfaces retard the drainage rate and prevent the films to reach the critical rupture thickness (Hc). Confocal microscope and SEM images showed that hydrophobized nano-particles adsorbed on the surfaces of air bubbles, and that some of the nano-particles form aggregates depending on the particle size and hydrophobicity. The dynamic surface tension measurements conducted with PMMA and silica nano-particles showed that the latter has higher diffusion rates than the former, which may be due to the differences in particle size and hydrophobicity. / Ph. D.