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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Functionalised ionic liquids for metal complexation

Alvarez-Vincente, Jorge January 2014 (has links)
This PhD is about novel functionalised ionic liquids with the ability to coordinate metals. These functionalised ionic liquids have the following functional groups; diphenylphosphine oxide (Ph2P=O) and phosphonate ((OEthP=O). The functional groups were grafted to different cations. The coordinating groups have been chosen for the coordination with rare earth elements and actinides. A detailed study of the coordinating abilities and the influence of the ionic species in the coordination chemistries has been performed and demonstrated . Phosphine oxide functionalised ionic liquids are an ionic version of well-known phosphine oxide ligands, commonly used to bind hard metals such as lanthanides or actinides. The phosphine oxide functionalised ionic liquids have been synthesised with two different anions, bis(trifluoromethylsulfonyl)imide and hexafluorophosphate. Different spacer units between the coordinating group and the cation have been synthesised and the influence of this spacer on the coordinating abilities of the ionic liquids was investigated. The crystal structures of some of the higher-melting ionic liquids with a phosphine oxide functionality were obtained and studied in detail in this thesis. The crystal structures of metal complexes with lanthanides were also obtained. Comprehensive simulation studies were also carried out to examine the charge distribution in these functionalised ionic liquids. In this work, structural data from the FILs and the metal complexes, such as crystal structures, UV-Vis absorption spectra and NMR complexation studies in the liquid state have been used to understand the coordination and the speciation of lanthanides and actinides in solution. Besides metal complexation studies with the functionalised ionic liquids, metal separation studies have been carried out . Hydrophobic FILs were used and coated on chromatographic silica in order to perform liquidsolid metal separations . The preliminary results of these experiments are shown and discussed in this thesis. Moreover, lanthanide salts have been mixed with phosphonium chloride salts in stoichiometric amounts resulting in novel compounds, lanthanide-containing chlorometallate ionic liquids. The physical properties, the structure and the luminescence properties of these liquid lanthanide complexes have been investigated.
32

The synthesis and transformation of novel lignin model oligomers

Forsythe, W. Graham January 2014 (has links)
Lignin is a complex, interlinked, non-repeating, heterogeneous bio-polymer found in wood which consists of phenylpropane subunits. The phenolic monomers of lignin are linked via various ether and carbon-carbon bonds. It is the second most abundant biopolymer after cellulose, accounting for 15-30 % of biomass and it has the potential to be a renewable source of small aromatic feedstock molecules. The synthesis of lignin model compounds plays an important role in both the elucidation of lignin's structure and in modelling the conditions required for the production of valuable feedstock molecules from lignin depolymerisation. The aim of the research presented in this thesis has been to provide an efficient route to multi-gram quantities of lignin model compounds which are more representative of lignin than the low molecular weight models typically employed in previously published work. The syntheses of several hexameric lignin models as well as an octamer, all of which contain three of the most common linkages in the native polymer have been carried out. The synthetic methodology used improves upon existing methods of preparing higher molecular weight lignin models in both overall yield and efficiency as well as practically on a multi-gram scale. Several of these compounds were then subjected to published procedures aimed at the transformation of lignin and model compounds into added value fine chemical intermediates. Extensive analysis of the major products was performed leading to some preliminary mechanistic insights into lignin oxidative and reductive depolymerisation chemistry.
33

Insight into selective oxidation of alcohol on Au-Pd catalysts : a DFT study

Liu, Jialong January 2014 (has links)
First-principles calculations within the density functional theory (DFT) framework were used to investigate selective oxidation of alcohol on Au-Pd catalysts. The selective oxidation of benzyl alcohol and 1 ,2-propanediol were studied, concerning mainly on the activity and selectivity, respectively.
34

Heterocyclic analogues of fluoranthene

Bedford, M. J. January 1973 (has links)
No description available.
35

Comprehensive study of semicontinuous emulsion polymerisation processes for producing nanoparticles

Chen, Yan January 2012 (has links)
Semicontinuous emulsion polymerisation offers flexibility and versatility for manufacturing colloids for a wide range of applications. The technique has been studied since 1950s, however, its importance has only recently realized as evidenced by increasing attentions it has received in recent years. Despite all attentions, the potentials of this process to produce novel materials have not been well recognized yet by polymer industry. The main aim of the thesis is to investigate the underlying mechanisms of semicontinuous emulsion polymerisation processes in order to improve and/or control the properties of resulting polymer latexes, and design new colloids. Polymerisations have been carried out in a jacketed glass reaction vessel. The conversions of monomers were measured by gravimetric method. Particle sizes and size distributions, their zeta potentials and molecular weights were measured by dynamic and static light scattering techniques. Turbidity as well as phase transition behaviour of latexes was measured by UV-visible spectroscopy. Glass transition temperature of polymers was measured by differential scanning calorimetry. Morphologies of particles were investigated by transmission electron microscopy and scanning electron microscopy. Semcontinuous microemulsion polymerisation of styrene has first been carried out in order to study the true features of nucleation stage. A major step has been taken forward to reconcile experimental data with theory. The average diameter of particles (D) decreased and the particle size distribution (PSD) narrowed with decreasing rate of monomer addition (Ra). Nanolatexes with extremely sharp particle size distribution with average particle size as small as 10 nm could be easily produced by the end of feeding. Consistent with recent theoretical developments, D at the end of nucleation was found to be independent of surfactant concentration ([5]). Furthermore, the average diameter of particles was successfully reduced by almost 25%. Thermosensitive and water-soluble poly(n-isopropylacrylamide) (polyNIPAM) colloids have recently attracted increasing attentions for many applications. A set of kinetic data has been reported for the batch polymerisation of neat NIPAM using a wide range of monomer and surfactant concentrations for the first time. A novel method has been applied to produce fast dissolving polyNIPAM latexes with high solids content, based on layered structures produced via semicontinuous process. The application of above method has been extended to fabrication of ultrafme thermal-sensitive nanocapsules. The core material produced via semicontinuous process could be easily and completely removed via self-removing process in water, in comparison with the conventionally made core material. Furthermore, the thickness of crosslinked polyNIPAM shells could also be precisely controlled via semicontinuous process. In recent years, considerable effort has been expended on research in polymer/silica core-shell hybrid systems due to their promising applications in surface coatings and biotechnology. Comparing with conventional batch process, hybrid particles obtained by semicontinuous surfactant-free emulsion polymerisation can incorporate more silica nanoparticles into the shell. The incorporation of silica nanoparticles into the shell can be further improved by gradually feeding silica dispersion during polymerisation. A mechanistic scheme for particle formation of hybrid particles under different pH has been developed. Monomers with intermediate water solubility like methyl methacrylate (MMA) can only produce stable composite particles at acidic conditions, at which silica nanoparticles are less stable. By contrast, more water-soluble monomers like vinyl acetate (VA) can easily yield composite particles at both basic and acidic conditions. Polymerisation on the surface of silica nanoparticles is believed to occur in the course of polymerisation for water-soluble monomers, which can suppress the electrostatic repulsion between both negatively charged silica and polymer particles and thus promote the adhesion of silica to polymer particles. For highly water-soluble monomers such as NIP AM, uniform silica armoured polyNIPAM particles could only be obtained under basic conditions. Interestingly, under acidic conditions, agglomeration of growing polymer particles with silica particles was extensive, resulting insoluble gels (even in the absence of crosslinker). TEM images revealed that under basic conditions, polymer-core/silica-shell structures were produced by batch process, but homogenous hybrids of polyNIPAM/silica nanoparticles by semicontinuous process.
36

Synthesis and reactions of sulfinimines

Sasraku-Neequaye, Leonid Kotei January 2010 (has links)
A large majority of drugs and drug candidates incorporate amine functionality and these include important compounds such as morphine, quinine and nicotine. N-Sulfinyl-imines (sulfinimines) are a versatile class of intermediates in organic synthesis particularly for the preparation of amines and amine derivatives. We herein report an efficient and cost effective one-pot synthesis of sulfinimines in enantiopure form (>99.8% ee) and in relatively high yields. In our investigations, we developed the scheme that involves the use of 1,2,3-oxathiazolidine-2-oxide derived from (1R, 2S)-(-)-norephedrine as a chiral auxiliary. Opening of the 1,2,3-oxathiazolidine-2-oxide with a mesityl Grignard reagent followed by treatment of the crude mixture with lithium hexamethyldisilasane afforded the mestyl sulfinamide in 72% yield and 76% recovery of the chiral auxiliary. As an extension to this scheme, when the crude reaction mixture obtained after addition of the lithium hexamethyldisilasane was treated with 1.1 equivalents of an aldehyde and three (3) equivalents of Ti(OEt)4 afforded the corresponding mesityl sulfinimines in high yields (>30 – 60%) and excellent enantiomeric excess (>99.8%). This to our knowledge is the first ever 3-step, one-pot syntheses of enantiopure sulfinimines using chiral aminoalcohol derived 1,2,3-oxathiazolidine-2-oxide as a chiral auxiliary. The mesitylsulfinamide thus produced was utilised in a novel free radical cyclisation reaction to yield mesitylsulfinyl protected enantiopure aminoindane in 68% yield.
37

Iron-catalysed dehydrocoupling/ dehydrogenation of amine- and phosphine-borane adducts

Vance, James R. January 2013 (has links)
This Thesis describes the investigations of iron-catalysed dehydrocoupling/dehydrogenation of various amine- and phosphine-borane adducts. Chapter 1 gives a general introduction to mam group element-element bond forming reactions, focusing on transition metal-catalysed dehydrocoupling under mild conditions. Chapter 2 describes the use of a series of iron precatalysts in the dehydrocoupling of Me2NRBH3. Analysis by liB NMR spectroscopy allowed the identification of various intermediates to be made. Furthermore, it was found that in the case of dinuclear Fe(I) complexes that they reduced in situ to afford Fe(O) nanoparticles which were the active catalyst. Interestingly, a related mononuclear Fe(II) complex was found to generate a homogeneous catalyst which, while also dehydrocoupling Me2NRBH3 to produce [Me2N-BH2h as the final product, favoured the formation of a different intermediate than was detected in the case of the Fe nanoparticles. Chapter 3 describes the use of the same iron precatalysts in the dehydrocoupling of MeNH2·BH3 and H3N·BH3. It was found that they were all active towards these adducts which demonstrated the versatility of the Fe catalysts. FUlihermore, various polymeric and oligomeric products were formed depending on which precatalysts were employed. Chapter 4 describes the synthesis of a series of Fe-phosphidoborane complexes. These were then employed as dehydrocoupling catalysts for a variety of phosphine-borane adducts. Although they were shown to be poor catalysts for the dehydrocoupling of secondary phosphine-boranes, increased catalytic activity was observed in the analogous reactions with primary phosphine-boranes. Polyphosphinoboranes of high molecular weight were yielded as the sole products. Chapter 5 describes the on-going investigation and possible future work based on the research described in Chapters 2-4.
38

An exploration of polymorphism in molecular compounds using high pressure

Fabbiani, Francesca P. A. January 2005 (has links)
A novel technique for the study of organic compounds under high pressure has been developed. This involves recrystallisation from solution under high-pressure conditions. Crystals grown using this technique have been characterised <i>in situ</i> by single-crystal X-ray diffraction. This novel high-pressure crystallisation technique has been demonstrated to be successful by growth of a single crystal of a new high-pressure polymorph of the polycyclic aromatic compound phenanthrene, from a dichloromethane solution at 0.6 GPa. A new polymorph of pyrene is also reported at 0.5 GPa. Structural analysis of the new high-pressure polymorphs of these two compounds shows that intermolecular interactions are substantially different from those found in the ambient-pressure structures and do not fit a previously established packing model. Recrystallisation of naphthalene in the 0.2-0.6 GPa pressure range did not result in the formation of a new polymorph, and its crystal structure is reported to be stable to compression to 2.1 GPa. A new monoclinic polymorph of acetamide has been prepared and structurally characterised from an aqueous solution at 0.8 GPa. The first 1:1 solvate of paracetamol with methanol has been crystallised from a methanolic solution at 0.6 GPa. The hydrogen-bonding pattern in this new structure has been compared and contrasted with patterns found in other solvates and polymorphs of paracetamol. It has been demonstrated how the systematic variation of pressure in combination with ambient-pressure polymorph screening can be used not only to identify rapidly all of the known polymorphs of the nootropic drug piracetam, but also to identify and characterise new polymorphs and hydrates.
39

Mechanistic studies into the reactions of diazonium and related compounds

Murray, Charles Douglas January 1974 (has links)
No description available.
40

Studies in the chemistry of some 1,3-bidentate reactive intermediates

Trattles, Michael James January 1974 (has links)
No description available.

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