Doctoral Degrees (Chemistry)
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Item Item Item The alkaloids of the Amaryllidaceae : the isolation and structures of two new alkaloids from Haemanthus natalensis and Nerine krigeii and contributions to the chemistry of coccinine : the absolute configuration of alkaloids based on the 5:10b-Ethanophenanthridine nucleus.(1960) Jeffs, P. W.; Warren, Frank Louis.No abstract available.Item The chemistry of river waters with special reference to the rivers of Natal.(1969) Kemp, P. Hayden.No abstract available.Item Studies of some new Euphorbiaceae diterpenes.(1971) McGarry, Joan Margaret.; Candy, H. A.The heartwoods of two species of South African Euphorbiaceae have been chemically investigated. From Cleistanthus schlechteri three new diterpenes possessing the hitherto unknown ent-isopimara-8(14),15-diene skeleton were isolated. By means of chemical and spectroscopic methods these were shown to be 3a-hydroxy-ent isopimara-8(14),15-diene, I, 3a-hydroxy-ent-isopimara- 8(14},15-dien-12-one, II, and 3a,12a-dihydroxy-ent-isopimara- 8(14),15-diene, III. A biogenetic sequence has been proposed in which it is suggested that these compounds are probably the precursors of the major diterpenoid, cleistanthol, IV, previously isolated from this source. From the second species, Spirostachys africana, a new diterpenoid seco-acid, spirostachic acid, VIII, was obtained in addition to the beyerene derivatives previously reported. Mass spectral fragmentation patterns of the seco-acid and its methyl esters proved to be useful as a diagnostic tool in structure elucidations.Item The chemistry of novel diterpenes from androstachys johnsonii Prain.(1973) Piacenza, Lorenzo Piero Luigi.; Pegel, Karl H.No abstract available.Item Extractives from the Meliaceae.(1979) Mulholland, Dulcie Aca.; Taylor, D. A. H.Abstract available in PDF file.Item The influence of primary and secondary nitrogen donor atoms on the thermodynamics of complex formation in aqueous solution.(1987) Martincigh, Bice Susan.; Marsicano, Fabrizzio.Item Investigations into the reactions of enamines and imines.(1990) Rae, Bruce.; Hickmott, Peter W.The alkylation of 2-methylcyclohexanone imines using methyl acrylate has been investigated with a view to optimising the reaction conditions. The mechanism of this alkylation reaction has been investigated and it has been shown that the alkylation does not proceed via a 2,6-intermediate which subsequently undergoes a rearrangement to the 2,2-product, but rather proceeds directly to the 2,2-product. As it had been shown that the alkylation of 2-substituted cyclohexanone imines in dry methanol occurred at the more substituted position, it was decided, in the light of certain apparently anomolous patent work, to investigate the alkylation of unsubstituted cyclohexanone imines using a variety of electrophilic alkenes. The results show that in certain instances, 2,2-bis-alkylation occurs and in others, mono-alkylation and that it is the strength of the electron-withdrawing group attached to the alkene which determines whether 2,2-bis-alkylation occurs or not. The reasons for this are discussed in the text. The preparation of a number of novel 2,2-bis-eyclohexanones and an octahydroquinoline are described. The reaction of I-phenyl-2-propen-l-one (phenyl vinyl ketone) with the benzylaluine imines of 2-butanone and I-phenyl-2-propanone in methanol gave gave two novel bicyclic diones, whereas the reaction between the benzylamine imine of 3-pentanone with I-phenyl-2-propen-l-one gave only mono-eyclic products only even though there appeared to be no impediment to the formation of the bicyclic compound. The structures were determined using nuclear magnetic resonance and confirmed by X-ray crystallography. The reaction between I-phenyl-2-propen-l-one and N-(l-phenyl-l-ethylidene)benzylamine gave after hydrolysis only the mono-substituted product, 1,5-diphenyl-l ,5-pentandione.Item An investigation of the solvent extraction kinetics of Germanium by 7- alkylated.-8-hydroxyquinoline extractants.(1990) Foster, Stephen James.; Salter, Leo F.Equilibrium and kinetic data for the solvent extraction of germanium by three impure commercial 7-alkylated-8hydroxyquinoline extractants which vary in structure at the 7alkyl group, are evaluated in order to elucidate an holistic kinetic extraction model which accounts for the various reactions and partition effects occurring during the metal-ion chelation process. It is proposed that for the extraction process, which is first order in germanium concentration, by the ligand reagents Lix 26, TN 01787 and TN 02181, the rate-determining step, on stereochemical grounds, is the attachment of either a neutral ligand or a protonated ligand species-to the biligand intermediate GeL2 2+ (L:ligand) at the interface. In high speed shaking/mixing assemblies the extraction process was observed to occur in two discrete reaction regimes : a fast initial rate for which the orders with respect to ligand reagent are 1,06, 2,10 and 1,77 for TN 02181, Lix 26 and TN 0178-7 respectively, and a slower subsequent rate for which the apparent reaction orders with respect to ligand concentration are 1,12, 2,70 and 3,08 for TN 02181, Lix 26 and TN 01787 respectively. For the slower reaction regime, orders between 1 and 3 are explicable if the steady state approximation is invoked for the intermediate germanium species GeL3+ and GeL2 2+ formed at the interface. In the fast reaction regime, it is proposed that the accelerated extraction rates are a function of (i) the speciation of germanium and (ii) participation in the rate-determining step by the protonated ligand moiety H2L+HS04- which is rapidly formed after phase contact. At low ligand concentration, the following order of ligand efficacy has been observed : TN 01787 < Lix 26 < TN 02181 whereas at high concentration ligand efficacies are similar because the interface is saturated with ligand. Orders with respect to [H+] for the reagents vary from -1 to - 3 during the course of reaction, indicating complex mixedorder behaviour. The effects upon extraction of ionic strength, temperature, the addition of organic modifiers and diluent nature are investigated as well as the kinetics of germanium stripping by aqueous hydroxide. The physical effects of interfacial tension, viscosity and relative dielectric constant are also reported and suggestions are made as to their effect upon the extraction characteristics. Computer modelling of the extractants has been used as an aid in describing size, structure and stereochemical considerations of the ligands and the chelate products.Item The redox and co-ordination chemistry of some dinuclear diphosphazane- bridged derivatives of ruthenium.(1991) Woollam, Stephen Farring.; Haines, Raymond John.Abstract available in pdf file.Item Investigations in dienamine chemistry.(1991) Simpson, Richard.; Hickmott, Peter W.Reaction of the pyrrolidine dienamines of ~1,8a-2-octalones with methyl vinyl ketone is complex. In methanol as solvent, the reaction occurs primarily with the linear dienamine isomer and results in annulation of the 8,8a-positions and, to a lesser extent, the 1,2-positions to give the corresponding octahydro-1 Hbenzo[d]naphthalene-2,10(3H,111-1)-dione and 3,4,5,6,7,8,8a,9-ctahydrophenanthren-2(10H)-one respectively. In toluene the dienamines react mainly in their cross-conjugated form. Diels-Alder addition of methyl vinyl ketone occurs across the 3,8a-positions to give the corresponding 9-acetylperhydro-2,4aethanonaphthalen-3-one and annulation of the 2,3-positions gives the 4,4a,5,5a,6,7,8,9-octahydroanthracen-2(3H)-one. The reaction of methyl vinyl ketone with the pyrrolidine dienamine of 4amethyl- 5-oxo-~ 1,8a-2-octalone is reported to give the aromatic product 3a, 7dimethyl- 2,3,3a,4,5,6-hexahydrophenalen-3,6-dionearisingfromp,o-annulation and in a related investigation with dienamines derived from isophorone it was reported that only products of Stork alkylation and Diels-Alder cycloaddition were isolated, there being no evidence for the reaction of methyl vinyl ketone with either the endo- or exocyclic o-positions of the dienamines. In an attempt to ascertain the reason for the apparently random changes in the regioselectivity of these related reactions some of this work was repeated and the reaction of methyl vinyl ketone applied to two other dienamines derived from 5,6,7,7a-tetrahydroindan-5-one and 4a,6-dimethyl-5-oxo-~1,8a-2-octalone. The reactions proved to be more complex than reported and several additional products have been isolated. Finally, reaction of phenyl vinyl ketone with dienamines derived from a1,8a_2-octalone was investigated. With the exception of the reaction of the 4amethyl dienamine, the main products isolated were those arising from addition of p.henyl vinyl ketone across the 3,8a-position to give the corresponding 9-benzoylperhydro-,4a-ethanonaphthalen-3-one. Reaction of the 4a-methyl dienamine with two equivalents of phenyl vinyl ketone gave a product tentatively assigned as the octahydrophenalenone. The mechanism of formation and spectral properties of the various products are discussed.Item Stereochemical aspects of the Baylis-Hillman reaction.(1992) Khan, Abdullah Ali.; Drewes, Siegfried Ernst.; Emslie, Neville Desmond.Item Stereoselective studies in the Baylis-Hillman reaction.(1992) Manickum, Thavrin.; Roos, Gregory H. P.Abstract available in pdf file.Item Asymmetric synthesis with an ephedrine based chiral auxilliary.(1992) Malissar, Dean Graham Shane.; Drewes, Siegfried Ernst.Abstract available in pdf file.Item Chemical constituents of plants native to Venda.(1993) Mashimbye, Mahlori Jeffrey.; Drewes, Siegfried Ernst.Abstract available in pdf file.Item Isolation and identification of novel compounds from indigenous plants.(1993) Sehlapelo, Bethuel (Tiny) Matshene.; Drewes, Siegfried Ernst.Abstract available in pdf file.Item Structure and stereochemistry of compounds from Cassipourea species.(1993) Taylor, Craig William.; Drewes, Siegfried Ernst.Abstract available in pdf file.Item Ruthenium and silver complexes of potentially binucleating phosphoruspyridyl and phosphorusbipyridyl ligands.(1994) Parry, Campbell John.; Haines, Raymond John.; Field, John Stainer.Abstract available in pdf file.Item Dicopper and dirhodium phosphorusbipyridyl ligand-bridged complexes : electrocatalysts for carbon dioxide reduction.(1994) Sookraj, Sadesh Harichand.; Haines, Raymond John.Abstract available in pdf file.