Alkane-rich fractions including n-paraffins are the most important chemical feedstock used in the / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2008.

Milling data from sugar factories in Mauritius were examined from 1960 to 2004 to assess the trend in the quality of cane received at mills and the change in factory performance. A deterioration in overall quality was apparent due to the increased level of extraneous matter delivered in the cane supply. Comparison was made with available data from other countries in the world, notably those of South Africa and Australia. Controlled addition of extraneous matter to clean cane was effected under laboratory conditions to determine the relative impact of dry leaves, green leaves and cane tops on the quality of cane and the resulting juice, and to predict through derived equations, their impact on cane processing. The addition of dry leaves was found to have the most adverse effect followed by green leaves and cane tops. In the case of dry leaf addition to cane the detrimental effects were found to be masked by an increase in the concentration of solutes in the juice extracted. This phenomenon was thought to be due to the selective sorption of water (so-called Brix-free water) by dry leaves. To test this assertion, the sugar cane stalks of four different cane varieties aged 52, 44 and 36 weeks were separated into their component parts by means of a method devised in this work. There were nine component parts: stalk fibre, stalk pith, rind fibre, rind fines, top fibre, dry leaf fibre, dry leaf fines, green leaf fibre and green leaf fines which, on characterisation by Fourier transform infrared spectroscopy and scanning electron microscopy, were very similar except that stalk pith was more flaky and had a higher surface area than the others. Various analytical techniques were tested for the determination of Brix-free water. The most convenient method proved to be a refractometric method which was improved so as to be applicable to the wide range of cane components fibres studied. Statistical analysis of the Brix-free water content of the separated samples showed that when the combined effect of fibre and pith in the cane stalk of three ages was considered, the four cane varieties were not different. This was not the case for dry leaf, green leaf, top and rind. Of the nine cane components, stalk pith exhibited the highest Brix-free water value of about 20 g/100 g fibre, whereas all the other components exhibited values of about 15 g/100 g fibre, which are much lower than the traditionally accepted value of 25% for cane. The latter was found to be the fibre saturation point of bound water determined at 20 oC, which is the sum of dissolved and hydrated waters, and which is normally greater than the Brix-free water value as determined in this work. The water sorption characteristics of the various cane component parts were further investigated by making measurements to determine the equilibrium moisture contents at various water activity values. These data were used to construct adsorption isotherms. These were fitted to 17 existing isotherm models, of which two, namely, the Hailwood-Horrobin and Guggenheim-Anderson-de Boer models, gave the best fit. The sorbed water was subsequently characterised in terms of various parameters, namely, the monolayer moisture content, the number of adsorbed monolayers, the percentage of bound water, the total surface area for hydrophilic binding, the heats of sorption of the monolayer and multilayers, the net and total isosteric heats of sorption and the entropy of sorption. From the monolayer moisture content and the amount of “hydrated water” as calculated from the Hailwood-Horrobin model, it is clear that at EMC values between 0 and 5% (aw = 0 – 0.3), the non-freezable water is tightly bound to the surface of the fibre. The second region starts at EMC values from 5% to 10 – 15% (aw = 0.3 to 0.6 – 0.8) depending on the cane components, and the bound water in this region is termed the freezable water. The third type of water is essentially free water, it exists after the second region and ends at EMC values of about 25%. From this study, it is apparent that the Brix-free water as measured in this work measures the amount of water bound in the first two regions. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2008.

The compounds [Cp(CO)3W{(CH2)nX}] (X = Br, I; n = 3 - 6) were prepared in high yield by the reaction ofNa[Cp(CO)3W ] with Br(CH2)nBr. The bromoalkyl compounds were subsequently reacted with NaI to give the corresponding iodoalkyl complexes. The crystal structures of [Cp(CO)3W{(CH2)sI}] and [Cp(CO)3W{(CH2)3Br}] are reported for the first time. The former compound forms orthorhombic crystals in the space group P21nb and the latter forms triclinic crystals in the space group PI. Both have W-C bond lengths of2.35 A. The C-I bond length is 2.12 A; the C-Br bond length is 1.94 A. In a similar manner to the above, the compounds [Cp(CO)2(PPhiMe3 - i)Mo{(CH2)nBr}] (Cp = TJs-CsHs, n = 3, 4; i = 0 3) and [Cp*(CO)3Mo{(CH2)nBr}] (Cp* = TJs-CS(CH3)s,n = 3, 4) were prepared in medium to high yield by the reaction of the corresponding anion [Cp(CO)2(PPhjMe3-i)Mor or [Cp*(CO)3Mor with Br(CH2)nBr. The bromoalkyl compounds were subsequently reacted with NaI to give the corresponding iodoalkyl compounds [Cp(CO)2(PPhiMe3 _i)Mo{( CH2)nI}] (n = 3, 4; i = 0 - 3) and [Cp*(CO)3Mo{(CH2)nI}] (n = 3, 4) respectively. The iodoalkyl compounds were also prepared by the reaction of the corresponding anion and a,O)diiodoalkane in much lower yields. These compounds have been fully characterised and their properties are discussed. The crystal and molecular structure of [Cp(CO)2(PPh3)Mo{(CH2)3I}] is also reported, again for the first time. The compound forms crystals in the monoclinic space group P21/n; with a Mo-C bond length of 2.40 Aand a C-I bond length of 2.13 A These halogenoalkyl compounds were used as precursors to the new heterobimetallic complexes [Cp(CO)3W(CH2)nMo(CO)3Cp] n = 3 - 6; [Cp(CO)3W(CH2)nMo(COhCp*] n = 3,4; [Cp(CO)3W(CH2)nMo(CO)2(PPhiMe3_i)Cp] n = 3,4; i = 0 - 3 and [Cp(CO)2Fe(CH2)nMo(CO)2(PPhiMe3_i)Cp] n = 3,4; i = 0 - 3. The heterobimetallic complexes were prepared by the direct displacement of the iodide of a metallo-iodoalkyl complex with the appropriate anion. The complexes have been fully characterised by IR, IH NMR, 13C NMR, COSY, HETCOR or HSQC and elemental analyses. X-ray diffraction studies are for the first time reported for the complexes [Cp(CO)3W(CH2)3Mo(CO)2(PPh3)Cp] and [Cp(CO)2( PPh3)Mo(CH2)3Fe(CO)2Cp]. Both compounds form monoclinic crystals in the space group P 2I/c. The former, with a W-C bond length of2.32 Aand Mo-C bond length of2.35 Aand the latter with a Mo-C bond length of2.37 A and Fe-C bond length of2.08 A. The reactions of some of the above halogenoalkyl compounds with some simple inorganic molecules were investigated. The reactions of [Cp(CO)3W{CH2)4Br}] and [Cp(CO)2(PPhMe2)Mo{(CH2)3Br}] with silver nitrate in acetonitrile formed orange products, [Cp(CO)3W{(CH2)40N02}] and [Cp(CO)2(PPhMe2)Mo{(CH2)30N02}] respectively. The compounds [Cp(CO)3W{(CH2)sCN}], [Cp(CO)3W{(CH2)4CN}], [Cp(CO)2(PPhMe2)Mo{(CH2)3CN}], [Cp(CO)3W{(CH2)4N3}], [Cp(CO)3W{(CH2)sN3}], [Cp(CO)2(PPhMe2)Mo{(CH2)3N3}] were also obtained from various reactions using the reagents; AgCN, KCN, NaCN and NaN3. Similar reactions with molybdenum analogs gave cyclic carbene compounds. Reaction studies were also done on some of the above heterobimetallic compounds with tertiary phosphines; carbon monoxide gas and trityl salt, and thermolyses were also investigated. The reactions of PPh3 with [Cp(CO)3W{(CH2)3}MLy] {MLy = MO(CO)3Cp, MO(CO)3Cp* and MO(CO)2(PMe3)Cp} were found to be totally metalloselective, with the phosphines always attacking the expected metal site predicted by the reactions ofthe corresponding monometallic or homodinuclear alkyl species. A similar reaction involving CO with [Cp(CO)3W(CH2)3Mo(CO)3Cp] and [Cp(COhFe(CH2)3Mo(CO)2(PMe3)Cp] was also metalloselective. The reaction of [Cp(COhFe(CH2)4Mo(CO)3)Cp*] with trityl salt gave the expected complex [Cp(CO)2Fe(C4H7)Mo(CO)3)Cp*]PF6. It is believed that the structure of the trityl salt complex has the iron atom n-bonded whilst the molybdenum is cr-bonded to the butyl chain. The compounds [Cp(CO)3W(CH2)3Mo(CO)3Cp*] and [Cp(CO)2Fe(CH2)3Ru(CO)2Cp] both gave cyclopropane on thermolysis, indicating a ~elimination and reductive processes taking place. The crystal structure of [Cp(CO)3W{(CH2)3COOH}], which was obtained in one of the reaction studies, where the compound [Cp(CO)3W(CH2)3Mo(CO)2(PMe3)Cp] was reacted with excess PPh3in acetonitrile, is reported. / Thesis (Ph.D.)-University of Natal, Durban, 2002.

The theoretical and experimental work in this thesis is primarily aimed at i) the quantification of the strengths of a number of hydrogen bonded systems, and ii) exploring the relationships that exist between the various physico-chemical properties determined in this study, which are related to the hydrogen bonding phenomenon. To this end a three part study of some hydrogen bonded systems has been undertaken. The study involves using a number of theoretical and experimental procedures, including a theoretical ab initio molecular orbital study, infrared spectroscopic determinations and a thermodynamic investigation involving measuring enthalpies and volumes of mixing and applying a theoretical model of interacting liquid mixtures. Conclusions based on ab initio molecular orbital theory, thermodynamic and infrared spectroscopic results conducted in this work include: i) the proton donating ability of the three hydrogen donor moieties studied in this work decreases in the order O-H > N-H ~ S-H, ii) the proton accepting competence of the three electron donor atoms considered in this work decreases in the order N > 0 > S in all cases except in the liquid phase systems involving dipropylamine and propane-1-thiol as proton donors, where the proton accepting ability of the atoms is in the opposite order i.e. S > 0 > N, and iii) a direct correlation exists between the shift in the A-H stretching wavenumber and the hydrogen bond interaction energy. . Although a number of factors influence the stability of the hydrogen bond, it was also tentatively concluded that in liquid phase systems involving weakly self-associated hydrogen bond donor molecules, the available surface area of the proton accepting atom becomes the dominant strength determining factor, otherwise factors such as basicity and electronegativity dominate. / Thesis (Ph.D.)-University of Natal, Durban, 1995

The oxidative dehydrogenation of alkanes provides a potential route to higher value products such as olefins and aromatic compounds. Alkanes are of low environmental impact and their increasing availability has prompted extensive research in the field of alkane activation. The use of hydrotalcite-type compounds (HTlc), to achieve such reactions, has received much attention over recent years. Specifically, hydrotalcites and hydrotalcite-like compounds are promising catalysts because they provide a route to mixed-metal oxides with variable composition and significantly high metal-oxide distribution. Vanadium containing hydrotalcite-like catalysts were synthesized via the co-precipitation route and doped with either barium, cesium or boron using the wet impregnation method. These catalysts were characterized using electron microscopy, inductively coupled plasma - optical emission spectroscopy, X-Ray diffraction, differential thermal analysis, BET surface area measurements and infrared spectroscopy. The catalysts were then tested in a fixed bed reactor using n-octane as the feed and air as the oxidant. The effect of fuel-air ratios and contact time was studied on the unpromoted Mg-V-HTlc. The conversion of n-octane and the selectivity and yields to the products were quantified using gas chromatography and used to determine optimum reaction conditions. The effect of promoters on the conversion of n-octane and the selectivity of the catalyst in terms of products was determined under the optimum reaction conditions. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2010.

Carbamate chemistry has flourished since the 1980's which saw the introduction of the carbamoyl group by Hoppe and co-workers, prominent researchers in this area, as a suitable moiety for the activation and stabilisation of alpha-heterocarbanions which are important intermediates in synthetic organic chemistry. This functionality increases a-CH acidity and stabilises the a-lithiocarbanion thus generated. The versatility of the carbamate group has spawned investigations into the numerous possibilities that exist for the functionalisation of the carbon alpha to the carbamate group. Some of these possibilities were explored in the present work. The direct formation of stable benzylic carbanions alpha to an oxygen atom is not a facile process as such lithiated species are unstable and readily undergo a 1,2-Wittig rearrangement. However, protection of the alcohol as the carbamate enabled functionalisation of both benzylic sites with a variety of electrophiles. Benzyl carbamates were found to react regioselectively with a,~-unsaturated electrophiles to afford either the 1,2- or l,4-addition products. The regioselectivity could be controlled by the presence or absence of a silyl moiety, either a trimethylsilyl or tertbutyldimethylsilyl moiety, attached at the benzylic position, alpha to the carbamate. The reaction of benzyl carbamates with 2-cyclohexen-1-one and 2-butenolide afforded the 1,2-addition adducts in moderate to good yields (25-66%). The isolation of the masked ahydroxy ketone resulting from the opening of the lactone ring on reaction of 2-butenolide with benzyl N,N-diisopropylcarbamate was surprising, as this electrophile is known to behave as an excellent Michael acceptor. The introduction of a silyl moiety at the benzylic position facilitated conjugate addition, yielding the corresponding Michael addition products. A novel cyclisation was observed on reaction of a-silyl benzyl carbamates with methyl acrylate to give the a,y;y-trisubstituted butanolides (y-butyrolactones). The proposed vii mechanism of this reaction is discussed and illustrates the migrational ability of the carbamate functionality. Chiral induction in benzylic systems has only been investigated by a few authors. In the present investigation two possible routes to chiral induction at the benzylic position were investigated using either a (-)-sparteine-mediated transformation or chiral carbamates derived from (L)-proline. (-)-Sparteine mediated transformations were solvent dependent with the best enantiomeric excess of 28% being obtained. The results indicated that racemisation at the benzylic position was faster than reaction with an electrophile. The chiral carbamates were only slightly more successful yielding the a-substituted adducts with diastereoselectiVities of the order of 20-50%. The diastereoselectivities were found to be enhanced by the addition of HMPA which coordinated with the transition state blocking one of the faces to attack by the electrophile. The 1A-addition reaction with 2-butenolide was particulary useful as it allowed the exploration of the synthesis of lignan derivatives from benzyl carbamates. Lignans are secondary plant metabolites and exhibit.a wide range of biological activities. Applying the methodology developed to the synthesis of lignans resulted in the preparation of an arylnaphthalene lignan, in 79%, and the partial synthesis of racemic fargesin, a racemic furofuran lignan. This natural product synthesis highlighted the difficulty in removing the carbamate functionality and re-introducing the alcohol moiety. Thus, hydrolytic cleavage of the benzyl carbamates was investigated using a selection of mineral acids. Depending on the reaction conditions, the products were found to be the corresponding benzyl alkanoates or benzylhalides. The alkanoates are derived from nucleophilic displacement of the initially formed benzyl halide A novel deprotection of a-silyl benzyl carbamates was also observed in which the carbamoyl group was cleaved to afford the a-silyl alkanoates and chlorides without the loss of the silicon moiety. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1997.

The contents of this thesis are divided into two separate parts, both of which are concerned with optical phenomena for light propagation through source-free nonmagnetic media. Considered in the first part are various theoretical investigations pertaining to nonmagnetic crystals. While the second part focuses specifically on the experimental investigation of the quadratic electro-optic effect in some crystals of the KDP family. The opening theoretical chapters of this thesis are based aln10st entirely on four publications which are the result of work completed in this PhD study. These papers~ in the order that they appear in the following chapters, are: Systematic Eigenvalue Approach to Crystal Optics: An Analytic Alternative to the Geometric Ellipsoid model (Gunning and Raab 1998a); Algebraic Determination of the Principal Refractive Indices and Axes in the Electrooptic Effect (Gunning and Raab 1998b); Physical Implications of the Use of Primitive and Traceless Electric Quadrupole moments (Gunning and Raab 1997a); and Electric-Field-Induced Optical Activity in Nonmagnetic Crystals (Gunning and Raab 1997b). In later chapters two separate experimental projects on the quadratic electro-optic effect in KDP-type crystals are described. Some of the results of these investigations have yet to be published, while others, for both the interferometric and polarimetric experiments, appear in the papers: The Quadratic Electrooptic Coefficient gxxxxgyyxx of DKDP Crystals (Gunning et al. 1998a); The Quadratic Electrooptic Effect and Estimation of Antipolarization in ADP (Gunning et al. 1998b); and Studies of the Quadratic Electrooptic Effect in KDP-type Crystals (Gunning et al. 1999). The first chapter introduces a multipole eigenvalue theory of light propagation through a nonmagnetic anisotropic dielectric. This theory, in the appropriate multipole order, explains a range of optical phenomena, including circular birefringence and the linear birefringences of Jones and Lorentz, not otherwise fully explained by the widely-used Fresnel ellipsoid or related indicatrix ellipsoid. By means of this model the birefringences, optic axes, and eigenpolarizations of light propagating through a transparent medium are fully accounted for. The theory presented here concentrates on the electric-dipole description, which is the formal basis of the ellipsoid models, and the description of the birefringences, optic axes, and eigenpolarizations is algebraic, rather than geometric, and in terms of measurable crystal property tensors. Chapter 2 follows the multipole approach of Chapter 1 with a systematic algebraic means to derive expressions for the principal refractive indices and dielectric axes of a source-free nonmagnetic crystal in a uniform electric field. This is seen as a preferred alternative to the more common iterative numerical approaches to the problem. Results obtained in this chapter, to the chosen order in the field, are again expressed algebraically in terms of crystal property tensors. A number of illustrations of the approach are given for the linear electro-optic effect in crystals of the symmetry point groups 43m, 3m, 42m, and 1. Also, to demonstrate the inadequacies of the numeric method, the quadratic effect in 42m is investigated. Throughout these examples, comparisons are drawn with published numerical results. Chapters 3 and 4 start to allow for higher-order multipole moments, in contrast to the opening two chapters which are limited to the electric-dipole description. Specifically, electromagnetic effects to the order of electric quadrupole and magnetic dipole are considered. Since these effects, such as chiral phenomena in fluids and crystals and gyrotropic birefringence in antiferromagnetic crystals, require for their full description the inclusion of electric quadrupoles, the nature of the electric-quadrupole moment is considered in Chapter 3. In many theories this moment is defined to be traceless, but this chapter shows that when this definition is used in the derivation of a wave equation to describe light propagation through an optically active uniaxial medium, this equation as well as properties derived from it, in particular the refractive index of the eigenpolarizations, are in general dependent on the origin used to define the Inoment. This is physically unacceptable for the theoretical expression of an observed effect. It is shown that if the primitive definition of the quadrupole monent is used in this theory instead, this difficulty does not arise. Also to the order of electric quadrupole and magnetic dipole, Chapter 4 presents a macroscopic theory of electric-field-induced optical activity in source-free nonmagnetic crystals. In this approach a wave equation, to this multipole order and including distortions linear in an applied electric field, is derived which allows for the description of the linear electric-field-induced circular birefringence. It also identifies other coexisting birefringences, both natural and fieldinduced which are described in this multipole order. All these birefringences are expressed in terms of measurable crystal property tensors. In this chapter, nonmagnetic crystal classes are identified which exhibit this field-induced optical activity for particular light-propagation and applied-field configurations for light waves with purely transverse fields. These crystals, symmetry considerations, and other coexisting natural and field-induced birefringence are presented in Table 4.1. The first chapter of Part 2 of this thesis introduces the quadratic electro-optic effect in KDP-type crystals and provides motivation for the present experimental inquiry of the effect. Tabulated are previous experimental results for components of the quadratic electro-optic coefficients of crystals of KDP, ADP, and DKDP investigated in this work. Also introduced is the electrostrictive effect in these crystals, since it plays a part in the experimental determination of quadratic electro-optic coefficients of these crystals, and values for coefficients of this effect are listed. A multipole theory, based on that in Chapters 1 and 2 to the order of electric dipole and allowing for perturbations quadratic in a low-frequency applied electric field, is presented which describes fully the observed quadratic electro-optic effect in these crystals for the lightpropagation and applied-field geometries of interest. The analytic results derived for the observed induced refractive index changes for the polarization eigenvectors for a particular propagation path through the medium are expressed in terms of the quadratic electro-optic coefficients gxxxx,gyyxx, and gxxxx, One of the two methods proposed in this work for the measurement of coefficients of the quadratic electro-optic effect in specimens of KDP-type crystals is the interferometric technique. Chapter 6 serves to introduce this approach and to provide the theoretical basis for it, within the context of determining small induced phase changes. After a number of experimental factors are highlighted the method proposed for this work is explained. Specifically, this approach utilizes a Michelson arrangement, invoking active stabilization against low-frequency noise influences, and the coefficients are measured by phase-compensation means. This apparatus and its various components is then fully described in Chapter 7, including the method for its operation. The results of this interferometric research appear in Chapter 8 for the various light-propagation and applied-field geometries used, and values are presented for the individual coefficients gxxxx, gyyx.x, and gxxx.x in KDP and ADP, and also the electrostrictive coefficients Yxxyy and Yxxxxin the same crystals. An explanation of the second approach to measure quadratic electro-optic coefficients in this work, the dynamic polarimetric technique, is given in Chapter 9. Two proposed means to investigate the KDP-type crystals by this approach are described and explained theoretically, and the layout of the apparatus and its various components is highlighted. Results of this polarimetric investigtion for two light-propagation directions are given in Chapter 10 for investigations on KDP, ADP, and DKDP single crystals. These give values for the difference in quadratic electrooptic coefficients |gxxxx - gyyxx| and |-n03gxxxx| 3gxxx.x - n/g==xJ Finally, in concluding this thesis a summary of the quadratic electro-optic and electrostrictive results determined by the interferometric and polarimetric techniques is given and comparison of these results is drawn with those published previously. Considered briefly are some further conclusions that may be derived from these values for the nature of the electro-optic effect in KDP, ADP, and DKDP. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1999.

The dissolving pulps used in this thesis are high-grade cellulose pulps, with low amounts of hemicellulose, degraded cellulose and lignin, produced by acid bi-sulphite pulping of a fast growing South African hardwood Eucalypt clone. Microcrystalline cellulose (MCC) grade, viscose grade and cellulose acetate grade dissolving pulp were produced using a 4 stage bleaching process. MCC, viscose and cellulose acetate are the cellulose derivatives of 91% α-cellulose, 92% α-cellulose and 96% α-cellulose respectively. The key properties of the dissolving pulp considered for cellulose derivatisation are: (1) Structure (2) Accessibility and (3) ‘Reactivity’. The ‘reactivity’ depends to a large extent on the supra-molecular structure of cellulose I. Supra-molecular structure deals with the arrangement of cellulose I molecules into cellulose fibrils which then make up the cellulose fibril aggregate. The accessibility of cellulose I depends on the surface area, as determined by the size of the cellulose fibril aggregates, that are accessible; the structure of the cellulose molecules, which will determine which hydroxyl groups are accessible; and the size and type of reagent used during derivatisation. Supra-molecular changes in cellulose fibril aggregation of cellulose I, in hardwood acid bi-sulphite pulp, during bleaching and drying were studied using Atomic Force Microscopy (AFM) and Cross-polarization/Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance Spectroscopy (CP/MAS 13C-NMR – Solid state NMR) in combination with spectral fitting. There was a marked increase in cellulose fibril aggregation (i.e. supra-molecular structure) during bleaching of hardwood acid bi-sulphite pulp using 96% α-cellulose conditions. In contrast there was no increase in cellulose fibril aggregation pulp bleached using 91% α-cellulose and 92% α-cellulose bleaching conditions. An increase in hemicellulose and degraded cellulose / short chain glucan was shown to correlate with a decrease in cellulose fibril aggregation recorded using solid state NMR. Further changes in supra-molecular structure were noticed when each of the dissolving pulp samples were dried. First time drying of hardwood acid bi-sulphite pulp samples induces a significantly different degree of irreversible cellulose fibril aggregation in the 92% α-cellulose and the 96% α-cellulose pulp samples. The irreversible increase in cellulose fibril aggregation correlates with the estimated amount of hemicellulose and degraded cellulose / short chain glucan present in the pulp. The percentage increase in cellulose fibril aggregation upon drying is as follows: 96% α-cellulose > 92% α-cellulose > 91% α-cellulose. Hemicellulose and degraded cellulose / short chain glucan are among the wet chemical properties that influence cellulose fibril aggregation and the presence in dissolving pulp samples could provide steric hindrance preventing the aggregation of fibrils. Reactivity studies were carried out on the 91% α-cellulose, 92% α-cellulose and 96% α-cellulose grades of dissolving pulp. During 91% α-cellulose reactivity studies, there was no relationship between cellulose fibril aggregation, acid hydrolysis or MCC preparation. Other possible techniques for 91% α-cellulose reactivity evaluation such as the degree of polymerization (DP) determination using AFM have been discussed. Size exclusion chromatography with multi-angle laser light scattering detection was shown as a more suitable method of estimating the reactivity of 92% α-cellulose pulp samples. 96% α-cellulose reactivity studies were carried with the aid of a model system consisting of the acetylation of high purity pulp samples viz. cotton linters cellulose and 96% α-cellulose. Results indicate that the initial reaction rate constant is proportional to the specific surface area for the two cellulose pulp samples showing that specific surface area is directly related to initial reactivity of the performed acetylation. This work has shown that it is possible to control the cellulose fibril aggregation and hence specific surface area in laboratory produced 91% α-cellulose, 92% α-cellulose and 96% α-cellulose by the method in which the pulp is dried. Thus controlling cellulose fibril aggregation can probably be one viable route for controlling the initial reactivity of dissolving pulp towards acetylation. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2009.

Systematic kinetic and thermodynamic analyses of the substitution reactions of different Pt(II) complexes with a series of bio-relevant nucleophiles have been investigated as a function of concentration and temperature, using standard stopped-flow and UV–Vis Spectrophotometric methods. For this purpose, five different systems involving squareplanar Pt(II) complexes, viz. (i) mononuclear Pt(II) complexes with tridentate nitrogendonor ligands of varying degree of π-conjugation, and (ii) polynuclear Pt(II) complexes with azine, pyridyl units separated by S, S-S and CH2CH2 spacer groups, and α,ω- alkanediamine bridging ligands were synthesised and characterised by various spectroscopic methods. All substitution reactions of the Pt(II) chlorido complexes of the type [Pt(terpy)Cl]+ were studied in the presence of 10 mM LiCl to prevent spontaneous parallel reaction due to hydrolysis or solvolysis. The substitution reactions of the coordinated water molecules in the dinuclear Pt(II) complexes by thiourea nucleophiles of varying steric hindrance were studied under acidic conditions. The concentration of the nucleophile solution was prepared in 0.1 M NaClO4, at pH 2.0 and always at least 10- fold excess to provide pseudo first-order conditions. The pKa values of the coordinated aqua ligands of the dinuclear Pt(II) complexes were determined by Spectrophotometric acid-base titrations. DFT calculations were also performed in an effort to account for the observed reactivity of homologous analogues in each series of complexes, in terms of NBO charges and energies of frontier molecular orbitals. Substitution reactions of the Mononuclear Pt(II) complexes with tridentate ligands showed reactivity of the complexes is controlled by the π–acceptor characteristics of the chelate ligands. The fused rigid pyridyl system allows electronic interaction between the platinum centre and the pyridyl ligands, because of the extended conjugated π-system. This effect is controlled by how the fused ring system around the terpy moiety is structured. The isoquinoline moiety was found to reduce the effective π-backbonding and the lability of CH3PhisoqPtCl complex compared to 1,10-phenanthroline and terpyridine systems, indicating that isoquinoline ligand is a net σ-donor. The results obtained for the substitution reactions of the diaqua Pt(II) complexes with the thiourea and ionic (Br-, I- SCN-) nucleophiles demonstrate that reactivity increases with decreasing pKa values as well as decreasing distance between the Pt(II)centres. An increase in steric crowding at the Pt(II) centre imposed by the methyl groups on the azine linker decelerates the lability of the aqua ligands. The 1H and 195Pt NMR spectroscopic results confirmed degradation of the aromatic-based bridging ligand from the metal centre. The final cleavage of the complex linkers was only achieved after addition of excessive amounts of thiourea and other strong nucleophiles. The negative activation entropies and second-order kinetics for all the substitution reactions support the Associative mode of substitution mechanism. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

Many organic compounds are chiral and they are useful because of the biological activities associated with them. The biological activities of chiral compounds are often linked to absolute configuration, i.e. a compound and its mirror image can have different biological activities. For example, one enantiomer can be toxic whereas the other enantiomer is non-toxic. Enantioselective synthesis plays a significant role in the synthesis of biologically active compounds. The activity of tetrahydroisoquinolines prompted us to investigate the stereoselective synthesis of selected 1-substituted tetrahydroisoquinolines. The objectives of this project were to investigate stereoselective synthesis of some 1- substituted tetrahydroisoquinolines and compare different chiral auxiliaries used in the Bischler-Napieralski and Pictet-Spengler reactions and finally to optimize the number of steps needed to prepare the target compounds. The main challenge encountered in the Pictet-Spengler method was the decomposition of the phenylacetaldehyde. The successfully used method was the Bischler-Napieralski reaction because it does not involve the use of a phenylacetaldehyde. Using the Bischler-Napieralski method, non-stereoselective and stereoselective syntheses of tetrahydroisoquinolines have been achieved. The racemic tetrahydroisoquinolines have been synthesized in a three-step procedure starting from 3,4-dimethoxyphenylethylamine whereas the chiral tetrahydroisoquinolines were synthesized from vanillin in a seven-step reaction procedure. The R and S enantiomers of α-methylbenzylamine were successfully employed in the synthesis of 1-benzyltetrahydroisoquinolines. However, the Renantiomer of 1,2,3,4-tetrahydro-1-naphthylamine could be used to form a chiral phenylethylamine, while ring closure in a Biscler-Napieralski reaction was not successful under similar reaction conditions. The diastereoselectivity of the reactions to form the chiral tetrahydroisoquinolines was determined using NMR spectroscopy and was found to be 96% and 90% de for the (R)- and (S)-1-benzyl-6,7-dimethoxy-N-(1-phenylethyl)-1,2,3,4-tetrahydroisoquinoline, respectively. The stereochemistry of the final products was found to be similar to that of the chiral auxiliary starting material for each of the synthesized chiral tetrahydroisoquinolines. Yields for the precursors were good to moderate, especially on the final stages of the synthesis. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2014.