Kinetic studies of a number of interesting and significant reactions involving activation of hydrogen, olefins, oxygen and carbon monoxide by solutions of rhodium complexes containing sulphur and/or chloride ligands are described. The cis 1,2,3-trichlorotris(diethylsulphide)rhodium (III) complex, RhCl(EtS₃and the corresponding dibenzyl sulphide complex, RhCl₃(Bz₂S)₃in N,N -dimethylacetamide (DMA) solution were found to be effective catalysts for the homogeneous hydrogenation of maleic, fumaric and trans-cinnamic acids. The kinetic data are consistent with a dissociation of a sulphur ligand prior to the hydrogen reduction of rhodium (III) to rhodium (I). The rhodium (I) is stablized in solution by rapid complexing with the olefin to produce a Rh¹(olefin)(Ln) complex (L = auxiliary ligands) which then reacts with H₂ in a rate determining step to produce the saturated paraffin and rhodium (I). In some instances, more complex kinetics resulted when one of the auxiliary ligands in the Rh¹ (olefin)(Ln) complex dissociates prior to reaction with H(2); a unique apparent zero order in catalyst concentration has been observed. Isomerization was observed in the RhCl(EtS)₃catalyzed hydrogenation of fumaric acid and a mechanism involving rhodium (III) alkyl intermediate seems likely. The cyclooctene complex, [Rh(C8H14)₂C1], in DMA was found to be a convenient source for preparing rhodium (I) complexes "in situ" by adding the desired ligands, for example, chloride or diethyl sulphide. Kinetic data obtained using such solutions are in good agreement with the hydrogenation data obtained by starting from the corresponding rhodium (III) complexes. This result confirms that rhodium (I) intermediates are involved in the catalytic hydrogenation starting from rhodium (III) complexes. During studies to investigate the effect of solvent on catalytic hydrogenation of olefins by rhodium (III) complexes, dimethyl sulphoxide (DMSO) was found to be catalytically reduced by hydrogen to dimethyl sulphide and water in the presence of RhCl(EtS)₃ and RhCl‧3H2O. The kinetics were consistent with a rate determining heterolytic splitting of H₂ by Rh(III)(DMSO) to produce Rh[III](DMSO)H¯ which then decomposes to the products in a fast step. RhCl₃‧3H₂O also catalyzed the oxidation of DMSO to dimethyl sulphone using a mixture of oxygen and hydrogen. The solution of [Rh(C8H14)₂C1]₂ in DMA containing LiCl was found to be a versatile catalyst, for besides the activation of hydrogen and olefins, oxygen and carbon monoxide could also be activated. The formation of a rhodium (I) molecular oxygen complex, Rh(I)(O2) and a subsequent catalyzed oxidation of the DMA solvent and cyclooctene were studied in detail. The formation of the Rh(I)(O2) complex appears to be irreversible. An E.S.R. signal, possibly due to species such as Rh(II)(O2¯) was also observed. The kinetics of the oxidation suggest the equilibrium formation of the Rh(I)(O2) complex followed by a rate determining step to give the products. A free radical mechanism seems likely. Solutions of [Rh(C8H14)₂C1]₂ in LiCl/DMA readily reacted with carbon monoxide to form a Rh(I)(CO)₂ species. A solution of the oxygen complex was converted more slowly to the Rh(I)(CO)₂ species in a reaction whose observed rate was determined by the dissociation of the coordinated oxygen. Preliminary studies indicated that a mixture of CO and O₂ is converted catalytically to CO₂ by a solution of [Rh(C8H14)₂C1]₂ in LiCl/DMA. / Science, Faculty of / Chemistry, Department of / Graduate

Orientador: Walace Alves de Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-26T13:24:33Z (GMT). No. of bitstreams: 1 Lima_JoaquimMatiasBittencourt_M.pdf: 2410483 bytes, checksum: eb7f40c8e6feac1eec3059a9a6ccfb12 (MD5) Previous issue date: 1979 / Resumo: Foi desenvolvido o estudo de um padrão ebuliométrico para solventes não aquosos. Benzila foi escolhido como soluto e benzeno como padrão. Foram medidas as elevações na temperatura de ebulição do benzeno, causadas pela adição de benzila, e os coeficientes osmótico e de atividade puderam ser avaliados. A aparelhagem e o método operacional são descritos. São discutidos os diversos tipos de sensores de temperatura que podem ser utilizados e apresentadas as razões pelas quais foram escolhidos termístores para tal fim. Os termistores foram calibrados, e com base em calibração anterior, foram avaliadas as alterações nas suas características. São propostas equações para que, por método analítico, sejam medidas as elevações de temperatura, o coeficiente de atividade e o coeficiente osmótico. Foi discutido o desvio da idealidade apresentado pelo padrão. É proposto um método comparativo para determinação de constante de equilíbrio, permitindo com que, utilizando o padrão ebuliométrico, fosse determinada a constante de dimerização do ácido benzóico em benzeno, cujo resultado, comparado com dados oriundos da literatura, apresentou boa concordância / Abstract: The behavior of benzil as an ebulliometric standard for non-aqueous solvents was studied. Boiling-temperature elevations due to addition of benzil in benzene were measured and osmotic and activity coefficients were calculated. The apparatus and procedure are discussed. Several types of temperature sensors are mentioned and thermistors were chosen to be used. The thermistors were calibrated and the changes in their parameters were evaluated based on results of previous calibration. Equations are given which permit the calculation of boiling-temperature elevation of benzene solutions as well as osmotic and activity coefficients. The departure from ideal behavior is discussed. A comparative method for the ebulliometric determination of equilibrium constants is proposed. The dimerization constant of benzoic acid in benzene was determined by this method and the results are in good agreement with literature values / Mestrado / Quimica Organica / Mestre em Química

Inkjet printing (jetting) technology, due to its high speed of operation and accuracy, is utilised in Additive Manufacturing (AM) of three dimensional parts. Commercially available AM processes that use jetting technology include three dimensional printing (3DP by Z-Corporation), Polyjet (by Objet), Multi Jet Modelling (MJM by 3D Systems) and three dimensional printing by Solidscape. Apart from 3D Printing by Z-corporation, all the other jetting based processes require a support material to successfully build a part. The support material provides a base to facilitate the removal of the part from the build platform and it helps manufacturing of cavities, holes and overhanging features. These support materials present challenges in terms of their removability and reusability. This research is therefore, aimed towards finding a support material composition that can be used with jetting based AM processes. The support material should be easily removable either by melting or by dissolution and also, if possible, it should be reusable. AM processes often process materials with poor mechanical properties and therefore, the parts produced by these processes have limited functionality. In an attempt to obtain complex shaped, functional parts made of nylon (i.e. Polyamide 6), a new jetting based AM process is under research at Loughborough University. The process uses two different mixtures of caprolactam (i.e. the monomer used to produce polyamide). These mixtures are to be jetted using inkjet heads and subsequently polymerised into polyamide 6. Therefore, another aim of this research was to consider the support material s suitability for jetting of caprolactam. Two different polymers were researched which included Pluronic F-127 and methylcellulose (MC). Both these polymers are known for gel formation upon heating in aqueous solutions. Due to the inhibition of polymerisation of polyamide 6 by the presence of water, non-aqueous solvents such as ethylene glycol, propylene glycol and butylene glycol were studied. Since both F-127 and MC in the glycols mentioned above had not been studied before, all the compositions prepared and investigated in this report were novel. F-127 did not show gel formation in propylene and butylene glycol but formed a gel in ethylene glycol at a concentration of 25% (w/w) F-127. MC, on the other hand, showed gel formation upon cooling in all the three glycols at concentrations as low as 5% for ethylene glycol and 1% for both propylene and butylene glycol. These compositions were characterized using experimental techniques such as Fourier Transform Infrared (FTIR) spectroscopy, hot stage microscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD). A mechanism of gelation for both F-127 and MC in glycols is presented based on the results of these characterisation techniques. Viscosity and surface tension measurements along with the texture analysis of selected compositions were also performed to evaluate their suitability for jetting. All these compositions, due to their water solubility and/or low melting temperatures (i.e. near 500C) present the advantage of ease of removal. Removal by melting at low temperatures can also provide reusability of these support materials and thus advantages such as reduction in build cost and environmental effect can be achieved.

The electrochemical oxidation of CoCl2(PPh3)2 was investigated in a mixture of acetonitrile and pentanol (1:1) at a platinum disk working electrode using Cyclic Voltammetry (CV) and Chronoamperometry. Elemental Analysis and Infrared Spectroscopy were used to characterise the synthesized compounds i.e. CoCl2(PPh3)2 and CoCl(PPh3)3. Cyclic Voltammetry was utilised for the examination of different working electrode materials that could be used for the anodic voltammetric studies of CoCl2 (PPh3)2, to characterise the reactants and products of each electrode reaction, to investigate the chloride binding ability to a CoCl(PPh3)3 complex, and to evaluate the electrocatalytic substitution of chloride by PPh3 from the complex CoCl2(PPh3)2. Use of ferrocene as an internal standard during the anodic studies of CoCl2(PPh3)2 was also evaluated. The number of electron involved in the electrode process, CoII to CoIII from CoCl2(PPh3)2 and diffusion coefficient of ferrocene in a mixture of acetonitrile and pentanol (1:1) were determined using Chronoamperometry. Ultraviolet-Visible (UV-Vis) and 31P Nuclear Magnetic Resonance (31P NMR) spectra were used to assist with the characterisation of the electrode reactions involved during oxidation of CoCl2(PPh3)2. / Dissertation (MSc (Chemistry))--University of Pretoria, 2008. / Chemistry / unrestricted