Alkane oxidation using metallophthalocyanine as homogeneous catalysts
- Authors: Grootboom, Natasha Denise
- Date: 2002
- Subjects: Oxidation , Alkanes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4449 , http://hdl.handle.net/10962/d1007794
- Description: Iron polychlorophthalocyanine (FePc(Cl)₁₆) and tetrasulfophthalocyanine ([M¹¹TSPc]⁴) complexes of iron, cobalt and manganese are employed as catalysts for the oxidation of cyclohexane using tert-butyl hydroperoxide (TBHP), chloroperoxybenzoic acid (CPBA) and hydrogen peroxide as oxidants. Catalysis using the FePc(Cl)₁₆ was performed in a dimethylformamide:dichloromethane (3 :7) solvent mixture. For the [Fe¹¹TSPc]⁴⁻, [Co¹¹TSPc]⁻ and [Mn¹¹TSPc]⁴⁻catalysts, a water:methanol (1:9) mixture was employed. The products of the catalysis are cyclohexanone, cyclohexanol and cyclohexanediol. The relative percentage yields, percentage selectivity and overall percentage conversion of the products depended on types of oxidant, or catalyst, concentrations of substrate or catalysts and temperature. TBHP was found to be the best oxidant since minimal destruction of the catalyst and higher selectivity in the products were observed when this oxidant was employed. Of the four catalysts investigated [Fe¹¹TSPc]⁴⁻ yielded the highest overall percentage conversion of 20%.The mechanism of the oxidation of cyclohexane in the presence of the FePc(Cl)₁₆ and [M¹¹TSPc]⁴⁻ involves the oxidation of these catalysts, forming an Fe(IlI) phthalocyanine species as an intermediate. Electrocatalysis using [Co¹¹TSPc]⁴⁻ as catalyst, employed an aqueous pH 7 buffer medium for electro-oxidation of 4-pentenoic acid. An enone is suggested as the only oxidation product of 4-pentenoic acid. No degradation of [Co¹¹TSPc]⁴⁻ was observed during the electrocatalytic process. In this process water was used as a source of oxygen therefore eliminating the production of by products from oxidant as in the case of TBHP and CPBA. This system was studied In an attempt to set up conditions for alkane electrocatalytic oxidation.
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- Date Issued: 2002
Development of nickel-selective molecularly imprinted polymers
- Authors: Tshikhudo, Tshinyadzo Robert
- Date: 2002 , 2013-07-25
- Subjects: Imprinted polymers , Imprinted polymers -- Synthesis , Molecular imprinting , Nickel , Nickel -- Metallurgy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4292 , http://hdl.handle.net/10962/d1004449 , Imprinted polymers , Imprinted polymers -- Synthesis , Molecular imprinting , Nickel , Nickel -- Metallurgy
- Description: A series of eight novel bidentate ligands, designed for use in the construction of nickel-selective molecularly imprinted polymers (MIP's), have been prepared. The synthetic pathway was established by retrosynthetic analysis of the target molecules to the readily available precursors, pyridine-2-carbaldehyde (or 6-methylpyridine-2-carbaldehyde) and ethyl bromoacetate. The ligands were designed to contain an allyl group for co-polymerisation and amine and pyridyl nitrogen donors, located to permit the formation of 5-membered nickel chelates. The eight novel ligands and their respective precursors were characterized by elemental (high-resolution MS) and spectroscopic (IR and ¹H and ¹³C NMR) analysis. High resolution electron-impact mass spectrometry has also been used, together with B/E linked scan data, to explore the fragmentation patterns of selected ligands. The various nickel(ll) complexes were analyzed using spectroscopic techniques and, in some cases, elemental analysis; computer modelling has also been used to explore conformational effects and complex stability. Numerous MIP's, containing nickel(II) complexes of the bidentate ligands, have been prepared, using ethylene glycol dimethylacrylate (EGDMA) as the cross-linker, azobis(isobutyronitrile) (AlBN) as the polymerization initiator and MeOH as the porogenic solvent. The template nickel(II) ions were leached out with conc. HCI, and the nickel(II) selectivity [in the presence of Fe(Ill)] of the nickel-imprinted polymers was examined by ICP-MS analysis. The ICP-MS data indicate that the MIP's examined exhibit extremely high selectivity for nickel over iron. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
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- Date Issued: 2002
Synthetic approaches to marine labdane diterpenes
- Authors: Wisch, Gregory Albert
- Date: 2002 , 2013-05-10
- Subjects: Diterpenes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4289 , http://hdl.handle.net/10962/d1003131 , Diterpenes
- Description: The work presented in this thesis describes the synthesis of labd-13-en-8ß, 15-diol (46) a stable reduced derivative of an unstable marine natural product aldehyde [8ß-hydroxylabd-13E-en-15-al (6)] isolated by Cimino, et al. from the skin of a Notaspidean mollusc Pleurobranchaea meckelii. The rationale for the synthesis was to provide sufficient 46 for eventual mild oxidation to 6 and investigation of the biological activity of this latter compound. (-)-Sclareol (32), a common diterpene synthetic precursor, was the starting point for the ten step synthesis of 46 described in this thesis. A search of the literature revealed that only one non stereospecific synthesis of 46 had been previously reported. To provide the necessary background to the synthetic component of this thesis, both the occurrence of labdane and ent-labdane in the marine environment and the use of sclareol in the synthesis of marine natural products, was reviewed. The initial step in the synthesis of 46 was the potassium permanganate oxidation of sclareol to give a bisnorlabdane ketone. Reduction of this ketone with lithium aluminium hydride produced a mixture of diols which, through t-butyldimethysilyl triflate protection, afforded a quantitative route to protecting the C-13 ketone in an effort to prevent unwanted intramolecular cyclization reactions. Dehydration of the tertiary alcohol moiety at C-8 with phosphorous oxychloride yielded the Δ⁸·¹⁵ exocyclic alkene required for the next oxidation step. Ozonolysis succeeded in producing the desired C-8 ketone after much deliberation and research into alternative oxidation strategies. Methyl lithium methylation quantitatively afforded the desired a-methyl substitution at C-8, identified at the onset as the key step in the synthesis. Tetra-butylarnmonium fluoride deprotection yielded the 8ß,13-dihydoxylated product, which was in turn subjected to a Swern oxidition to give the desired 8ß-hydroxy-bisnorlabda-13-one. A modified Horner-Wadsworth-Emmons reaction allowed for elaboration at C-13 to yield a to Δ¹³ olefin with a terminal C-15 ethyl ester. Diisobutylaluminium hydride reduction of the ester produced the desired labd-13-en-8ß, 15-diol (46) in a low overall yield of 3.4%. Although opportunities for optimization of at least three steps in the synthesis exist, time constraints prevented both optimization of these steps and an investigation of the oxidation of 46 to 6. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
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- Date Issued: 2002
Thermal and photostability studies of furosemide and its cyclodextrin mixtures
- Authors: Melane, Babalwa Blossom
- Date: 2002 , 2013-05-16
- Subjects: Furosemide , Furosemide -- Stability
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4440 , http://hdl.handle.net/10962/d1007625 , Furosemide , Furosemide -- Stability
- Description: Furosemide (Lasix®), abbreviated as FR and also known as frusemide, is a drug used for renal problems and treatment of cardiac edema. Various polymorphic forms of furosemide, dependent upon the method of preparation and thermal treatment, have been reported. The main thermal decomposition product of furosemide has been identified as saluamine. The dissolution properties of furosemide have also been reported to be improved by complexation with beta-cyclodextrin. Photostabilities of the different crystal forms have been studied. Differential scanning calorimetry (DSC) and thermogravimetry (TG) have been used to examine the thermal behaviour of furosemide itself and of its physical and kneaded mixtures with betacyclodextrin (BCD) and gamma-cyclodextrin (GCD). There is strong evidence from DSC that complex formation between FR and GCD occurs. This is supported by IR and XRD data. Decreases in the intensity and broadening of the characteristic carbonyl (1660 cm'l) and amine (1588 cm⁻¹) bands in the kneaded mixture, compared to the physical mixture, were observed with IR. X-ray diffraction results for the 1:3 molar ratio FR/GCD kneaded mixture showed a halo diffraction pattern characteristic. of an amorphous solid and did not resemble patterns from the drug, or the gamma, cyclodextrin, or the physical mixture. Photostability studies have been conducted on solid furosemide and its mixtures with GCD or BCD. An HPLC method was developed to determine the amount of drug remaining after exposure and the presence of any degradants. Results indicated that about 10% degradation of the drug occurred during exposure for 16 hours at 550 W/m², with the appearance of polar degradants. Although IR and DSC results for the 1:3 molar ratio FR/GCD kneaded mixture showed a probable strong interaction between FR and GCD, the photostability of FR was decreased. The 1 :3 molar ratio FR/BCD kneaded mixture showed less photo-degradation than the 1:3 molar ratio FR/GCD mixture under similar conditions, suggesting that inclusion of the drug molecule (FR) is different in the two cyclodextrins.
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- Date Issued: 2002