Chemical and spectroscopic studies of chromone derivatives
- Ramaite, Ipfani David Isaiah
- Authors: Ramaite, Ipfani David Isaiah
- Date: 1993 , 2012-11-16
- Subjects: Heterocyclic compounds -- Derivatives -- Research , Benzopyrans -- Research , Coumarins -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4422 , http://hdl.handle.net/10962/d1006888 , Heterocyclic compounds -- Derivatives -- Research , Benzopyrans -- Research , Coumarins -- Research
- Description: A number of biologically active chromones occur in plants (eg. Khellin) and research in this field has eventually led to the discovery of chromoglycic acid, which is widely used as a sodium salt in asthma therapy. Since biological activity may be related to acidity, a range of chromone-2-carboxylic acids have been prepared via Claisen acylation of substituted o- hydroxyacetophenones and their acid dissociation constants determined potentiometrically to explore substituent effects. From this study it has been found that introduction of certain groups does have a marked effect on acidity. A variety of acrylamide derivatives have been prepared via the dimethylamine-mediated ring opening of chromone-2-carboxamides which, in turn, were prepared from the chromone-2- carboxylic acids via the corresponding acid chlorides. Variable temperature NMR spectroscopy was employed to examine the effect of substituents on the rotational barriers and it has been found that for the acrylamides examined, ring substituents have little effect on the rotational barriers. A combination of low resolution, high resolution and meta-stable peak analysis has been used to study mass fragmentation patterns for a series of acrylamide derivatives. The proposed fragmentation pathways for selected peaks have been found to be common to all the spectra examined when differences in the atomic masses of substituents were taken into account.
- Full Text:
- Date Issued: 1993
- Authors: Ramaite, Ipfani David Isaiah
- Date: 1993 , 2012-11-16
- Subjects: Heterocyclic compounds -- Derivatives -- Research , Benzopyrans -- Research , Coumarins -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4422 , http://hdl.handle.net/10962/d1006888 , Heterocyclic compounds -- Derivatives -- Research , Benzopyrans -- Research , Coumarins -- Research
- Description: A number of biologically active chromones occur in plants (eg. Khellin) and research in this field has eventually led to the discovery of chromoglycic acid, which is widely used as a sodium salt in asthma therapy. Since biological activity may be related to acidity, a range of chromone-2-carboxylic acids have been prepared via Claisen acylation of substituted o- hydroxyacetophenones and their acid dissociation constants determined potentiometrically to explore substituent effects. From this study it has been found that introduction of certain groups does have a marked effect on acidity. A variety of acrylamide derivatives have been prepared via the dimethylamine-mediated ring opening of chromone-2-carboxamides which, in turn, were prepared from the chromone-2- carboxylic acids via the corresponding acid chlorides. Variable temperature NMR spectroscopy was employed to examine the effect of substituents on the rotational barriers and it has been found that for the acrylamides examined, ring substituents have little effect on the rotational barriers. A combination of low resolution, high resolution and meta-stable peak analysis has been used to study mass fragmentation patterns for a series of acrylamide derivatives. The proposed fragmentation pathways for selected peaks have been found to be common to all the spectra examined when differences in the atomic masses of substituents were taken into account.
- Full Text:
- Date Issued: 1993
Innovations in gold extraction
- Authors: Davidson, Raymond John
- Date: 1993
- Subjects: Gold -- Analysis -- Research Gold -- Metallurgy -- Research Gold mines and mining -- Research
- Language: English
- Type: Thesis , Doctoral , DSc
- Identifier: vital:4317 , http://hdl.handle.net/10962/d1004975
- Description: The thesis takes the form of a collection of publications and patents concerning gold extraction which were presented over a period of 18 years while employed at the Anglo American Research Laboratories.
- Full Text:
- Date Issued: 1993
- Authors: Davidson, Raymond John
- Date: 1993
- Subjects: Gold -- Analysis -- Research Gold -- Metallurgy -- Research Gold mines and mining -- Research
- Language: English
- Type: Thesis , Doctoral , DSc
- Identifier: vital:4317 , http://hdl.handle.net/10962/d1004975
- Description: The thesis takes the form of a collection of publications and patents concerning gold extraction which were presented over a period of 18 years while employed at the Anglo American Research Laboratories.
- Full Text:
- Date Issued: 1993
The thermodynamics of solutions and binary liquid mixtures
- Authors: Mercer-Chalmers, June Dawn
- Date: 1993
- Subjects: Thermodynamics Liquids Solution (Chemistry)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4390 , http://hdl.handle.net/10962/d1005055
- Description: The thesis is presented in two parts. In part one, the excess thermodynamic properties have been determined for several binary liquid mixtures, with the aim of testing theories of liquid mixtures. The excess molar enthalpies, Hem, have been determined using an LKB flow microcalorimeter, and the excess molar volumes, Vem, have been determined using an Anton Paar densitometer. The HemS and VemS have been measured at 298.15 K for binary systems involving an alkanol (methanol, ethanol, I-propanol, 2-propanol) mixed with a hydrocarbon (l-hexene, I-heptene, l-octene, I-hexyne, I-heptyne, l-octyne, toluene, mesitylene, 0-, m-, or p-xylene, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclodecane). The results show trends relating to the degree of unsaturation, or size, of component molecules as well as the position of the hydroxyl group on the alkanol. Measurements were also made on mixtures involving an (n-alkane + a pseudo-n-alkane) and ( a cYcloalkane + a pseudo-cycloalkane). Two theories of liquid mixtures were tested in this work. The first theory tested was the theory of Congruency. This theory was tested, by means of a null test, on a novel set of mixtures involving an n-alkane (hexane, heptane, octane, decane, dodecane) + a pseudo-nalkane,and mixtures of a cycloalkane (cyclopentane, cyclohexane, cycloheptane, cyclooctane)+ a pseudo-cycloalkane. Deviations from the theory was less than the experimental error for the (n-alkane + pseudo-n-alkane) mixtures. However, significant deviations were observed for the mixtures of (a cycloalkane + a pseudo-cycloalkane). The second theory tested was the Flory theory, which has been used to predict the excess molar enthalpies and excess molar volumes for the mixtures involving (a 1-alkene, or 1-alkyne, or methyl-substituted benzene) + an alkanol. The results show that the theory does not hold for hydrocarbon mixtures involving an alkanol. In the second part of this thesis, the partial molar volumes, at infinite dilution, of binary solution involving a solid solute (18-crown-6 ether, dibenzo-18-crown-6 ether, dicyclohexanov 18-crown-6 ether, 15-crown-5 ether, or cryptand-222) are determined in various solvents. The results were repeated with a view to determine the volume changes at infinite dilution upon complexation, ΔV∞ of the crown ether or cryptand with a metal halide salt, MX (NaCl, NaI, KCl, KI, CsCl, CsI). The ΔV∞ results were compared with results in the literature for cryptand-222 (c-222) and dibenzo-18-crown-6 ether (B₂CE6) complexed with MX, and the study was extended to include further MX complexes with c-222 and B₂CE6, as well as MX complexes with 15-crown-5 ether and dicyclohexano-18-crown-6 ether. ΔV∞ results were correlated with the Hepler prediction of the electrostriction solvent effect.
- Full Text:
- Date Issued: 1993
- Authors: Mercer-Chalmers, June Dawn
- Date: 1993
- Subjects: Thermodynamics Liquids Solution (Chemistry)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4390 , http://hdl.handle.net/10962/d1005055
- Description: The thesis is presented in two parts. In part one, the excess thermodynamic properties have been determined for several binary liquid mixtures, with the aim of testing theories of liquid mixtures. The excess molar enthalpies, Hem, have been determined using an LKB flow microcalorimeter, and the excess molar volumes, Vem, have been determined using an Anton Paar densitometer. The HemS and VemS have been measured at 298.15 K for binary systems involving an alkanol (methanol, ethanol, I-propanol, 2-propanol) mixed with a hydrocarbon (l-hexene, I-heptene, l-octene, I-hexyne, I-heptyne, l-octyne, toluene, mesitylene, 0-, m-, or p-xylene, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclodecane). The results show trends relating to the degree of unsaturation, or size, of component molecules as well as the position of the hydroxyl group on the alkanol. Measurements were also made on mixtures involving an (n-alkane + a pseudo-n-alkane) and ( a cYcloalkane + a pseudo-cycloalkane). Two theories of liquid mixtures were tested in this work. The first theory tested was the theory of Congruency. This theory was tested, by means of a null test, on a novel set of mixtures involving an n-alkane (hexane, heptane, octane, decane, dodecane) + a pseudo-nalkane,and mixtures of a cycloalkane (cyclopentane, cyclohexane, cycloheptane, cyclooctane)+ a pseudo-cycloalkane. Deviations from the theory was less than the experimental error for the (n-alkane + pseudo-n-alkane) mixtures. However, significant deviations were observed for the mixtures of (a cycloalkane + a pseudo-cycloalkane). The second theory tested was the Flory theory, which has been used to predict the excess molar enthalpies and excess molar volumes for the mixtures involving (a 1-alkene, or 1-alkyne, or methyl-substituted benzene) + an alkanol. The results show that the theory does not hold for hydrocarbon mixtures involving an alkanol. In the second part of this thesis, the partial molar volumes, at infinite dilution, of binary solution involving a solid solute (18-crown-6 ether, dibenzo-18-crown-6 ether, dicyclohexanov 18-crown-6 ether, 15-crown-5 ether, or cryptand-222) are determined in various solvents. The results were repeated with a view to determine the volume changes at infinite dilution upon complexation, ΔV∞ of the crown ether or cryptand with a metal halide salt, MX (NaCl, NaI, KCl, KI, CsCl, CsI). The ΔV∞ results were compared with results in the literature for cryptand-222 (c-222) and dibenzo-18-crown-6 ether (B₂CE6) complexed with MX, and the study was extended to include further MX complexes with c-222 and B₂CE6, as well as MX complexes with 15-crown-5 ether and dicyclohexano-18-crown-6 ether. ΔV∞ results were correlated with the Hepler prediction of the electrostriction solvent effect.
- Full Text:
- Date Issued: 1993
Thermal decomposition of mixed metal oxalates
- Authors: Coetzee, Anita
- Date: 1993
- Subjects: Oxalates -- Research , Decomposition (Chemistry)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4388 , http://hdl.handle.net/10962/d1005053 , Oxalates -- Research , Decomposition (Chemistry)
- Description: The mixed metal oxalates, FeCu(ox)₂.3H₂0, CoCu(ox)₂.3H₂0, and NiCu(ox)₂.3.5H₂0, [ox = C₂0₄] have been prepared by coprecipitation from solution. The thermal behaviour of these compounds in nitrogen and in oxygen has been examined using thermogravimetry (TG), thermomagnetometry (TM), differential scanning calorimetry (DSC) and evolved gas analysis (EGA), and results are compared with results obtained for Cuox and Mox.yH₂0. The thermal behaviour of the mixed oxalates, MCU(OX)₂.xH₂0, differed from that of the individual metal oxalates, Cuox, Coox.2H₂0, Niox.2H₂0 and Feox.2H₂0. All three mixed oxalates on heating in N₂, first dehydrate and then decompose in at least two overlapping endothermic stages. Both CO and CO₂ were evolved in proportions which varied with the surrounding atmosphere, and from compound to compound, and with extent of reaction of a given compound. The mixed oxalates, MCU(OX)₂.xH₂0, do not show the exothermic behaviour characteristic of Cuox, and reasons for this are discussed. Thermochemical calculations were done and the enthalpies of formation of the hydrates and dehydrated oxalates were determined. It was found that the enthalpy of mixing was very small or within experimental error. X-ray powder diffraction patterns for the individual and mixed oxalates were compared. The pattern for Cuox differs from the patterns obtained for the other oxalates, confirming suggestions that Cuox has a structure different to most other transition metal oxalates. The kinetics of dehydration and decomposition of the mixed oxalates were investigated, using isothermal and programmed temperature TG and DSC experiments. The yield and composition of evolved gases during isothermal decomposition were measured and compared with the enthalpy changes. X-ray photoelectron spectroscopy studies provided some information on the electron environment of the metal atoms in the various oxalates.
- Full Text:
- Date Issued: 1993
- Authors: Coetzee, Anita
- Date: 1993
- Subjects: Oxalates -- Research , Decomposition (Chemistry)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4388 , http://hdl.handle.net/10962/d1005053 , Oxalates -- Research , Decomposition (Chemistry)
- Description: The mixed metal oxalates, FeCu(ox)₂.3H₂0, CoCu(ox)₂.3H₂0, and NiCu(ox)₂.3.5H₂0, [ox = C₂0₄] have been prepared by coprecipitation from solution. The thermal behaviour of these compounds in nitrogen and in oxygen has been examined using thermogravimetry (TG), thermomagnetometry (TM), differential scanning calorimetry (DSC) and evolved gas analysis (EGA), and results are compared with results obtained for Cuox and Mox.yH₂0. The thermal behaviour of the mixed oxalates, MCU(OX)₂.xH₂0, differed from that of the individual metal oxalates, Cuox, Coox.2H₂0, Niox.2H₂0 and Feox.2H₂0. All three mixed oxalates on heating in N₂, first dehydrate and then decompose in at least two overlapping endothermic stages. Both CO and CO₂ were evolved in proportions which varied with the surrounding atmosphere, and from compound to compound, and with extent of reaction of a given compound. The mixed oxalates, MCU(OX)₂.xH₂0, do not show the exothermic behaviour characteristic of Cuox, and reasons for this are discussed. Thermochemical calculations were done and the enthalpies of formation of the hydrates and dehydrated oxalates were determined. It was found that the enthalpy of mixing was very small or within experimental error. X-ray powder diffraction patterns for the individual and mixed oxalates were compared. The pattern for Cuox differs from the patterns obtained for the other oxalates, confirming suggestions that Cuox has a structure different to most other transition metal oxalates. The kinetics of dehydration and decomposition of the mixed oxalates were investigated, using isothermal and programmed temperature TG and DSC experiments. The yield and composition of evolved gases during isothermal decomposition were measured and compared with the enthalpy changes. X-ray photoelectron spectroscopy studies provided some information on the electron environment of the metal atoms in the various oxalates.
- Full Text:
- Date Issued: 1993
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