The mechanism of permanganate oxidation of fluoral hydrate and its analogue, substituted with deuterium at position-1, has been extensively investigated throughout the pH region 0.7 to 14 and a successful study was made of the behaviour of permanganate in the sulfuric acid region from pH 0.7 to 46.3% H₂SO₄. Compared with 2,2,2-trifluoroethanol and other substituted ethanols which ionise in the pH region, fluoral hydrate is unique since it has two acidic hydrogens, both of which can ionise. The pK[subscript a] for the first ionisation process has been determined to be 10.1. From the kinetic data as well as other supporting evidence, at least four different reaction paths can be distinguished for the permanganate oxidation of fluoral hydrate: (i) Reaction of the di-anion of fluoral hydrate, (ii) Reaction of the mono-anion, (iii) Reaction of the unionised fluoral hydrate with permanganate anion, and (iv) Tentatively proposed reaction of the unionised fluoral hydrate with permanganic acid. The deuterium isotope effects range from k[subscript H]/k[subscript D] = 5 for the oxidation of the di-anion, k[subscript H]/k[subscript D] = 10 for the mono-anion reaction, k[subscript H]/k[subscript D] = 4 for the neutral molecule reaction and k[subscript H]/k[subscript D] = 6 for the permanganic acid oxidation of unionised fluoral hydrate in strong acid. Activation parameters and a positive salt effect show that the transition state formation involves a reaction of similarly charged species; proton tunneling is considered unlikely on the basis of a temperature study. The rate determining step is most consistent with a hydride ion transfer to the permanganate ion. In connexion with the above study, 2,2,2-trifluoroethanol, 1,1,1;3,3,3-hexafluoropropanol-2 and the corresponding 2-d analogue have been examined in somewhat lesser detail. An isotope effect k[subscript H]/k[subscript D] = 20 has been observed for the oxidation of 1,1,1;3,3,3-hexafluoropropanol-2. The pK[subscript a] of permanganic acid has been determined in sulfuric acid by a spectrophotometry method, using two different methods of calculation; pK[subscript a] = -5.1. Formic acid has been oxidised by permanganate in the region 25 to 72 % H₂SO₄ and the reaction in the region from 25 to about 40 % H₂SO₄ is interpreted as the oxidation of the unionised formic acid by permanganic acid. An isotope effect of about 7 is observed in the very strongly acidic region (72 % H₂SO₄), which decreases upon going to 25 % H₂SO₄. Certain 4,4'-disubstituted benzhydrols were oxidised by permanganate in 0.1 M sodium hydroxide, however solubility difficulties prevented any extensive studies. [ ... ] / Science, Faculty of / Chemistry, Department of / Graduate

In order to elucidate the mechanism of hydrogen sulphide oxidation, the photo-oxidation and thermal oxidation of hydrogen sulphide were studied, using gas chromatography for the analysis of final products. Photo-oxidation was studied at 130° and 150°C. Products found were sulphur dioxide, hydrogen, water and sulphur. Production of sulphur dioxide was found to be inhibited by an increase in surface area. Whether in photo- or thermal oxidation, the yield of sulphur dioxide increased drastically with slight increases in (O₂)/H₂S) ratio. This was also observed in the yield of hydrogen in photo-oxidation. Thermal oxidation was studied at 160°, 170°, 190°, 210°, 225°, 240°, and 260°C. Products were sulphur dioxide, water, and sulphur. No hydrogen was found. An expression for the production of sulphur dioxide was obtained: [formula omitted] = k (H₂S)⁻¹→⁺¹ (O₂)³ The overall activation energy was found to be 21.2±2k.cal./mole. Comparison with previously reported works was made and a mechanism proposed. / Science, Faculty of / Chemistry, Department of / Graduate

The mechanisms of permanganate oxidation of two very different substrates have been examined. Firstly, in an attempt to elucidate the mechanism of permanganate oxidation of alcohols, a number of meta and para substituted 2,2,2-trifluoro-1-phenylethanols have been prepared and the kinetics of permanganate oxidation studied over a pH range of 1 to 13.3. Secondly, the reaction between permanganate and cyanide ion has been examined over the pH range 3 to 14.6. The reaction between permanganate and 2,2,2-trifluoro-1-phenylethanol in aqueous alkaline solution was shown to give manganate and trifluoroacetophenone (hydrated form) in almost quantitative yield under kinetic conditions and is therefore represented by the equation, 2MnO⁻₄ + C₆H₅CHOHCF₃ + 20H⁻→ 2Mn0⁼₄ + C₆H₅COCF₃ + 2H₂0 The trifluorophenylethanols are more acidic than the normal hydrogen containing secondary alcohols and their pKas as determined spectrophotometrically showed the following order of decreasing acidity for substitution into the phenyl ring m-NO₂> m-Br > H > p-CH₃ >p-MeO. The rate of reduction of permanganate was followed iodometrically and the rate expression which fits the kinetic data for the alkaline catalyzed oxidation is the following: [formula omitted]. The rate of oxidation of the p-CH₃, m-Br and unsubstituted trifluorophenylethanols-l-d by permanganate was found in each case to be 16 times slower than the rate of oxidation of the corresponding protio compounds in alkaline solution. This latter result, the kinetics, i.e., the close similarity between the ionization type rate curves and the calculated ionization curves for the alcohols, the thermodynamics and positive salt effect indicate a mechanism which involves a primary ionization step to give the anion of the alcohol and then a rate controlling bimolecular step where permanganate abstracts a hydride ion from the anion. This mechanism is somewhat invalidated in view of the observation that the rate constants obtained for oxidation of the various substituted alcohols in alkaline solution are relatively insensitive to nuclear substitution. A plot of Hammett σ values versus the log of the rate constants appears to give a smooth curve. A number of mechanisms involving termolecular steps are considered to account for this latter observation and the large deuterium isotope effect is discussed in the light of present theories. Kinetic and oxygen¹⁸ tracer experiments have been performed in an attempt to elucidate the mechanism(s) of permanganate oxidation of cyanide. A mechanistic interpretation is attempted using the data obtained in basic solution above pH 12 to 14.6 where the oxidation is represented by the equation, 2MnO₄⁻ + CN⁻ + 20H⁻→ 2MnO₄⁼ + NCO⁻ + H₂0 From pH 12 to 6 the reaction was found to be complex and unstoichiometric yielding cyanate, carbon dioxide, cyanide ion and finally cyanogen at pH 9 to 6. The rate of reduction of permanganate as followed iodometrically and spectrophotometrically, is found to be markedly dependent on the pH of the medium and reactant concentration. The observation that the rate is negligible in acid solution but rapid in basic media suggests cyanide ion and not hydrocyanic acid molecule to be the primary reactive species. At pH greater than 12 two parallel processes are indicated which have been designated as Reaction A and Reaction B. Reaction A appears at low reactant concentrations < 0.0004 M cyanide and higher hydroxyl ion concentrations > pH 13. The rate of Reaction A is represented by the kinetic expression [formula omitted] where k₂ is independent of hydroxyl ion concentration and is insensitive to the effect of manganate and barium ions. A positive salt effect is observed and labeling experiments using permanganate enriched in oxygen¹⁸ showed that the oxygen introduced into the product cyanate comes mainly from the oxidant (70%-80% oxygen transferred). These observations suggest a mechanism which involves a rate determining bimolecular reaction between permanganate and cyanide ions to yield a Mn V species and cyanate ion. The possibility that a second parallel process Reaction B was occurring was indicated by the changing kinetics at higher reactant concentrations and lower basicities, by the non-linear Arrhenius plots and the observation that only 15%-25% oxygen¹⁸ transfer from permanganate to substrate had occurred at pH 13. The rate of this latter process can be tentatively represented by the kinetic expression [formula omitted]. A mode of oxidation is suggested which appears to fit these results. Permanganate, cyanide ion and a hydrocyanic acid molecule are reacted to produce a reactive species which undergoes further oxidation by permanganate to yield cyanogen. Cyanogen hydrolysis results in cyanate where oxygen is derived from the solvent. / Science, Faculty of / Chemistry, Department of / Graduate

Pseudomonas aeruginosa is known to dissimilate glucose by way of a pathway which does not involve phosphorylation at the hexose level. The established intermediates in this pathway are gluconate, 2-ketogIuconate, pyruvate and finally the compounds of an unconventional tricarboxylic acid cycle. The major gap in our knowledge concerns the fate of 2-ketogluconate. The enzymes responsible for the degradation of this compound have proven to be very unstable and previous attempts to obtain an active cell preparation or cell free extract have met with little success. There is some evidence that drying cells in an atmosphere of carbon monoxide preserves the enzyme in question while interfering with the complete oxidation of 2-ketogluconate. This should result in the accumulation of an intermediate product and thus would make possible the elucidation of one more step in the sequence of reactions. For this reason the work on monoxide-dried cells was continued in the hope, that they would serve as a source of the 2-ketogluconate enzyme. This technique produced a preparation with a good ability to oxidize 2-ketogluconate. However, the viscous nature of the preparation made centrifugal separation of the remaining live cells almost impossible. Glucose and gluconate grown cells when suspended in a 45% solution of sucrose and subjected to sonic vibrations produced a reproducible cell free preparation with a good ability to oxidize 2-ketogluconate. This preparation had an optimum pH of 7.4 and a respiratory quotient of 3. The mechanism of this oxidation remains unexplored. Pyruvic acid was identified as a product of this reaction. The crude sucrose sonicate was not stimulated by ATP and no phosphorylation could be detected aerobically or anaerobically by measuring acid stable (ester) phosphate. The preparation was not inhibited by 2.5 x 10⁻² sodium fluoride. Moreover, a crude sonicate of gluconate grown cells in the presence of ATP and magnesium, showed no phosphorylated compounds, by the chromatographic methods employed. The study for detection of phosphorylated compounds was carried out under strict anaerobic conditions. No new intermediates were isolated in the pathway of 2-ketogluconate breakdown and this pathway still remains unknown. However, this work has provided several methods of obtaining active cell preparations. / Land and Food Systems, Faculty of / Graduate

As a significant component of lignocellulosic biomass, lignin represents a potential source of value-added aromatic chemicals. In this thesis, catalytic systems with earth-abundant metal catalysts such as molybdenum(VI) and hypervalent iodine complexes were developed to selectively break down lignin models into lower molecular weight chemicals under mild conditions. Due to the complexity of lignin, simple lignin model substrates (A to E), representing common linkages in lignin, were used to investigate the catalytic activity/selectivity of these catalysts. With the molybdenum catalysts [7– 11]/SPC/Adogen®464 system (SPC = sodium percarbonate), oxidation of simple β-1 model compound A in acetonitrile showed primarily C-H bond cleavage to form the ketone product, benzoin methyl ether, whereas the Cα-Cβ bond cleavage product, methyl benzoate, was obtained by switching the reaction solvent to benzonitrile. Preference for generating the Cα-Cβ bond cleavage product, i.e. benzaldehyde, can also be achieved with other early to middle transition metal catalysts using H2O2(aq) as the terminal oxidant. Stoichiometric amounts of hypervalent iodine/Lewis acid systems [20a-c] were able to selectively cleave Cα-Cβ bonds to aldehydes with both simple β-1 model compound A and β-O-4 model compound C. In contrast, other lignin model compounds with different linkages were unable to be oxidized to a great extent using these Mo- or iodine-based complexes. The catalytic activity and selectivity of the reported vanadium complexes, copper salts and non-metal system 1-5 on non-volatile organosolv (NVO) lignin was investigated under basic condition. Details of the depolymerisation of lignin were determined by using Gel Permeation Chromatography (GPC) and the two-dimensional NMR technique, quantitative HSQC (q-HSQC) spectroscopy. Vanadium [2] and copper systems were found to be the most active for depolymerization of NVO lignin.

Microbiological leaching of sulfide minerals in fermenters is believed to have commercial potential. The oxygen transfer rate has been assumed to be one of the most important factors affecting the leach rate. The mass-transfer rate at various solution pH's was studied by using an unsteady gassing out process. The sulfite-oxidation process was also studied in an attempt to explain the absorption mechanism. A 7.5 inch I.D. methyl methacrylate tank with 4 baffles and a 4-inch diameter paddle type impeller were used. The impeller was driven by a motor mounted on a dynamometer which allowed measurement of the power used in agitation. All the experiments were carried out under highly turbulent conditions and covered the liquid temperature range 25°C to 40°C. The results showed that pH had no effect on mass-transfer coefficient. The values of K[subscript L]a increased as temperature increased. The relationship between K[subscript L]a, power input and superficial gas velocity was found to be of the form: K[subscript L]a = c(HP/V)[superscript x] (V[subscript s])[superscript y] A comparison of the K[subscript L]a observed in an unsteady gassing out process and that in a sulfite-oxidation process showed that the interfacial area/unit volume of liquid, a, is directly proportional to (V[subscript s])º‧⁵º which coincides with Calderbank's result. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

The potential use of 6,7,8-trimethyllumazine (6,7,8-trimethyl-2,4-dioxopteridine) and Its dihydro derivative as a redox couple for the pteridine and flavin systems is investigated. The syntheses of the above compounds and related lumazine derivatives are described and their spectroscopic and chromatographic properties are tabulated. While examining the p.m.r. spectra of 6,7,8-trimethyllumazine (TML) and 7,8-dihydro-6,7,8-trimethyl-lumazine (DHTML) in deuterium oxide media, the hydrogens of the C-7 methyl group and of the C-6 methyl group in the former and latter compounds respectively were observed to undergo exchange. In the pH range -0.4 to 8.0, the exchange of TML is subject to general acid-base catalysis. The pseudo first-order exchange rate constant (k₁) was found to be the sum of several catalytic terms. Prom measurements of the exchange rate-buffer dependency at various pH values, the following values of the specific catalytic constants (in l.mole⁻¹min⁻¹) have been calculated: K[subscript H]+= 1.2, k[subscript H3PO4] = 0.41, k[subscript H2PO4]- = 0.14, k[subscript HPO4]-2 = 52.9 The mechanism of the acid- and base-catalyzed exchange of TML is outlined. The relatively facile exchange is explained in terms of the formation of neutral and ionic intermediates which have long conjugated bonding arrangements. Pseudo first-order rate constants have been tabulated for the general acid-catalyzed exchange of DHTML in the pH range -0.4 to 8.2 leading to an unusual pH-rate profile. The marked decrease in exchange rates and anomalous rate plots in the more acidic pH regions is attributed to acid-catalyzed covalent hydration across the C(6)-N(5) double bond and equilibration of hydrated and unhydrated cations. Evidence for hydration is presented and the exchange mechanism is discussed. The ferricyanide oxidation of DHTML was investigated in the pH range 5 to 12.5 by spectrophotometry and potentiometric techniques. The second-order reaction proceeds in a complicated sequence of steps, some of which are dependent upon the ionization of the reaction intermediate, trimethyl-lumazine. Beyond pH 11, the oxidation rate is directly proportional to the hydroxide ion concentration. At pH 12, the absence of a primary isotope effect and the inhibitory effect of added ferrocyanide indicate that the oxidation proceeds via an initial rapid and reversible one-electron abstraction from the anionic form of DHTML. The resulting mesoroeric radical can undergo further reactions with ferricyanide ion or with hydroxide ion. A very negative ΔS‡ value was obtained for the reaction at pH 12, consistent with a reaction between ions of the same charge. A study of the effects of potassium ion on the oxidation rate indicates the partial participation of the associated species KFe(CN)₆⁻² in the reaction. A limited study of the reaction between trimethyl-lumazine and ferricyanide was undertaken. The hydroxylated anion of TML reacts via a highly coloured intermediate to produce 7-oxo-6,8-dimethyllumazine. Further investigation into the reaction is required. / Science, Faculty of / Chemistry, Department of / Graduate

The oxidation of artificial cuprous sulphide electrodes (Cu/S ratio = 1.93) was studied in acidified copper sulphate solutions in the temperature range 20 to 35° C. Rest potential measurements gave V° = 0.490 volts for the electrode or half cell potential. This is within the limits of accuracy of V° for: Cu₂S —CuS + Cu⁺⁺ + 2e V° = 0.535 + 0.13 volts The discrepancy was thought to be related to the large Cu deficien in the sulphide. In solutions with pH>4, the rest potential measurements were consistent with the following reaction: Cu₂S + 2H₂0 —CuS + Cu(OH)₂ + 2H⁺ + 2e Polarization measurements at low overpotential gave values for the following kinetic parameters: β, the symmetry factor = 1/2 λ, the number of electrons involved in each act of the rate determining step = 2 i₀, the exchange current ≈ 2 x 10-⁵ A/cm² ΔH₀*, the standard heat of activation = 26.5 kcal/mole CuS was tentatively identified as one of the reaction products. A reaction mechanism was discussed. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The rate of oxidation of 99.99% and 99.999% pure copper samples at 1220°C by low-momentum jets of pure oxygen has been studied at gas flow rates of from 500 to 2000 cm³ min⁻¹. Oxidation rates at a given gas flow rate were found to be constant and were governed by starvation mass transfer kinetics. Factors studied for the reaction include: effect of lance height, effect of small additions of silicon and sulphur to the melt prior to oxidation, and effect of oxide patch area. Interfacial tension-generated flow, radially outward from the point of jet impingement, was observed during oxidation and surface velocity studies showed that such flow had a mean value of 26.1 ± 5.5 cm sec⁻¹ for all of the experiments and was independent of oxygen gas flow rate and copper bath oxygen concentration. Surface-blockage studies indicated that the bulk of the oxygen transfer to the copper occurred over the area described by the oxide patch. Liquid-phase oxygen mass transfer coefficients were calculated using the oxidation rates and oxide patch areas, and a mean value was found to be 0.104 ± 0.012 cm sec⁻¹ independent of oxygen flow rate, bath oxygen content, and dissolved sulphur and silicon contents. The rate of oxidation of 99.995% pure silver at 1100°C was studied using low-momentum jets of pure oxygen at flow rates of 1500 and 2000 cm³ min⁻¹ and was found not to be governed by starvation mass transfer kinetics. The oxidation rate was not dependent on oxygen gas flow rate and was found to be a factor of about 50 times less than those observed for copper. No spontaneous interfacial tension-generated flow was observed during oxidation of the molten silver and a possible explanation was postulated. Liquid-phase oxygen mass transfer coefficients were found to have a mean value of 2.88 ± .41 (10⁻³) cm sec⁻¹, independent of gas flow rate and bath oxygen content. The effect of interfacial turbulence on liquid-phase oxygen mass transfer coefficients in molten copper was to enhance the value by about 40 times over that observed in molten silver, where interfacial turbulence does not occur on oxidation. Copper deoxidation at 1220°C using low-momentum jets of pure hydrogen at flow rates of 1500 and 3000 cm³ min⁻¹ was studied, and was found not to depend on hydrogen flow rate, lance height, and starting oxygen concentration. The rate-controlling step was found to be the gas-phase mass transfer of hydrogen to the liquid surface for the first 3000 sec. of deoxidation. After this, liquid-phase oxygen mass transport control predominated. Dissolved silicon was found to retard the deoxidation rate, while dissolved sulphur was found to enhance the deoxidation rate through continued SO2 elimination. Interfacial tension-generated flow was observed during deoxidation and approximate surface velocities of 10 to 15 cm sec⁻¹ towards the point of jet impingement were observed. A mechanism for this flow was postulated. The gas-phase mass transfer coefficient was found to be 1.28 ± 0.25 cm sec⁻¹ for copper-oxygen alloys, and was 0.89 cm sec⁻¹ in the 1.28 ± 0.25 cm sec⁻¹ for copper-oxygen alloys, and was 0.89 cm sec⁻¹ in the presence of dissolved silicon and 2.68 cm sec⁻¹ in the presence of dissolved sulphur. An approximate value for the liquid-phase oxygen mass transfer coefficient in the liquid-phase control region was found to be 4.9 (10⁻³) cm sec⁻¹, and was found to be influenced by the presence of bubbling during this phase of deoxidation. The rate of deoxidation of molten silver at 1100°C by low-momentum hydrogen jets was studied at hydrogen flow rates of 1500 and 2000 cm³ min⁻¹ The rate was found not to depend upon hydrogen flow rate, but was found to decrease with decreasing starting bath oxygen concentration. Interfacial tension-generated flow was observed, during silver deoxidation, with approximate surface velocities of 10 to 15 cm sec⁻¹ towards the point of jet impingement. The rate-controlling step was found to be liquid-phase mass transfer of oxygen, and liquid-phase oxygen mass transfer coefficients were found to decrease with decreasing initial oxygen content. These values were enhanced by the presence of bubbling during deoxidation. Interfacial turbulence during the dissolution of solid CU₂S CU₂O, Se, and Te in molten copper was shown to occur. Values calculated for the spreading coefficient S, indicated that the spreading of these materials on molten copper was predictable. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The catalytic conversion of cyclohexanol to cyclohexanone using a combination of rhodium trichloride trihydrate and ferric chloride in the presence of molecular oxygen was investigated. No conversion to cyclohexanone occurred in the absence of rhodium trichloride trihydrate, but some degree of conversion was found in the absence of ferric chloride. The optimum conditions for catalytic oxidation were produced by using a combination of rhodium trichloride trihydrate and ferric chloride, and under these conditions the rate of conversion to the ketone declined steadily, until the mixture contained approximately U0% cyclohexanone. For a fixed amount of cyclohexanol and rhodium trichloride trihydrate it was found that there was an optimum amount of ferric chloride necessary to produce the maximum yield in the shortest possible time. Addition of ferric chloride in excess of this optimum amount tended to suppress the rate of conversion to the ketone. This can probably be explained by the additional production of water and cyclohexene (see below). Using a cyclohexanol/ferric chloride ratio in the optimum range at a given temperature, increasing the rhodium trichloride trihydrate concentration beyond a certain level did not significantly increase the final yield, or the reaction rate. The oxidation reaction occurred under acidic conditions, this acidity being the result of interaction between ferric chloride and cyclohexanol (and cyclohexanone) , The acidity of a typical system was found to decline rapidly as the reaction progressed. Cyclohexene was produced in a side reaction, together with water. This is presumably the result of cyclohexanol undergoing an elimination reaction under acidic conditions. Using the optimum cyclohexanol/ferric chloride ratio at 100deg, the the cyclohexene content remained at less than 10%, during the course of the reaction. Introduction of cyclohexene in amounts in excess of 20 % greatly suppressed the conversion to cyclohexanone, presumably due to strong complexation of the olefin with a rhodium species. water was produced during the catalytic oxidation in amounts greater than could be accounted for by production of cyclohexene. This additional water content of the reaction mixture in a closed system was in good agreement with that predicted on the basis of the equation: [ ] The presence of water in the reaction mixture tended to suppress the oxidation of cyclohexanol to cyclohexanone. Using the optimum ratio of components, very little conversion to the ketone occurred in the presence of oxygen, at temperatures below 50deg. Increasing the temperature from 100deg to 150deg increased the rate of oxidation but had little effect on the final yield of cyclohexanone. , Oxygen was found to be necessary for catalytic oxidation to occur. The measured oxygen absorption for a reaction mixture containing an optimum ratio of components, was found to be in good agreement with that predicted by the above equation. Using an optimum ratio of components in the presence of oxygen, the conversion to cyclohexanone was limited to approximately 40%. This limit was probably due to an interaction between cyclohexanone and some active rhodium species essential for catalytic activity. / Science, Faculty of / Chemistry, Department of / Graduate