Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: George Georgiou. Vita. Includes bibliographical references.

Thesis (MSc)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Thesis (M.S.)--Rochester Institute of Technology, 1992. / Typescript. Includes bibliographical references (leaves 82-85).

M.Sc. (Chemistry) / The isomerization of short chain olefins on a catalyst containing a H-X zeolite (HZ-1) produces mainly branched olefins at 400°C. At SASOL the catalyst is also used to reduce organic acids present in the feed. Amarked increase in the acid concentration over a period of time has been reported. Other impurities in the reactor feed include short chain alcohols, aldehydes and ketones. This study consisted of kinetic experiments which concentrated on the formation of acids from ketones and aldehydes during the isomerization of 1-hexene on 60/80 mesh HZ-1. The formation of acetic and propionic acid from methyl ethyl ketone was observed. It was also shown that n-butyrealdehyde forms formic acet ic, propionic and n-butyric acid at 400°C. The presence of n-buthanol during the reaction of methyl ethyl ketone enhanced the formation of acid. A supplementary study showed the formation of only acetic acid from acetone. The study of the formation of acids from a 5% methyl ethyl ketone/5% n-buthanol at 400, 300, 250, 200 and 150°C showed an overall decrease in the acid concentration with a lowering in temperature. These results showed the development of a definite maximum in the acid production. The formation of formic acid was also observed at 200 and 150°C. Amechanism for the formation of acids from ketones is proposed and discussed. Other than existing mechanisms this explains the formation of formic, acetic and propionic acid from methyl ethyl ketone. The mechanism includes Bronsted and Lewis acid sites. During this study a method was developed for the analysis of trace quantities of organic acids present in the reaction product. Ion exclusion chromatography was used for the quantitative determination of the different types of acids. Surface studies with nitrogen adsorptics showed a drastic decrease in the surface area during the reactions. Pore volume studies showed remarkably the loss of macropores' with a pore diameter bigger than 3,6 nm. Pikinometry showed the existance of micropores which were unaffected by the reactions. Aneutron activation analysis of HZ-l showed the presence of a great variety of transition elements mainly Scandium, Cobalt and Iron.

The past two years have witnessed groundbreaking advances in the industrial deployment of olefin metathesis. While metathesis methodologies have been an integral part of the chemical manufacturing landscape for 60 years, implementation in pharmaceutical and specialty chemicals manufacturing represents a new frontier. The imperative to develop greener and more cost-effective manufacturing processes is anticipated to spur further improvements in sustainable synthesis. Advances in catalyst productivity, however, are critical to expansion of the uptake of metathesis methodologies in this and other manufacturing sectors. Key to increased catalyst productivity is elimination of side reactions that lower yield and errode selectivity. Among such reactions, double-bond isomerization is by far most common. Accumulating evidence suggests that unwanted isomerization during olefin metathesis is due to ruthenium species generated via catalyst decomposition. The identification of these species and how they are formed is thus of great importance. Two hydride complexes, RuHCl(CO)(H2IMes)(PCy3) and a dinuclear hydride, are known to form under some circumstances by decomposition of the second-generation Grubbs catalyst, RuCl2(H2IMes)(PCy3)(=CHPh), GII. These complexes have been widely viewed as responsible for unintended isomerization reactions. However, examination of their performance in olefin isomerization under conditions relevant to metathesis reveals that their activity is too feeble to account for the levels of isomerization observed during metathesis. Alternatively, kinetically competent culprits emerge from decomposition studies that reveal unexpected ruthenium products on decomposition of GII during metathesis; specifically, formation of ruthenium nanoparticles. The formation and catalytic non-innocence of RuNPs constitutes a new paradigm in this field, which opens the door to new approaches to prevent or to harness olefin isomerization. Key to prevention, clearly, is circumventing the decomposition pathways that enable ligand stripping from the active catalyst. New approaches to catalyst design that involve use of truncated NHC ligands are also examined. Finally, the power and utility of isomerization when coupled with metathesis is explored. The opportunities and limitations of orthogonal isomerization–metathesis catalysis are examined in the context of the two-step synthesis of cinnamates from 1-allylbenzenes abundant in essential oils. An efficient one-pot, two-catalyst protocol is developed for conversion of these biorenewable feedstocks to high-value-added chemicals.

In the first part of this work the thermal reaction [Formula omitted] was studied thermodynamically and kinetically in the gas phase and at the temperature range 150 to 210°C. The equilibrium composition was found to be very unfavourable to 3-butenal which constitutes 0.35% of the mixture at 150°C and 1.04% at 210°C. The enthalpy of the reaction was estimated to be 7.20 ± 0.09 kcal/ mole. In the kinetic study both the forward and reverse reactions were found to be heterogeneous and of the first order with respect to surface area and pressure of reactant. The rate constants obeyed the relations [Equation omitted] k₁ was determined in a vessel with surface to volume ratio equal to 1.2 and k₋₁ in a vessel with ratio equal to 4.1. The significance of the experimental Arrhenius parameters was discussed in terms of the theory of absolute rates as applied to surface reactions and of a mechanism based on a fast adsorption-desorption of the Langmuir type. In the second part of the work the photochemical isomerization of crotonaldehyde to 3-butenal was studied in the gas phase and at the temperature range 25 to 140°C. Exciting radiation of the wavelengths 3130, 3340 and 3660 Å was used. It was found that the quantum yield of the isomerization obeys the Stern-Volmer equation 1/ϕ = a + bP ein/mole at the temperature and wavelength range studied. The pressure, P, of crotonaldehyde was varied from 0.4 to 34 mm Hg. The value of parameter a varies from 11 to 37 ein/mole with the low values observed at 3130 Å and the high values at 3660 Å. The parameter b varies from 0.19 to 7.5 ein.mole⁻¹ (mm Hg)⁻¹ with the low values also observed at the shorter wavelength. At constant wavelength b decreases with increasing temperature. A mechanism was discussed according to which the excited singlet '(n,π* ) is the reacting species and it was shown that a "strong collision" deactivation and a classical energy distribution function predict qualitatively the dependence of b on temperature and wavelength. An attempt to predict this dependence in a quantitative manner failed. A refinement to the "strong collision" mechanism using the same energy distribution function could not be tested numerically because of computational difficulties. An alternative mechanism was discussed involving a cis-trans equilibrium of crotonaldehyde in the ground state and it was shown that the parameters a and b may be interpreted in more than one way. In the third part of the work the photolysis and photochemical oxidation of 3-butenal were studied in the gas phase and the temperature range 25 to 140°C. In the photolysis exciting radiation of 3130 and 3340 Å was used. The products were carbon monoxide, propylene and biallyl. They were found to obey the relation CO ≤ propylene + 2.biallyl The overall quantum yields taken as equal to ϕ (propylene) + 2 ϕ (biallyl) obeys the Stern-Volmer equation (1). The Value of the parameter a varies from 0.994 to 1.226 ein/mole and that of b from 1.15 x 10⁻² to 3.75 x 10⁻² ein. mole⁻¹ (mm Hg)⁻¹ . The lowest values for both parameters are observed at 3130 Å and 140°C and the highest at 3340 Å and 25°C. The significance of parameter a was discussed and it was shown that its dependence on temperature and wavelength can be predicted within the limits of the experimental error by using the classical energy distribution function. In the photochemical oxidation radiation of 3130 Å was used. The major products with the quantum yields at 25°C shown in paranetheses were: carbon monoxide (3.0-3.4), allyl alcohol (1.1-2.4), acrolein (1.2-1.9), carbon dioxide (0.4-1.0), propylene (0.4-0.5), peroxide (0.20-0.27) and ethylene (0.22-0.27). Variation of the experimental conditions at constant temperature had little effect on the quantum yields. Increase of temperature to 140°C resulted in decrease of the yield of allyl alcohol and acrolein and increase of the yield of all the other products. A mechanism was discussed which explains the results in a qualitative way. / Science, Faculty of / Chemistry, Department of / Graduate

No description available.

The second order rate constants for nucleophilic substitution by methoxide of (Z)- and (E)-O-methylbenzohydroximoyl fluorides [C6H4C(F)=NOCH3] with various substituents on the phenyl ring [p-OCH3 (1h, 2h), p-CH3 (1g, 2g), p-Cl (1f, 2f), p-H (1e, 2e), (3,5)-bis-CF3 (1i, 2i)] in 90:10 DMSO:MeOH have been measured. A Hammett plot of these rate constants vs σ values gave positive ρ values of 2.95 (Z isomer) and 3.29 (E isomer). Comparison of these rates with methoxide substitution rates for Omethylbenzohydroximoyl bromide [C6H4C(Br)=NOCH3] and Omethylbenzohydroximoyl chloride [C6H4C(Cl)=NOCH3] reveal an element effect for the Z isomers of Br:Cl:F(1e) = 2.21:1.00:79.7 and for the E isomers of Cl:F(2e) = 1.00:18.3. With the p-OCH3-imidoyl halides the following element effects are found: Br:Cl:F(1h) = 2.78:1.00:73.1 for the Z isomer and Br:Cl:F(2h) = 1.97:1.00:12.1 for the E isomer. Measurement of activation parameters revealed ∆S≠ = -17 eu for 1e and ∆S≠ = -9.9 eu for 2e. Ab initio calculations (HF/6-31+G*, MP2/6-31+G*//HF/6-31+G*, B3LYP/6- 31+G*//HF/6-31+G*, HF-SCIPCM/6-31+G*//HF/6-31+G*) were performed to define the reaction surface. These calculations demonstrate a relatively large barrier for nucleophilic attack in relation to halogen loss and support the experimental findings that this reaction proceeds by an addition-elimination mechanism (AN# + DN). The imidoyl fluorides have been used to synthesize highly functionalized O-methyloximes by reaction with enolate anions derived from malononitrile, ethyl cyanoacetate, and diethyl malonate. Acid-catalyzed isomerization of compounds containing the O-methyloxime moiety have been investigated with ab initio calculations (HF/6-31+G*, MP2/6- 31+G*//HF/6-31+G*, B3LYP/6-31+G*//HF/6-31+G*). Barriers for rotation around the C-N bond following protonation have been calculated. The calculated barriers are discussed in relation to an isomerization mechanism of protonation-rotation versus a nucleophilic catalysis.

Dimethylsilene, generated from the thermal gas phase reaction of 1,1-dimethyl-1-silacyclobutane, reacts with alkynes to produce silacyclobutenes or acyclic silanes. The temperature dependence of the product ratios have been determined and the relative reactivities of three different alkynes toward the 1,1-dimethylsilene has been determined. 1-Hydrido-1-methylsilene has been generated by gas phase thermal decomposition from three different precursors. Trapping studies with butadiene and trimethylsilane lead to products expected from dimethylsilylene. The most plausible explanation for these observations is that hydridomethylsilenes undergo a facile isomerization to divalent dimethylsilylene. Cycloaddition of 1,1-dimethylsilene to allene at 600°C in a flow vacuum pyrolysis system affords the first synthesis of 2-methylene-1,1-dimethylsilacyclobutane and smaller amounts of six other products. For static pyrolysis at 421°C, the 2-methylene-1,1-dimethyIsilacyclobutane isomerizes to 1,1-dimethylsilacyclopentenes. The kinetics of gas phase thermal decomposition of cyclopropyltrimethylsilane has been studied over the temperature range, 689.6-751.1 K at pressures near 14 torr. The Arrhenius parameters for formation of allyltrimethylsilane are k_1(sec^-1)=10^14.3 ± 0.1 exp(-56.5 ± 0.2 kcal mol^-1/RT) and those for the formation of E- and Z-1-propenyltrimethyIsilane are k_2(sec^-1)=10^14.9 ± 0.3 exp(-61.9 ± 0.8 kcal mol^-1/RT). The difference between activation energies has been interpreted in terms of anchimeric assistance or the β effect of the silicon atom. The syntheses of 3-trimethylsilyl-1-pyrazoline and 1-trimethyl-2-pyrazoline are described. The thermal decomposition of either pyrazoline affords four different products along with elimination of a nitrogen molecule. It was suggested that the relative rates of methylene-hydrogen migration to radical centers α and γ to silicon are approximately equal. The thermal isomerization of 3-trimethylsilyl-1-pyrazoline to 1-trimethylsilyl-2-pyrazoline has been investigated kinetically at 65°C by proton NMR spectroscopy and the reverse reaction has been detected by gas phase pyrolysis.