Use of dye sensitized photooxidation is potentially a low cost means of degrading many of the hazardous compounds found in wastewaters. This study investigated the use of methylene blue as a sensitizer to degrade ortho-, meta-, and para-cresol, carbofuran and acrylonitrile. Significant reductions were found when aqueous solutions of the cresol isomers and carbofuran were illuminated and aerated in the presence of methylene blue. An average of 78% reduction of cresol was observed in seven hours. Carbofuran showed an average percent reduction of 56% in two hours. No loss was observed when the dye was absent. Acrylonitrile was found to be volatile and was stripped from solution by aeration. / M.S.

A comparative synthetic study of a series of six 1,2,3,4,5-pentaphenyl-2,4-cyclopentadiene alkyl ethers was investigated. It was determined that the most efficient route to these ethers was not the most generally accepted route to ethers - the Williamson Reaction - but rather a solvolysis reaction between 1-bromo-1,2,3,4,5-pentaphenyl-2,4-cyclopentadiene and the appropriate alcohol. Thermal rearrangement of the ethers had been expected to rearrange by a [1,5]-sigmatropic shift of the phenyl group in the 1-position to yield the corresponding enol ether. However, this appeared to occur only as a trace in some cases. Rather, the major product of the thermal rearrangements of these ethers was actually the elimination product, the hydrocarbon, 1,2,3,4,5-pentaphenyl-2,4-cyclopentadiene. The elimination is most likely the result of a retro-ene reaction. / Ph. D. / incomplete_metadata

The influence of alum concentration, pH and the molecular weight of organic substances present in a water were evaluated in regards to the removal of trihalomethane (THM) precursors from a surface water supply, Peak Creek, in southwestern Virginia. Water was coagulated with various doses of alum with the pH uncontrolled and with the pH controlled at 5.2 - 5.3. Raw water and treated waters selected for efficient turbidity and optimum total organic carbon (TOC) removals were concentrated 400X using vacuum evaporation at a temperature of 40° C. Concentrated waters were fractionated in regards to molecular weight (MW) with columns packed with Sephadex G-25 and G-75 gels. The fractionated samples were chlorinated for 96 hours and THM production was determined. A preliminary investigation explored the effect of coagulant alum concentration in regards to removal turbidity, TOC and THM precursors from VPI Duck Pond water. A second preliminary investigation involved determining the MW chromatographs of raw and treated Claytor Lake and Peak Creek waters concentrated to different degrees. The results indicated that THM precursors and heavier MW organic substances were preferentially removed from water by alum coagulation; that conducting alum coagulation at pH 5.2 - 5.3 induced more effective turbidity, TOC and THM precursor removals; and that TOC concentration was a more effective surrogate parameter than turbidity for determining the removal of THM precursors. / Master of Science

The foregoing paper reports a study on the effect of various organic compounds on the growth of Azotobacter. The study was induced by the theory that the soil contains organic substances which are deleterious to plant growth and which are important factors in influencing soil fertility. It is, therefore, interesting to determine if this toxicity extends to the lower plants. The Azotobacter was chosen as a representative of the soil flora since it is of recognized importance in the maintenance of the soil fertility and its growth may be accurately measured by analytical means. The compounds used were those likely to be constituents of the soil. The results of the study indicate that fixation of nitrogen by Azotobacter is only slightly influenced by most of the compounds investigated. A depression is noted in many cases but it is usually the result of a relatively high concentration of the compound used. Hydroquinone and Salicylic Aldehyde revealed the most toxic properties of any compounds studied. Esculin, Quinic Acid, and Borneal afforded marked stimulation to the growth of the organism. The effects of the compounds on Azotobacter are not, as a rule, in accord with what has been reported of their action on the higher plants. In concentrations which are fatal to certain higher plants, many of the compounds only slightly depressed fixation. A number of nitrogenous bodies were investigated. Such compounds as Nicotine, Picoline, and Skatol exhibited toxic properties commensurate to those usually ascribed to these substances. Caffeine appeared to stimulate the growth of the organism. Many of the nitrogenous compounds used which have been reported as beneficial to higher plants exercised a marked depression on fixation. It appears that the simpler compounds were more pronounced in this respect than were the more complex ones. It is suggested that this condition is not one of toxicity but that the nitrogen of the compounds was utilized by the Azotobacter in preference to that of the atmosphere. Urea, Glycocoll, Formamide, and Allantoin were especially active in depressing fixation. / Master of Science

The biosynthesis of virginiamycin S₁, a macrocyclic peptidolactone antibiotic, was studied by growing a strain of Streptomyces virginiae in a complex medium and observing the incorporation of radiolabeled compounds into the antibiotic. These studies have established several of the biosynthetic precursors of virginiamycin S₁. L-(U-14C)-Proline and L-(U-14C)-threonine were effectively incorporated into the respective amino acid components in the antibiotic. N-Methyl-L-phenylalanine was shown to arise from L-(U-14C)-phenylalanine and L-(methyl-14C)-methionine. L-(U-14C)-Phenylalanine was also efficiently incorporated into L-phenylglycine. The origin of the remaining three components was less clear. A small amount of L-(U-14C)-threonine was observed in D-α-aminobutyric acid. A biosynthetic pathway is known between these two amino acids which suggests that L-threonine may be the biosynthetic precursor of D-α-aminobutyric acid. Both L-(U-14C)-aspartic acid and L-(U-14C)-lysine were incorporated into 4-oxo-L-pipecolic acid and 3-hydroxypicolinic acid. A biosynthetic pathway was hypothesized to explain these results. / Master of Science

A formal total synthesis of aphidicolin, an important antitumor agent, has been accomplished. Completion of this synthesis required the development of novel methodology. Virtually all of the previous syntheses of aphidicolin share a common difficulty in the construction of the C-9 and C-10 vicinal quaternary centers. In order to solve this problem an investigation into the Michael reaction was launched. This study has revealed that steric encumbrance may be overcome by electronic activation of the acceptor. In fact, two withdrawing substituents were found to make possible the addition of the kinetic enolates of cyclohexenones to β, β-disubstituted acceptors. Several combinations of carboethoxy, cyano, and sulfinyl substituents were utilized. Also, use of sulfinyl butenolides as acceptors demonstrated that considerable stereochemical control may be exercised over the Michael reaction. In addition to work on the Michael reaction, the utility of a novel annulation procedure was demonstrated in the one-pot construction of the AB rings of aphidicolin. The required desulfurization of an α-sulfinyl lactone in the presence of an enone resulted in the development of a new, mild desulfurization agent. Some difficulty was encountered in the dissolving metal reduction of the A ring enone to provide the required trans decalin stereochemistry of the AB ring system of aphidicolin. However, this problem was solved by the construction of the D ring of aphidicolin prior to the dissolving metal reduction. This work resulted in the synthesis of an intermediate in Corey's total synthesis of aphidicolin. This synthesis is approximately 15 steps long, which is competitive with the shortest reported synthesis of aphidicolin. Furthermore, this synthesis is the most efficient reported to date, providing the natural product in approximately 10% overall yield. / Ph. D.

Three 2, 5-dialkyl-1, 3, 4-triphenyl-2, 4-cyclopentadien-1-ols and 2, 5-di(t-butyl)-1, 3-diphenyl-2, 4-cyclopentadien-1-ol were prepared from their precursor ketones using phenyllithium and Grignard reagent. In general, the phenyllithium reagent produced products faster and in better yield and purity than the Grignard reagent. The alcohols were rearranged thermally to obtain the appropriate ketones and to obtain information about the relative rates of the rearrangement. The rearrangement of the three 2, 5-dialkyl-1, 3, 4-triphenyl-2, 4-cyclopentadien-1-ols were studied kinetically and the results compared with those obtained from similar studies on 1,2,3,4,5-pentaphenyl-2,4-cyclopentadien-1-ol. The alcohols all possessed energies of activation and enthalpies of activation which were essentially identical, these supporting earlier theory that no linear free energy relationship (LFER) exists in these rearrangements and that a purely concerted mechanism exists in these cases. The rate of reaction for 15,16,17—triphenylbicyclo[12.2.1] heptadeca-14,16-dien-1-ol was very much faster than any other studied alcohol. The difference in this rate is thought to be due to the severe steric restraints that are present in this alcohol. The entropy of activation for this strained alcohol was shown. to be much less than for the other alcohols. / Ph. D.

Modifications of the potent anticancer agent taxol were carried out in order to gain an understanding of the chemical reactivity of the drug and the factors which contribute to its biological activity. The C-2' and/or the C-7 hydroxyl groups of taxol were substituted with acetyl, ßalanyl, silyl, succinyl, trichloroethyloxycarbonyl or carbonate linked dibenzylidene protected glucosyl groups. The C-7 position was selectively epimerized under free radical conditions and a 2'-epiacetyltaxol was produced via base catalysed epimerization. The C-2' amide became nucleophilic in the presence of base and could attack a C-2; acyl substituent. The C-13 ester side chain was selectively reduced by borohydride. The 7 position of taxol was selectively oxidized by Jones reagent and longer reaction times also oxidized the 2' position. The D rings of the 7 oxotaxols were readily opened via beta elimination; hydrogenation of the double bond in the enone of the D seco products produced a product in which the C ring was opened. The D ring was also susceptible to electrophilic attack. Reaction of taxol with triethyloxonium tetrafluoroborate or acetyl chloride/HC1 produced D seco taxols. C-7 deoxygenation was not achieved due to steric hindrance at C-7 and the instability of taxol under free radical conditions. Biological testing of modified taxols showed that substitution of the C-2' hydroxyl removed biological activity but that C-2' acyl groups were readily removed vivo. The water soluble 2'-βalanyItaxol possessed in vivo activity equal to that of taxol. Substitution of the C-7 hydroxyl did not inhibit the ability of a taxol derivative to polymerize tubulin but did decrease in vivo activity; epimerization of C-7 decreased in vivo activity slightly. A 2'-oxotaxol was found to be less active than, but still comparable to, its nonoxidized analogue. All taxol derivatives having a 7-oxo group and/or not possessing a D ring lost almost all biological activity. / Ph. D.

A series of eight l-substituted-2,3,4,5-tetraphenyl-2,4-cyclopentadien-l-ols were efficiently synthesized by the addition of the appropriate organometallic reagent to tetracyclone. It was determined that the steric and electronic nature of the migrating groups played a predictable role in the [l,5]-sigmatropic rearrangement of these compounds. Electron donating groups increased the rate of migration whereas electron withdrawing substituents were responsible for slowing the migration. Likewise, smaller groups accelerated the rate while bulky groups deterred the migration. Consequently, the experimental evidence supports the originally proposed charge separated transition state. The Michael addition of potassium cyanide to tetracyclone afforded upon protonation a diastereomeric mixture of the cis (kinetic product) and the trans (thermodynamic product) 4-cyano-2,3,4,5-tetraphenyl-2-cyclopenten-l-ones. Finally an efficient synthesis of 2,3,4,5-tetraphenyl-2(1H)-pyridinone (90%) resulted from the acid promoted addition of sodium azide to tetracyclone. The presence of an intermediate bicyclic triazoline eliminated the Schmitt mechanism as a viable reaction pathway. / Ph. D.

At present, South Africa has inadequate technology to destroy its hazardous waste, with approximately 18000 litres of chlorinated hazardous waste stored in this country. Approximately 800 tons of banned or obsolete chemicals are to be sent to Pontypool. Wales, for incineration, at a considerable cost. Because of the toxic nature of chlorinated waste and their long-term effects on the environment , a sustainable method of dealing with this type of waste is essential. Gas phase destruction of methylene chloride, trichlorobenzene and lindane by pyrolysis (i.e. heating in the absence of oxygen) was attempted. Destruction was effected by high temperature thermal degradation of molecules into free radicals. These radicals then combine to form hydrogen chloride and carbon as major products. This method was chosen so as to eliminate the possible formation of highly toxic oxygenated derivatives such as polychlorinated dibenzofurans and dibenzodioxins that can be formed during incineration if strict control is not excercised. The reactor assembly was built in the Department of Chemical Engineering at the University of Natal. 11 incorporates aspects of many different previously designed reactors, as discussed in the text. Heat for the reactions was supplied by induction. A high frequency induction unit supplied current to a copper coil. The resulting magnetic field induced current to flow in a susceptor housed within the copper coil. The susceptor in this case was a graphite tube, which served as both the heating element and the thermal radiation source, in addition to forming the walls of the reaction zone. Up and down stream processes were designed and experiments were carried out in which reaction temperatures (348-1400°C) and residence times (1.3-5.6 seconds) were varied. Destruction efficiencies of 100% and 99.99% were obtained for methylene chloride and trichlorobenzene respectively, with inert argon used as the carrier gas. These destruction efficiencies comply with the 99.99% stipulated by the United States Conservation and Recovery Act. A cause for concern was the formation of chlorinated benzenes and naphthalenes. Destruction of lindane proved unsuccessful due to limitations in the vapourisation and feed system and will have to be investigated further. The method of induction heating was evaluated to be 98.9% thermally efficient. Raw material and utility consumption per ton of waste destroyed by the pyrolysis process was compared to values for incineration as well as the plasma arc and catalytic extraction processes. Consumption for pyrolysis compares favourably with all three processes and suggests that the process could be competitive. Claims to the success of the technology on a wide scale are limited by the small number of compounds that were successfully pyrolysed. Results do however indicate much promise for this technology to be used as a fi nal chlorinated waste destruction unit on an existing process. Modifications to the existing reactor to improve product recovery and analys is will allow for temperature and residence time optimisation for a variety of wastes. Additional in strumentation and process control will allow for kinetic studies to be undertaken in future. This project should be considered as the first step in an ongoing series of research and subsequent improvements to the technology presented here. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.