Several experiments were undertaken to investigate the mechanism of photodechlorination of pentachlorobenzene. The thermal methoxydechlorination reaction of pentachlorobenzene was studied. In DMSO at 50 °C sodium methoxide reacts smoothly with pentachlorobenzene to give three tetrachloroanisole isomers. A second-order kinetic plot for this reaction is linear to high precision, indicating that the reaction is second order overall. The rate of the reaction and the product regioisomer distribution are not affected by the presence of radical traps such as galvinoxyl, by reaction in the absence of oxygen or by benzyne intermediate traps such as 1,3-diphenylisobenzofuran. The rate of the reaction is reduced linearly as the starting mixture is diluted with methanol. These facts suggest that the reaction follows the classical S[subscript N]Ar mechanism. The proposed structure of the pentachlorobenzene radical anion formed by photolysis in the presence of triethylamine is analogous to the σ-complex intermediate in the S[subscript N]Ar reaction. The regiochemistry of these two types of dechlorination was compared and showed a fair correlation. The differences in regiochemistry were attributed to steric effects between the nucleophile and the aromatic ortho chlorine atoms in the S[subscript N]Ar reaction. Tetrachlorophenyl radicals were generated by thermal decomposition of 1 ,2,4,5-tetrachlorobenzeneazotriphenylmethane in the presence of CCl₄ and a hydrogen atom donor. The selectivies of chlorine versus hydrogen or deuterium atom abstraction were determined in several systems and applied to selectivity of atom abstraction observed in photochemical experiments. The results support the hypothesis that, in the photolysis of pentachlorobenzene in the presence of triethylamine, the intermediate tetrachlorophenyl radical exists as an unencumbered free radical rather than in a solvent caged pair with triethylamine. It was anticipated that the rate of photodechlorination would increase in micellar solutions if triethylamine was added. Experiments showed no such expected increase in rate, and showed regiochemistry similar to that of the same reaction in the absence of triethylamine. / Graduation date: 1992

Thesis (Ph. D.)--Ohio State University, 2009. / Title from first page of PDF file. Includes vita. Includes bibliographical references (p. 90-95).

Different sample preparation methodologies were evaluated for the determination of pollutants in different matrices. The methods investigated were chosen on the merits of decreased sample preparation time and low toxic solvent consumption with the aim to provide viable alternatives to more laborious methods, such as, Soxhlet extraction. Techniques were developed to extract and quantify organic pollutants from contaminated soils and water. The results from shake flask extraction of aged phenolic contaminated soils were used in attempt to relate sorption to both the soil, and pollutant properties. This was to help gain an understanding of the transport and fate of phenols in different environmental situations. The partitioning (sorption/desorption) of radiolabelled phenols between aqueous solution and soil was investigated using a modified shake flask technique. This provides additional information which can be related to soil characteristics, hence pertaining to the fate mechanisms involved for phenols in the environment. The results from these investigations suggest that more than one factor contributes to the sorption of phenols in soils.

No description available.

Submitted in complete fulfillment for the Degree of Master of Technology: Biotechnology, Durban University of Technology, Durban, South Africa, 2014. / Among persistent organic pollutants, chlorobenzenes are some of the most frequently encountered compounds in aqueous systems. These compounds can enter the environment via natural and anthropogenic sources, and are ubiquitous due to their extensive use over the past several decades. Several chlorobenzene compounds, once in the environment, can biologically accumulate, and are reputed to be carcinogens and extremely hazardous to health. Several chlorobenzenes are listed as priority pollutants by the United States Environmental Protection Agency. Excessive exposure to these compounds affects the central nervous system, irritates skin and upper respiratory tract, hardens skin and leads to haematological disorders including anaemia. In spite of these harmful effects, chlorobenzenes are still used widely as process solvents and raw materials in the manufacture of pesticides, chlorinated phenols, lubricants, disinfectants, pigments and dyes. In the light of the above, it is imperative to monitor the levels of chlorinated benzenes in all types of surface waters, using low-cost but sensitive methods of preconcentration and detection. In this study, a simple and relatively cheap preconcentration method using direct immersion solid phase microextraction (DI-SPME) followed by gas chromatography equipped with a flame ionisation detector (GC-FID) was developed for the analysis of 7 chlorinated benzenes in dam water. Experimental parameters affecting the extraction efficiency of the selected chlorobenzenes, such as fibre type, sample size, rate of agitation, salting-out effect and extraction time, were optimised and applied to the Grootdraai Dam water samples. The optimised method comprises the use of a 100 µm polydimethylsiloxane (PDMS) fibre coating; 5 ml sample size; 700 revolutions per minute rate of agitation and an extraction time of 30 minutes. The calibration curves were linear with correlation coefficients ranging from 0.9957–0.9995 for a concentration range of 1–100 ng/ml. The respective limits of detection and quantification for each analyte was as follows: 1,3-dichlorobenzene, 0.02 and 0.2 ng/ml; 1,4-dichlorobenzene, 0.04 and 0.4 ng/ml; 1,2-dichlorobenzene, 0.02 and 0.2 ng/ml; 1,2,4-trichlorobenzene, 0.3 and 2.7 ng/ml; 1,2,4,5-tetrachlorobenzene, 0.09 and 0.9 ng/ml; 1,2,3,4-tetrachlorobenzene, 0.07 and 0.7 ng/ml; pentachlorobenzene, 0.07 and 0.7 ng/ml. Recoveries ranged from 83.6–107.2% with relative standard deviation of less than 9%, indicating that the method has good precision, is reliable and free of matrix interferences. Water samples collected from the Grootdraai Dam were analysed using the optimised conditions to assess the potential of the method for trace level screening and quantification of chlorobenzenes. The method proved to be efficient, as 1,3 dichlorobenzene, 1,4-dichlorobenzene and pentachlorobenzene were detected at concentrations of 0.4 ng/ml, 1.7 ng/ml and 1.4 ng/ml, respectively.

Graduation date: 1995

Aqueous solubilities of twelve chlorinated benzenes were determined by two methods. In one method, the solutions in water were prepared by a vigorous stirring method followed by n-hexane extraction and GC-ECD analysis. In the second method, HPLC was used to prepare the saturated solutions. Experimental results were compared with the predictive values, the relative standard deviations are around 10%. Most of the chlorinated benzenes exhibit water induced transformations. The transformation products were either isomeric or with higher and lower numbers of chlorine substituents. The transformation phenomena can be explained by polarity, symmetry, reactivity of the chlorine atoms, and hydrophobic interactions. The mechanism of the transformation is governed by the radical mechanism.

The three isomers of dichlorobenzene (DCB) exhibit marked differences in hepatotoxicity following intraperitoneal (ip) administration in male F-344 rats. Plasma GPT activity, measured 24 hours post exposure, was elevated to approximately 4080 units/ml following a 1.8 mmol/kg dose of o-DCB. Conversely, n-DCB produced only a moderate elevation (306 units/ml) following a 4.5 mmol/kg dose, while p-DCB produced no elevation in GPT activity at this dose (24 units/ml). Ultra-structurally, o- and m-DCB induced elevations in GPT activity were associated with a centrilobular pattern of hepatic necrosis. The role of cytochrome P-450 mediated bioactivation in DCB-induced hepatotoxicity was demonstrated by elevated GPT activities following an otherwise nontoxic 0.9 mmol/kg dose of either o- or m-DCB in phenobarbital pretreated animals (16770 and 21540 units/ml, respectively). The paraisomer of DCB showed no induction of toxicity with phenobarbital pretreatment. Hepatic glutathione (GSH) concentrations were reduced 0.5, 3 and 5 hours after a 1.8 mmol/kg dose of either o- or m-DCB, a dose which produces hepatotoxicity only for o-DCB. Pretreatment of animals with phorone depleted hepatic GSH to 15% of control levels within two hours; subsequent ip administration of either o- or m-DCB (1.8 mmol/kg) produced approximately equivalent elevations in GPT activity for both isomers (5749 ± 648 and 4732 ± 857 units/ml, respectively). In vitro incubations of o- and m-DCB with GSH and rat liver cytosolic fraction, suggested that GSH may bind m-DCB without prior bioactivation, thereby reducing the hepatotoxicity of this isomer relative to the more toxic ortho isomer. The interactive hepatotoxicity of the dichlorobenzenes with carbon tetrachloride (CCl₄) was also investigated. Concomitant ip injection of CCl₄ (1.0 mmol/kg) and o-DCB (2.7 mmol/kg) produced a marked inhibition of o-DCB hepatotoxicity, as measured by GPT activity (approximately 200 units/ml vs. 7450 units/ml for o-DCB alone). The mechanism of this inhibition of o-DCB hepatotoxicity was shown to be a reduction in the cytochrome P-450 mediated bioactivation of o-DCB, by CCl₄. A similar inhibition of o-DCB hepatotoxicity was seen following administration of CCl₄ as a pretreatment, via the drinking water. Concomitant ip administration of CCl₄ with either m- or p-DCB also produced a reduction in the metabolism of the dichlorobenzene.

The sulfonation of chlorobenzene, chlorobenzene-benzene, and toluene-benzene mixtures by sulfur trioxide in liquid sulfur dioxide at -12.5° C. was studied to obtain isomer distribution and relative rate data. The isomer distribution for the reaction on chlorobenzene was determined by an isotope dillution technique. Relative rate experiments were conducted by sulfonating C14 labeled benzene in competition with nonradioactive chlorobenzene and toluene and the count rate of the products was used to determine product composition. Ultraviolet spectrophotometry was also used to investigate variations in isomer distributions as a function of sulfur trioxide concentration. The apparent relative rates of sulfonation (kX/kB) as calculated by Ingold's equation, vary with both the initial ratio of arenes and the concentration of sulfur trioxide. The ortho/para ratio decreases with increasing sulfur trioxide concentration. These observations are explained in terms of secondary sulfonation reactions which produce significant amounts of product sulfonic acids by reaction of the arenes with reagents other than sulfur trioxide. The secondary sulfonating agents are presumed to be sulfonic acid anhydrides and/or pyrosulfonic acids. The secondary reactions contribute proportionately more to the total product of that species formed in the smaller amounts by the primary reaction. Criteria for the applicability of Ingold's equation are discussed in connection with the possibility of secondary reactions. Relative rate constants for competitive chlorobenzene:benzene and toluene:benzene sulfonation with sulfur trioxide, corrected for secondary reaction effects, are 0.087±0.002 and 27.0±1.0 respectively. The observed isomer distribution for the sulfonation of chlorobenzene is o = 0.95 ± 0.03%, m = 0.09 ± 0.02%, and p = 98.96 ± 0.12%. Partial rate factors calculated for the sulfonation of chlorobenzene and toluene are pf = 0.517, of = 0.0025, mf = 0.00024 and pf = 144.6, of = 81.2, and mf = 0.59 respectively. Neither sulfonation fits the selectivity relationship predicted for it, although correction for secondary reaction effects greatly improves the fit for the toluene data. The deviation of the toluene data from the selectivity relationship probably results from a low percentage of meta isomer in the reported isomer distribution for toluene.

Methods of determining the aqueous solubilities of twelve chlorinated benzenes were evaluated in pure and in different water matrices. In pure water, results were comparable with the calculated values. Higher chlorinated tetrachlorobenzenes (TeCBs), pentachlorobenzenes (PCBz), and hexachlorobenzenes (HCBs) gave better precision and accuracy than lower chlorinated monochlorobenzenes (MCBs), dichlorobenzenes (DCBs), or trichlorobenzenes (TCBs).