Synthesis and characterization of polynitro-[2.2]paracyclophanes, a novel xylylene polymer, and poly(p-phenylene sulfoxide).

A less closely related polymer, poly(p-phenylene sulfoxide) (PPSX) (18) was synthesized by a novel homogenous oxidation of poly(p-phenylene sulfide) 17 with neat fuming nitric acid, fuming nitric acid in trifluoroacetic acid (TFA), and concentrated nitric acid in TFA. Several model compounds and modified reactions were studied which implicated a nitrogen oxide adduct as a major and required element in the selective oxidation to the polysulfoxide rather than the polysulfone. The intrinsic viscosity of the PPSX polymer was determined to be 0.274. PPSX was successfully fractionated yielding a high molecular weight polymer identified by GPC (Mw = 84,000 and Mn = 30,800). Multiple unitary and binary solvent systems were identified for PPSX, and clear, free-standing, flexible films were cast with plasticizer enhancement. Thermal analysis identified PPSX as an amorphous polymer with a decomposition temperature in air of 334° C and in helium of 342° C. The activation energies of the thermal decomposition of PPSX in air and helium were determined by the Friedman method to be 32 +/- 6 and 31 +/- 3 kcal/mol, respectively. PPSX successfully demonstrated the ability to chelate several metals in experiments intended to explore metal extraction applications.A novel polymer derived from these synthetic routes, poly(2,6-dimethyl- p-xylylene) (21), was synthesized and characterized. This amorphous, soluble polymer had the highest molecular weight of any literature reported xylylene polymer measured by GPC (Mw = 150,500 and Mn = 60,5 10). The polymer 21 exhibited excellent thermal stability in helium and air. The onset of thermal decomposition in air (424° C) was more than 100° C higher than all non-fluorinated xylylene polymers. Excellent quality, freestanding, flexible films of 21 were cast from chloroform.With the goal of better understanding previously documented, structurally related, exothermic decompositions of polynitro-paracyclophanes (polynitroPCP), two novel tetramethyl-tetranitro-[2.2]paracyclophanes and their related polymer were synthesized and characterized: 4,8,12,16-tetramethyl-5,7,13,15-tetranitro[2.2]paracyclophane (45) and 4,8,13,15-tetramethyl-5,7,12,16-tetranitro[2.2]paracyclophane (46), and poly(2,6-dimethyl-3, 5-dinitro-p-xylylene) (20). These compounds and previously synthesized dinitro[2.2]PCP's were characterized by DSC thermal analysis techniques. Compounds 45, 46, and 20 decomposed exothermically at 314, 303, and 281° C, respectively. The exothermic decompositions of the polynitroPCP's are not a product of the strain in the dimer [2.2]PCP members of this class, but rather a feature of the ethano bridge system. The elevation of the decomposition temperatures by 33° C in the non-polymer polynitroPCP's is likely due to an attenuation of intermolecular nitro group interactions caused by intramolecular nitro group orientation restrictions. A smaller 10° C decomposition temperature variation in the dinitro[2.2]PCP's follows a similar trend of likely nitro group orientation restrictions. The severely basic and nucleophilic conditions of the Hofmann elimination also proved incompatible to the synthesis of less methylated polynitroPCP's

Investigation of Novel Quasiliving Polyisobutylene Chain-end Functionalization (Quenching) Methods

This volume recounts efforts toward the development and understanding of chain functionalization techniques involving the direct addition of nucleophiles to quasiliving polyisobutylene (PIB). Nucleophiles included in the study were sterically hindered organic bases, (di)sulfides, N-substituted pyrroles, and alkoxybenzenes. A kinetic investigation of the end-quenching of TiCl4-catalyzed quasiliving PIB with sterically hindered amines was used to determine the mode of interaction with TiCl4 and the active species responsible for -proton abstraction. 2,5-disubstituted-N-hydropyrroles formed pyrrole-TiCl3 adducts that were active in formation of exo-olefin chain ends; whereas, with other sterically hindered amines, only an equilibrium fraction of the amine that did not complex with TiCl4 remained available for proton abstraction. Low-temperaturestable sulfonium ion adducts were generated by addition of mono- and disulfides to TiCl4-catalyzed quasiliving PIB. At temperatures less than or equal to -60 oC, quantitative 1:1 adducts were formed between the (di)sulfides and the oligo-isobutylenes. When a more reactive nucleophile such as an alcohol or amine was added to the reaction, the adducts were destroyed, and both elimination and substitution products were obtained. N-(2-tert-Butoxyethyl)pyrrole was used to end-quench TiCl4-catalyzed quasiliving PIB and resulted in near quantitative end-capping, except for the formation of \u3c5% exo-olefin chain ends, with alkylation occurring in both the C-3 (57%) and C-2 (38%) position on the pyrrole ring. Further treatment with acids and warming resulted in alkylation via the residual olefin and rapid cleavage of the terminal tert-butyl group of the N-(2-tert-butoxyethyl)pyrrole-capped PIB to provide hydroxyl end group functionality in situ. Alkoxybenzenes were also used to end-quench TiCl4-catalyzed quasiliving isobutylene polymerizations. Successfully alkylated alkoxybenzenes included those with alkyl tethers, such as anisole and isopropoxybenzene, those with haloalkyl tethers, such as (3-bromopropoxy)benzene and (2-chloroethoxy)benzene, and even those with hydroxyl and amine functionality, such as 4-phenoxybutanol and 6-phenoxyhexylamine. Alkylation occurred exclusively in the para position of alkoxybenzenes, and multiple alkylations were not observed. The alkylation reactions were tolerant of temperatures ranging from -70 to -30 oC and were unimpeded by the presence of endo- or exo-olefin termini. Terminal ether cleavage for polyisobutylenes capped with anisole and isopropoxybenzene allowed single-pot synthesis of phenol telechelics

The radiation-induced degradation of poly(diene sulfones) as x-ray resists

The microlithographic process, essential in the fabrication of silicon chip integrated circuits, uses high-energy radiation to transfer a pattern onto a thin film of polymer resist. Pattern transfer occurs by modifying the properties (solubility or volatility) of the polymer film exposed to radiation. Poly(olefin sulfones) exhibit a high sensitivity to x-rays, which is a desirable property for polymer resists, but typically undergo a glass transition around room temperature and a thermal degradation at moderate temperatures. The thermal properties of the poly(olefin sulfones) reduce the processing latitude for industrial microelectronics applications. Poly(unsaturated olefin sulfones) containing a carbon-carbon double bond in the polymer backbone exhibit good thermal stability and film forming properties comparable to those observed with poly(methyl methacrylate), PMMA. The potential utility of these new resins prompted a study of the mechanism of degradation promoted by x-ray radiation. In this study, the effect of x-ray radiation on polysulfones with varied chemical structures was analyzed using x-ray absorption near-edge structure (XANES) spectroscopy. The volatile by-products formed upon irradiation of each polysulfone were characterized by in-situ mass spectroscopy. Distinct differences between the mode of degradation of poly(olefin sulfones) such as poly(butane-1 sulfone), PBS,and that of poly(hexadiene sulfone), PHS, were observed. The energy positions of the sulfur K-edge in irradiated PBS are approximately 2473 eV, (sulfide) and 2479 eV (sulfone). Decomposition is accompanied by sulfide formation and the evolution of butene-1 in the gaseous by-products. In contrast, the sulfur K edge spectra of PHS exhibits the following energy positions, 2473 eV (sulfide), 2475 eV (sulfoxide), 2478 eV (sulfone) and 2482 eV (sulfonate). Only sulfur oxide by-products were observed in the mass spectra indicating that the predominant mode of degradation is oxidative. Further studies will be required to elucidate the mechanism of this new mode of degradation

Kinetic studies about the oxidation of hydrogen sulfide with iron aminopolycarboxylate complexes in presence of dissolved oxygen : relevance to other reduced sulfur compounds originating from kraft pulping

Tableau d'honneur de la Faculté des études supérieures et postdoctorales, 2006-200

Implications of reactive oxygen species (ROS) in initiating chemical reactions

This thesis presents a series of scientific studies exploring the initiation of various chemical reactions with reactive oxygen species (ROS), mainly singlet oxygen. These studies have revealed new mechanistic insights in environmental, industrial and biological systems, have described the associated set of reactions, have illustrated the detection of new radicals i.e., environmentally persistent free radicals (EPFR), and have provided a new insight explaining the spontaneous fire in coal mines. Comprehensive experimental and quantum-mechanical calculations afforded the investigation of oxidation reactions of singlet oxygen with wastewater organic contaminants, for example, the photodegradation of Phenol and Aniline in water. Detailed experimental studies on modelled surrogates, i.e., Anisole, resolved the fundamentals of thermal interaction of coal with iron oxide Fe2O3 nanoparticles. Along the same line of interest, enhancing the combustion efficiency of fuel constitutes a mainstream strategy in the pursuit of meeting the ever-increasing energy demand. Therefore, this thesis also provides a comprehensive mechanistic and thermo-kinetic accounts underpinning the reaction of fuel surrogates, namely Toluene, with singlet oxygen in the internal combustion (IC) engines. Finally, this work extends insights into biological systems, mapping the Alloxan-Glutathione redox cycle to expose the formation of ROS, species that eventually cause necrosis of the pancreatic insulin-producing beta cells and prompt the insulin-dependent diabetes mellitus (IDDM). The methodology involve customised LED-photoreactors, thermal packed-bed reactor, and various reaction product-monitoring systems, e.g., Fourier transform infrared spectroscopy (FTIR) to quantitate the ignition temperatures of fuel surrogates, in-situ electron paramagnetic resonance (EPR) to elucidate the formation of environmentally-persistent free radicals (EPFR) as well as intermediate radical species, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to monitor the chemisorption of organic substrates on the nanoparticles, X-ray diffraction for particles characterisation, as well as broad-scan UV-Vis spectroscopy and high-performance liquid chromatography (HPLC) to identify and quantify the intermediate and product species in solutions. Results obtained in this thesis elucidate, for the very first time, the formation of para-semibenzoquinone anion (PSBQ) supporting the reaction pathway leading to the formation of para-benzoquinone during the reaction of phenol (and aniline) with singlet oxygen. These results have practical application to quantify the degradation of organic pollutants in wastewater. Investigations regarding combustion applications shows that the presence of singlet oxygen considerably lowers the activation energy of the initiation channels of aromatic hydrocarbons (e.g., in IC engines), resulting in an energetically improved combustion process, the relative reactivity of singlet oxygen, based on the reaction rate constants, follows the order of OH > H > CH3 > 1O2 > HO2 > 3O2. Furthermore, the chemisorption of anisole on α-Fe2O3 surfaces has been elucidated to follow a direct dissociation of the O–CH3 (and OCH2–H), leading to the formation of surface-bound phenoxy radicals and gaseous species at temperatures as low as 25 °C. This insight applies to free-radical chain reactions that induce spontaneous fires of coal, as low-ranked coal comprises ferric oxide nanoparticles, and equally, to coexistence of aromatic fuels with thermodynamically reactive Fe2O3 surface, e.g., in fly ash, at the cooled-down tail of combustion stacks. Results from alloxan-glutathione redox cycle clarified, for the first time, the direct synchronised generation of dialuric acid radical (DA˙) and glutathione radical (GS˙), assigning the nature of the mysterious “compound 305” to the DA˙- GS˙ complex. These results explain the alloxan-induced diabetes on precise molecular bases. This thesis provides new perspectives on opportunities in understanding the influence of ROS, mainly singlet oxygen (1O2) and superoxide (O2−) in germane chemical reactions. Such attempts will advance the existing ROS-related technologies, and improve the fundamental theories in supports of environmental management and application decisions

Anodic Cyclization Reaction: Manipulation of Reaction Pathway and Efforts to Radical Cation and Radical Intermediate

In recent years, synthetic chemists have been expressing significant interest in electro-organic synthetic methods. This interest is being fueled by the existence of an increasing number of successful methods in the literature and the availability of new electrochemical equipment that removes the barrier to attempting an electrolysis reaction for the first time. Yet while these developments have fueled growth in some areas of electro-organic synthesis (the recycling of chemical catalysts for example), other areas remain underdeveloped. One such area is the exploration of reactions that can be triggered directly as an electrode surface without the use of any chemical reagent. Such reactions lead to highly reactive intermediates that allow for entirely new modes of reactivity to be explored. For example, our group has been working to develop anodic oxidation reactions that convert electron rich olefins into reactive radical cation intermediates. The reactions lead to a reversal in the polarity of the original olefin that enable the normally nucleophilic groups to be used as electrophiles. The result is an opportunity to change the entire manner in which the synthesis of a complex target is approached. Simply put, new modes of reactivity offer an opportunity to not only change the way individual steps in a synthetic sequence are conducted but also change the overall route because groups that normally function in a certain manner no longer behave the same way. While efforts to demonstrate the power of these opportunities have been successful for a variety of reactions in the group, our ability to continue forwarding the chemistry into even newer areas relies on our continuing to expand our knowledge of the reactive intermediates involved in electrochemical oxidation reactions, how they behave, and how they can be channeled down productive pathways. With this in mind, the main focus of this dissertation is to build our understanding of the reactive intermediates involved in anodic cyclization reactions and how those intermediates can best be applied as synthetic tools. The work probes the advantage of directly using the radical cations intermediates generated at an anode for triggering bond formation relative to pushing the reactions away from pathways that utilize the radical cation and toward pathways that involve an oxidative radical pathway. Along these lines, a synthetic route that allows both pathways to be accessed from the same starting materials has been developed. Using the chemistry, reactions that generate seven membered ring products and oxidative tandem cyclization reactions have been explored. In addition to these studies, an example of how optimizing a reaction sometimes requires one to pay attention to intermediates downstream of the cyclization is reported. Finally, the electrochemical method has been extended to an example of how it can be used in the synthesis of a complex molecular surface