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Steel producers use various organic and inorganic coatings to protect cold-rolled steel (CRS) sheets from corrosion during shipment and storage. It is well known that CRS sheets can be protected from corrosion by galvanizing, phosphating, chromating, topcoating with organic, or their combinations. The chromate rinsing is particularly effective for preventing white rusting of galvanized steel. But there is an increasing interest in a replacement for the chromating process because of environmental and health concerns. The objective of the present work is to develop a chrome-free conversion coating for steel sheets. Various carboxylic acids and their salts have been studied for coating phosphated electrogalvanized (EG) steel sheets, including 10-undecenoic acid (UA), oleic acid (OA), and other fatty acids such as stearic acid (SA) and palmitic acid (PA). When they were used alone, or subsequently coated with resin, they could produce a highly hydrophobic surface and improve the corrosion resistance. Thiols such as 1-octadecanethiol (ODT) can form a self-assembled monolayer on metal substrates. This close-packed monolayer could provide an excellent corrosion resistance for EG steel sheets. It was capable of withstanding 50~60 hours of salt spray test (SST) although its thickness was only a few nanometers. The EG steel itself usually started rusting only after 2~4 hours of salt spray. In another coating system, thiols were mixed with a conventional resin to improve the corrosion resistance of EG steel. This new technique gave 100~120 hours of corrosion resistance. When the resin was applied directly on EG steel surface, its corrosion resistance was less than 72 hours. It was shown that further optimization of this technique increased the corrosion resistance to 200 hours and more in the standard SST. / Ph. D.

The scope of this research entailed the synthesis of novel polyorganosiloxanes with pendent phosphine, phosphine oxide, nitrile and carboxylic acid moieties. Such polysiloxanes were prepared with controlled concentrations of both the polar moieties and hydrido or vinyl pendent crosslinkable sites to afford precursor materials for well-defined networks. The intention was to generate stable microcomposite dispersions with very high concentrations of polar thermally conductive fillers. Lightly crosslinked elastomeric networks with controlled amounts of polar moieties were prepared via a hydrosilation curing mechanism. High concentrations of thermally conductive micro-fillers were dispersed throughout the resins and the microcomposites were investigated as thermally conductive adhesives. Random polysiloxane copolymers containing controlled number average molecular weights (Mns) and compositions with systematically varied concentrations of hydridomethylsiloxy- or vinylmethylsiloxy- units were prepared via ring-opening equilibrations of cyclosiloxane tetramers. These precursors were functionalized with precise concentrations of polar pendent moieties via hydrosilation (nitrile) or free radical addition reactions (phosphine and carboxylic acids). Valuable additions to the family of polysiloxanes were prepared by oxidizing the phosphine moieties to form phosphine oxide containing polysiloxanes. Defined concentrations of residual hydrido- or vinyl- reactive sites were crosslinked via hydrosilation to yield elastomeric adhesives. Specific interactions between the nitrile and phosphine oxide substituted polysiloxanes and the acidic proton of chloroform were shown using 1H NMR. The magnitude of the shift for the deshielded chloroform proton increased with the degree of hydrogen bonding, and was larger for the phosphine oxide species. The polar polysiloxane resins were filled with high concentrations of thermally conductive fillers including silica-coated AlN, Al spheres, BN and Ag flake, then hydrosilated to form microcomposite networks. Microcomposite adhesive strengths, thermal properties (glass transition temperature (Tg) and high temperature stability), and thermal conductivities were studied. An unfilled polysiloxane network containing only 15 mole percent phosphine oxide exhibited a dramatic improvement (46 N/m) in adhesive strength to Al adherends relative to a control polydimethylsiloxane network (2.5 N/m). Importantly, stable polysiloxane micro-dispersions were obtained with up to 67 volume percent (86 weight percent) silica-coated AlN. TEM data confirmed the dispersion homogeneity and XPS demonstrated that the particle surfaces were well-coated with the functionalized polysiloxanes. A microcomposite comprised of 67 volume percent silica-coated AlN and a polysiloxane containing only 9 molar percent nitrile groups had a thermal conductivity of 1.42 W/mK. The glass transition temperatures of the microcomposites were controlled by the amounts of polar functional moieties on the resins and the network crosslink densities. All of the microcomposites exhibited Tgs lower than -44°C and the materials remained stable in dynamic TGA measurements to approximately 400°C in both air and nitrogen. / Ph. D.

The growth of Fe₃O₄ and FeOOH crystals was investigated. Growth modifiers were used to alter the formation of iron oxides from ferrous hydroxide precipitates. Multifunctional carboxylic acids were found to have a strong influence on morphology of FeOOH. Dicarboxylic acids, containing two and seven carbons, changed the characteristics of α-FeOOH. These changes included alteration of the isoelectic point of the particulates and changes in particle size and shape. EDTA was found to alter the phase of FeOOH formation, favoring the synthesis of γ-FeOOH over α-FeOOH at temperatures below 50°C. The effects of multifunctional carboxylic acids were dependent upon the time of addition, and the presence of other growth modifiers. The changes in FeOOH formation were postulated to occur due to interaction between the acid molecules and Green Rust II, a common intermediate in iron oxide growth. The growth of Fe₃O₄ was found to be sensitive to solution pH, and the form of the iron starting materials. Examination of reaction intermediates by x-ray diffraction showed that other Crystalline phases formed prior to the production of Fe₃O₄. Different intermediate phases occurred depending on the amount of hydroxide in the reaction, and differences in Fe³⁺ starting materials. The production of different intermediate phases affected the morphology of Fe₃O₄. Early precipitation of Fe₃O₄ led to small particles, while formation of crystalline Fe(OH)₂ led to large crystals. Formation of a mixture of Green Rust II and Fe(OH)₂ early in the oxidation process led to formation of multiple nuclei, and produced smaller average particles with a wide particle size distribution. Fe₃O₄ particles prepared from α-FeOOH seed crystals were spherical, while Fe₃O₄ particles prepared from FeSO₄ alone were octahedral crystals. / Ph. D.

Despite its extremely low solubility in water, fullerite C₆₀ can form colloidally stable aqueous suspensions containing nanoscale C₆₀ particles (nC₆₀) when it is subject to contact with water. nC₆₀ is the primary fullerene form following its release to the environment. The aim of the present study was to provide fundamental insights into the properties and environmental impacts of nC₆₀. nC₆₀ suspensions containing negatively charged and heterogeneous nanoparticles were produced via extended mixing in the presence and absence of citrate and other carboxylates. These low-molecular weight acids were employed as simple surrogates of natural organic matter. The properties of nC₆₀ were characterized using dynamic light scattering (DLS), transmission electron microscopy (TEM), and UV-Vis spectroscopy. nC₆₀ produced in the presence of carboxylate differs from that produced in water alone (aq/nC₆₀) with respect to surface charge, average particle size, interfacial properties, and UV-Vis spectroscopic characteristics. Importantly, regularly shaped (spheres, triangles, squares, and nano-rods) nC₆₀ nanoparticles were observed in carboxylate solutions, but not in water alone. This observation indicates that a carboxylate-mediated 'bottom-up' process occurs in the presence of carboxylates. Changes in the UV-Vis spectra over time indicate that reactions between C₆₀ and water or other constituents in water never stop, potentially leading to significant morphologic changes during storage or as a result of simple dilution. These results suggest that studies examining the transport, fate, and environmental impacts of nC₆₀ should take the constituents of natural waters into consideration and that careful examination on the properties of the tested nC₆₀ should be conducted prior to and during each study. / Ph. D.

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Yes / Active packaging consisting of polyethylene terephthalate (PET) trays coated with a Citrus extract, without and with plasma pre-treatment, can reduce lipid oxidation in cooked meat. The mechanism of action of the packaging was investigated by quantifying the extent of transfer of antioxidant components from the active packaging into cooked turkey meat. Kinetic studies revealed the affinity for water of phenolic compounds and carboxylic acids in the Citrus extract, suggesting their diffusion into the water phase of the meat facilitated their antioxidant effect. Analysis by high-performance liquid chromatography permitted the identification of carboxylic acids and flavanones as major components of the extract. Their quantification in meat after contact with the trays revealed a release of 100% of the total coated amount for citric acid, 30% for salicylic acid, 75% for naringin and 58% for neohesperidin, supporting the release of these components into cooked meat as a mechanism of action of the antioxidant active packaging.

This thesis reports diverse synthetic and mechanistic studies in six chapters, as summarized below. Chapter 1. Revised mechanism and improved methodology for the perkin condensation.1 The generally accepted mechanism for the well-known Perkin condensation is unviable for at least two reasons: (1) the normally employed base, acetate ion, is too weak to deprotonate acetic anhydride (Ac2O, the substrate); and (2) even were Ac2O to be derprotonated , its anion would rapidly fragment to ketene and acetate ion at the high temperatures employed for the reaction. It has proved in this study that the Perkin condensation occurs most likely via the initial formation of a fem-diacetate (3, Scheme 1) from benzaldehyde (2) and acetic anhydride (1).1 The key nucleophile appears to be the enolate of 3 (and not of 1), which adds t the C=O group of the aldehyde 2 (present in equilibrium with 3). Thus cinnamic acid (4a) was formed in -75% yield with 3 as the substrate under the normal conditions of the Perkin reaction. The deprotonation of the diacetate appears to be electrophilically assisted by the neighbouring acetate group, the resulting enolate being also thermodynamically stabilized in form of an orthoester (I). The possibility that the diacetate 3 is the actual substrate in the Perkin reaction indicates that the reaction can be effected under far milder conditions, with a base much stronger than acetate ion. This was indeed realized with potassium t-butoxide in dioxane, which converted the gem-diacetates derived from a variety of aromatic aldehydes to the corresponding cinnamic acids (4), rapidly and in good yields at room temperature (Scheme 2). This represents a vast improvement in the synthetic protocol for the classical Perkin reaction, which remains an important carbon-carbon bond forming reaction to this day. Chapter 2. Aromaticity in azlactone anions and its sifnificance for the Erlenmeyer synthesis.2 The classical Erlenmeyer azlactone synthesis of amino acids occur via the formation of an intermediate azlactone, and its subsequent deprotonation by a relatively weak base(acetate ion),. The resulting azlactone anion (cf. II, Scheme 3) functions as a glycine enolate equilvalent, and is considered in situ with an aromatic aldehyde, subsequent dehydration leading to the 4-alkylidene oxazolone(analogously to the Perkin reaction). Interestingly, azlactone anions are possibly aromatic, as they possess 6π electrons in cyclic conjugation; this would explain their facile formation as also the overall success of the Erlenmeyer synthesis. The following studies evidence this possibility. The strategy involved studying the rates of base-catalyzed deprotonation in 2-phenyl-5(4H)-oxazolone (azlactone, 5) and its amide and ketone analogs, 3-methyl-2-phenyl-4(5H)-imidazolone (6), and 3,3-dimethyl-2-phenyl-493H)-pyrrolone (7) respectively.2 Two processes were studied, deuterium exchange and condensation with hexadeuteroacetone (Scheme3): both are presumably mediated by the anions II-IV, so their stabilities would govern the overall rates. These were followed by 1H NMR spectroscopy by monitoroing the disappearance of the resonance of the proton α to the carbonyl group. The order of deprotonation was found to be 6 > 5 > 7. However, the expected order based on pKa values would be ketone > ester > amide, i.e. 7 > 5 > 6. The inverted order observed strongly indicates the incursion of aromaticity, which would be enhanced by the electron-donor capabilities of the heteroatoms is 5 and 6. This is further substantiated by the greater reactivity in the case of the nitrogen analog 6 relative to the oxygen 5, which parallel the electronegativity order. (The aromaticity order would thus be: III > II > IV. The imidazole nucleus is indeed to be considerably more aromatic than the oxazole.) The synthesis of the analogs 6 and 7 was accomplished via an interesting intramolecular aza-Wittig reaction (Schemes 4 & 5) Chapter 3. Umpolung approach to the Erlenmeyer process in the synthesis of dehydro amino acids. These studies are based on the general observation that most of the strategies for the synthesis of α-amino acids introduce the side chain (or part was inverted in an umpolung sense. The key reaction studied was that of 2-phenyl-4-ethoxymethylne-5(4H)-oxazolone (11) with Grignard reagents: this resulted in the opening to yield a protected dehydro amino acid (12), in good to excellent yields (65-87%)(Scheme ^). As the azlactone reactant 11 is the ekectrophilic partner, this may be viewed as a partial umpolung version of the classical Erlenmeyer process. The readily available reactants, simple procedure and mild reaction conditions make this a very attractive method for the synthesis of a variety of α-dehydro amino acids. Chapter 4. The Erlenmeyer azlactone synthesis with aliphatic aldehydes under solvent-free microwave conditions. 3 A serious limitation to the classical Erlenmeyer reaction is that it generally fails in the case of aliphatic aldehydes. This chapter describes a convenient approach to this problem that extends the scope of the Erlenmeyer synthesis, via a novel microwave-induced, solvent-free process. This, it was observed that azlactones (5) react with aliphatic aldehydes (13) upon adsorption on neutral alumina and irradiation with microwaves (< 2 min), forming the corresponding Erlenmeyer products (14) in good yields (62-78%, Scheme 7). (The possible mechanistic basis of the procedure, which is presumably mediated by V , is discussed).3 Chapter 5. 2,4, 10-Trioxaadamantane as a carboxyl protecting group: application to the asymmetric synthesis of α-amino acids (umpolung approach).It is known that the 2,4,10-trioxaadamantane moiety is not only remarkably stable to nucleophilic attack, but can also be easily hydrolyzed to the corresponding carboxylic acid.4 It was of interest to apply this carboxyl protection strategy for designing a synthesis of α-amino acids, essentially by starting with a protected glyoxylic acid. The corresponding aldimine was expected to (nucleophilically) add organometallic reagents at the C=N moiety (cf. Shceme 8), the side chain of the amino acid being thus introduced in umpolung fashion. Also, a chiral aldimine would define an asymmetric synthesis of amino acids. Indeed, the chiral aldimine 17, derived from 2,4,10-troxaadamantane-3-carbaldehyde 15 and [(S)-(-)-1-phenylethylamine] 16, reacted with a variety of Grignard reagents to furnish the corresponding protected α-amino acids (18) in good yields, with moderate diastereometric excess (Scheme 8). Better yields and ‘de’ values were obtained with organolithium reagents. Chapter 6: possible one-pot oligopeptide synthesis with azlactones or amino acid N-carboxyanhydrides (NCAs). This chapter describes a novel approach to oligopeptide synthesis employing azlactones or NCA’s as amino acid equivalents which are simultaneously protected and activated (Scheme 9). Thus, the addition of the 4-substituted 2-benzyloxyazlactone (19) to an N-protected amino acid under basic conditions, was initially explored. The reaction was expected to yield a dipeptide (21) via the rearrangement of the mixed anhydride intermediate (VI) (Scheme 9). The subsequent addition of a different azlactone to the dipeptide (21) would analogously lead to the formation of a tripeptide (22). This may be performed repetitively to define a strategy for C-terminal extension of an oligopeptide chain, noting that no intervening deprotecting and activating steps are necessary. (In toto deprotection may be effected finally via the hydrogenolyis of the bvenzyloxy groups, to obtain 23.) A closely analogous strategy may also be envisaged by employing N.carboxyanhydrides (NCA’S, 24) instead of azlactones, as shown in Scheme 10 (forming dipeptide 26 and tripeptide 27). The main difference n this case is that the carbamic acid moiety of the intermediate mixed anhydride (VII) is expected to undergo decarboxylation to VIII (thus obviating the need for a deprotection step). However, this putative advantage is offset by the instability of NCA’s and their tendency toward polymerization. However, only partial success could be achieved in these attempts, although a variety of conditions were explored. The strategy and the experimental results have been analyzed in detail, as this interesting approach appears to be promising, and worth further study. (For structural formula pl refer the pdf file)

Exploiting coordination bonding of aromatic carboxylic acids at metal surfaces, this thesis explores new directions in the design and application of self-assembled monolayers (SAMs). The SAMs are investigated using a multi-technique approach comprising of a complementary combination of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. In addition, the X-ray standing wave technique (XSW) was used to characterise the substrates. The process of layer formation and the final structures of the SAMs are found to be strikingly dependent on the combination of molecule and substrate, which is discussed in terms of the intermolecular and molecule-substrate interactions, bonding geometries and symmetry of the organic molecules. This is illustrated by the dramatic difference between molecular adsorption on Ag and Cu for molecules such as biphenyl-3,4',5-tricarboxylic acid and biphenyl-4-acetic acid. In the case of self-assembly on Cu, the molecule-substrate interactions play a decisive role in the resulting SAM structure, whereas on Ag, the intermolecular interactions dominate over the weaker molecule-substrate binding. This exploration of the balance of interactions that lead to the formation of these SAM structures lays the foundation for a systematic design of the structures and properties of aromatic carboxylic acid based monolayers. Finally, different applications and properties of some SAMs were investigated, namely coordination of a Pd(II) complex to a pyridine/pyrazole terminated molecule adsorbed on Ag. Evidence of coordination of Pd(II) to single molecules was provided by STM, XPS and NEXAFS spectroscopy. Additionally, controlled STM tip induced modification of local areas of a 1,3,5-tris(4-carboxyphenyl)benzene SAM on Ag was performed, opening an exciting prospect for nanoscale molecular manipulation.