Anion adsorption by clays, especially the negatively charged bentonitic clays, is a surprising phenomenon, since the negative charge of the clay is believed to be inherent in the lattice of the clay crystal.^1 The mechanism by which negatively charged ions are adsorbed by negatively charged surfaces is of considerable interest. The study reported in this thesis was carried out to gain an understanding of the mechanism of phosphate ion adsorption by the clays montmorillonite and kaolinite. To test the theory of phosphate ion adsorption by kaolinite that was proposed by Stout^2 and Kelley and Midgley^3, in which the surface layer of hydroxyl ions in the kaolinite lattice are considered to be exchangeable with phosphate ions, phosphated kaolinite was treated with varying amounts of sodium hydroxide and the solution in equilibrium with the clay was analysed for phosphate ions. Contrary to what one would predict from the anion exchange mechanism of Stout and Kelley and Midgley, less phosphate was replaced in solutions or high hydroxyl ion content than in low hydroxyl ion content. In order to determine if phosphate ion adsorption is affected by the type of cation adsorbed on the clay, samples or hydrogen saturated, phosphated montmorillonite were titrated to the equivalence point with sodium hydroxide, potassium hydroxide, and lithium hydroxide. This reduced sodium-saturated, potassium-saturated, and lithium-saturated clays. No differences in the amount or phosphate ion held by the clay whether saturated with hydrogen ion, sodium ion, potassium ion, or lithium ion was observed. It was concluded that phosphate ion adsorption is not a function of the type of cation (hydrogen ion, sodium ion, potassium ion, lithium ion) adsorbed by montmorillonite. To determine if adsorbed phosphate ions are exchangeable with other anions, samples of the phosphated montmorillonite and kaolinite were placed in solutions of varyings concentrations of eight different anions, chosen to represent a variety of sizes, structures, and valencies. Failure of adsorbed phosphate ions to exchange with any of these anions was interpreted as meaning that phosphate ion adsorption by montmorillonite and kaolinite is not a physical adsorption, but rather a specific chemical reaction. The hypothesis that phosphate ion adsorption by clays is a chemical precipitation of aluminum phosphate both by aluminum ions in solution (from dissolution of the clay) and aluminum ions exposed on the broken edges of montmorillonite and kaolinite crystals was proposed.

Calorimetric ΔH° values are given for stepwise proton dissociation from the protonated o-, m-, and p-aminobenzoic acids together with ΔH° values for proton ionization from the three corresponding methylaminobenzoates. The pK_1 values for the m- and p-aminobenzoic acids and pK values for the methylaminobenzoates were determined both by the entropy titration procedure and by the pH titration method. The pK_1 value for o-aminobenzoic acid was determined by entropy titration and the pK_2 values for o- and m-aminobenzoic acids were calculated from pH titration data. The ratios (K_Z) of the molar concentrations of zwitterion and neutral molecule for the three aminobenzoic acids were determined by both a pK method and a calorimetric method. An error analysis is made to provide insight into the relative merits of the two methods, and criteria are given which provide the best method for K_Z determination for any specific case. Microconstant, microenthalpy change, and microentropy change values are calculated for proton ionization from protonated m- and p-aminobenzoic acids from their respective K_Z and macrothermodynamic values. Previously, the calculation from calorimetric titration data of free energy, enthalpy, and entropy change values for protonation reactions in aqueous solution using stong acid or base solution as the titrant has been limited to substances whose pK values are either less than four or greater than ten. In this study, it is shown that the entropy titration method can be extended using weak acid or base solutions as titrants to cover the intermediate pK range ( 4>pK>10). To illustrate the applicability of this method using a weak acid titrant, pK, ΔH°, and ΔS° values for proton ionization from metanilic acid, pyridinium ion, imidazolium ion, protonated tris(hydroxymethyl)aminomethane and glycine have been determined from calorimetric titration data using a solution of acetic acid as titrant. Criteria are presented for titrant selection so the pK, ΔH°, and ΔS° values for any substance may be precisely and accurately determined by this method. A calorimetric study has been made of proton ionization from 71 protonated amines in aqueous solution at 25°. The resulting ΔH° values were combined with pK values to calculate ΔS° values. pK values were taken from the literature for 53 substances and new values were determined for 18 substances. A compilation of pK, ΔH° and ΔS° values from the present study and the literature is given for proton ionization from 171 amines. Hydrocarbon chain lengthening and branching effects on ΔH° and ΔS° values for proton ionization from primary and secondary aliphatic amines can be described by simple linear equations. Proton ionization from amines was not found to follow the linear relation between ΔG° and ΔS° predicted by the Bjerrum theory of electrostatics. The changes in ΔH° and ΔS° from the first to the second step of ionization for 37 diamines have been examined using the Bjerrum and Kirkwood-Westheimer theories of electrostatic interactions in aqueous solution. A deviation for the diamines, identical to that previously found for dicarboxylic acids, was found between the results derived from the experimental data and those predicted by the Kirkwood-Westhiemer theory. Possible reasons for this deviation are discussed.

A calorimetric study has been made of proton ionization in dilute aqueous solution from aliphatic carboxylic acids at 10, 25, and 40° (13 acids) and at 25° (3 acids). Values of ΔS° are calculated by combining the resulting ΔH° values with ΔG° values obtained from the literature or determined from potentiometric or calorimetric measurements. The trends in ΔG°, ΔH°, and ΔS° are described by an electrostatic model, and deviations from this model are taken as a measure of nonelectrostatic substituent effects for carboxylic acids. A calorimetric study has also been made of proton ionization in dilute aqueous solution from several primary, secondary and tertiary amines at 10, 25 and 40°. ΔCp° values have been calculated and correlations made between ΔCp° values for proton ionization of several acids and amines and the dipole moments of the unprotonated acids or bases. Linear enthalpy-entropy relationships have been observed for proton ionization as a function of temperature. An equation has been derived to use this linear relationship between ΔH° and ΔS° to calculate ΔG° values at temperatures where only ΔH° values are available.

The crystal structure of the barium thiocyanate complex of isomer A of the cyclic polyether dicyclo-hexyl-18-crown-6 has been determined by X-ray difraction techniques. It has been found that isomer A is in the cis-syn-cis conformation. Dicyclohexyl-18-crown-6 is prepared by hydrogenation of dibenzo-18-crown-6. Five isomers are possible as a result of this hydrogenation but only two have been isolated. ^1H and ^13C NMR results lead to trans and cis hydrogenation assignments, respectively. This study resolved the disagreement regarding the conformation differences between isomers. Log K, ΔH°, and ΔS° values for the hydrolysis and SO_4^= ion interaction of Al^3+ and Fe^3+ ions have been determined using an isothermal calorimetric titration procedure. The reactions were carried out in aqueous solution at 25° and ionic strengths of 0, 1.0, and 3.0, and also at 50° at an ionic strength of zero. Values of log K, ΔH°, and ΔS° valid at zero ionic strength and 10, 25 and 40° are reported for the interaction of dipicolinate ion with H^+, Mg^2+, Ca^2+, and Sr^2+ ions and for proton ionization from several cycloalkane-carboxylic acids and mono-substituted protonated pyridines.

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Master of Science / Department of Physics / Carlos Trallero / Over the past four decades, the single-electron ionization of atoms has been a subject of great interest within the ultra-fast community. While contemporary atomic ionization models tend to agree well with experiment across a wide range of intensities (10[superscript]13-10[superscript]15 W/cm[superscript]2), analogous models for the ionization of molecules are currently lacking in accuracy. The deficiencies present in molecular ionization models constitute a formidable barrier for experimentalists, who wish to model the single-electron ionization dynamics of molecules in intense laser fields. The primary motivation for the work presented in this thesis is to provide a comprehensive data set which can be used to improve existing models for the strong-field ionization of molecules. Our approach is to simultaneously measure the singly-charged ion yield of a diatomic molecule paired with a noble gas atom, both having commensurate ionization potentials. These measurements are taken as a function of the laser intensity, typically spanning two orders of magnitude (10[superscript]13-10[superscript]15 W/cm[superscript]2). By taking the ratio of the molecular to atomic yields as a function of laser intensity, it is possible to "cancel out" systematic errors which are common to both species, e.g. from laser instability, or temperature fluctuations. This technique is very powerful in our ionization studies, as it alludes to the distinct mechanisms leading to the ionization of both molecular and atomic species at the same intensity which are not a function of the experimental conditions. By using the accurate treatments of atomic ionization in tandem with existing molecular ionization models as a benchmark, we can use our experimental ratios to modify existing molecular ionization theories. We hope that the data procured in this thesis will be used in the development of more accurate treatments describing the strong-field ionization of molecules.