Boron acid complexation reactions in basic solution.
Item
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Title
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Boron acid complexation reactions in basic solution.
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Identifier
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AAI9119685
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identifier
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9119685
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Creator
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Tihal, Cherryl Ann.
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Contributor
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Adviser: Richard Pizer
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Date
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1991
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Inorganic
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Abstract
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Boron acids are Lewis acids and ionize in solution to produce four-coordinate, tetrahedral borate anions. Both the trigonal boron acid and the tetrahedral borate anion can react with bidentate chelating ligands (such as {dollar}\alpha{dollar}-hydroxycarboxylic acids) to produce the same four-coordinate chelate complex. For the reactions between the trigonal boron acids and fully protonated ligands, the proposed transition state is characterized by a mechanism which involves proton transfer. The present study was designed to investigate the following: (1) the reactivity of the borate anion towards bidentate ligands, (2) the effect on the reaction mechanism when the ligand contains no acidic protons, (3) the measurement of the enthalpy and entropy changes for borate chelation reactions, and (4) the interaction between boron acids and simple unidentate ligands.;The ligands used are simple polyols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol and glycerol. The kinetic results show that the trigonal boron acids are unreactive toward the polyols while the four-coordinate borate anions are much more reactive. The lability of four-coordinate borate anions may be a consequence of the longer boron-oxygen bond relative to the trigonal species, but we are unable at this point to propose a transition state for these reactions.;The complexation reactions between the borate anion and the polyols are spontaneous. Therefore, the measurement of the enthalpy and entropy changes allows one to determine whether the driving force for the reactions is enthalpic or entropic in origin. These thermodynamic measurements indicate that the reactions of borate with the polyols are enthalpy driven.;The reactions between boron acids and peroxo ligands produce complexes in which the ligand is unidentate. Boric acid and hydrogen peroxide interact to form the following complexes: (OH){dollar}\sb3{dollar}BOOH{dollar}\sp-{dollar}, (OH){dollar}\sb2{dollar}B(OOH){dollar}\sb2\sp-{dollar} and (OH){dollar}\sb2{dollar}BOOH. Equilibrium constants were determined quantitatively but no kinetic study was possible due to the decomposition of hydrogen peroxide under our experimental conditions. No determination of equilibrium constants was possible in the phenylboronic acid/hydrogen peroxide system because of the oxidation of the boron acid by the ligand. In the boric acid/tert-butylhydroperoxide system, complex formation was negligible.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
