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- All Subjects: Geochemistry
- All Subjects: Bipyridine
- Creators: Gould, Ian R
- Member of: ASU Electronic Theses and Dissertations
- Status: Published
Description
The hydrothermal chemistry of organic compounds influences many critical geological processes, including the formation of oil and gas reservoirs, the degradation and transport of organic matter in sedimentary basins, metabolic cycles in the deep subsurface biosphere, and possibly prebiotic organic synthesis related to the origin of life. In most previous studies of hydrothermal organic reactions the emphasis has been mainly on determining reaction product distributions, studies that provide detailed mechanistic information or direct evidence for specific reaction intermediates are rare. To develop a better understanding, I performed hydrothermal experiments with model ketone compound dibenzylketone (DBK), which serves as a quite useful tool to probe the bond breaking and forming processes in hydrothermal geochemical transformations. A careful study of reaction kinetics and products of DBK in Chapter 2 of this dissertation reveals reversible and irreversible reaction pathways, and provides evidence for competing ionic and radical reaction mechanisms. The majority of the observed products result from homolytic carbon-carbon and carbon-hydrogen bond cleavage and secondary coupling reactions of the benzyl and related radical intermediates.
In the third chapter of the dissertation, a novel hydrothermal photochemical method is studied, which enabled in situ independent generation of the relevant radicals and effectively separated the radical and ionic reactions that occur simultaneously in pure thermal reactions. In the following chapter, I focus on the role of minerals on ketone hydrothermal reactions. Minerals such as quartz and corundum have no detectable effect on DBK, whereas magnetite, hematite, and troilite all increase ketone reactivity to various extents. The influence of these iron-bearing minerals can be attributed to the mineral surface catalysis or the solution chemistry change that is presumably caused by dissolved inorganic species from minerals. In addition, some new discoveries on strong oxidizing effect of copper (II) ion under hydrothermal conditions are described in the latter chapter of the dissertation, where examples of clean and rapid reactions that converted alcohols to aldehyde and aldehydes to carboxylic acids are included.
In the third chapter of the dissertation, a novel hydrothermal photochemical method is studied, which enabled in situ independent generation of the relevant radicals and effectively separated the radical and ionic reactions that occur simultaneously in pure thermal reactions. In the following chapter, I focus on the role of minerals on ketone hydrothermal reactions. Minerals such as quartz and corundum have no detectable effect on DBK, whereas magnetite, hematite, and troilite all increase ketone reactivity to various extents. The influence of these iron-bearing minerals can be attributed to the mineral surface catalysis or the solution chemistry change that is presumably caused by dissolved inorganic species from minerals. In addition, some new discoveries on strong oxidizing effect of copper (II) ion under hydrothermal conditions are described in the latter chapter of the dissertation, where examples of clean and rapid reactions that converted alcohols to aldehyde and aldehydes to carboxylic acids are included.
ContributorsYang, Ziming (Author) / Shock, Everett L (Thesis advisor) / Gould, Ian R (Committee member) / Wolf, George H. (Committee member) / Arizona State University (Publisher)
Created2014
Description
Increasing concentrations of carbon dioxide in the atmosphere will inevitably lead to long-term changes in climate that can have serious consequences. Controlling anthropogenic emission of carbon dioxide into the atmosphere, however, represents a significant technological challenge. Various chemical approaches have been suggested, perhaps the most promising of these is based on electrochemical trapping of carbon dioxide using pyridine and derivatives. Optimization of this process requires a detailed understanding of the mechanisms of the reactions of reduced pyridines with carbon dioxide, which are not currently well known. This thesis describes a detailed mechanistic study of the nucleophilic and Bronsted basic properties of the radical anion of bipyridine as a model pyridine derivative, formed by one-electron reduction, with particular emphasis on the reactions with carbon dioxide. A time-resolved spectroscopic method was used to characterize the key intermediates and determine the kinetics of the reactions of the radical anion and its protonated radical form. Using a pulsed nanosecond laser, the bipyridine radical anion could be generated in-situ in less than 100 ns, which allows fast reactions to be monitored in real time. The bipyridine radical anion was found to be a very powerful one-electron donor, Bronsted base and nucleophile. It reacts by addition to the C=O bonds of ketones with a bimolecular rate constant around 1* 107 M-1 s-1. These are among the fastest nucleophilic additions that have been reported in literature. Temperature dependence studies demonstrate very low activation energies and large Arrhenius pre-exponential parameters, consistent with very high reactivity. The kinetics of E2 elimination, where the radical anion acts as a base, and SN2 substitution, where the radical anion acts as a nucleophile, are also characterized by large bimolecular rate constants in the range ca. 106 - 107 M-1 s-1. The pKa of the bipyridine radical anion was measured using a kinetic method and analysis of the data using a Marcus theory model for proton transfer. The bipyridine radical anion is found to have a pKa of 40±5 in DMSO. The reorganization energy for the proton transfer reaction was found to be 70±5 kJ/mol. The bipyridine radical anion was found to react very rapidly with carbon dioxide, with a bimolecular rate constant of 1* 108 M-1 s-1 and a small activation energy, whereas the protonated radical reacted with carbon dioxide with a rate constant that was too small to measure. The kinetic and thermodynamic data obtained in this work can be used to understand the mechanisms of the reactions of pyridines with carbon dioxide under reducing conditions.
ContributorsRanjan, Rajeev (Author) / Gould, Ian R (Thesis advisor) / Buttry, Daniel A (Thesis advisor) / Yarger, Jeff (Committee member) / Seo, Dong-Kyun (Committee member) / Arizona State University (Publisher)
Created2015
Description
This dissertation examines two topics of emerging interest in the field of organic geochemistry. The topic of the first portion of the dissertation is cold organic geochemistry on Saturn's moon Titan. Titan has an atmosphere and surface that are rich in organic compounds. Liquid hydrocarbons exist on the surface, most famously as lakes. Photochemical reactions produce solid organics in Titan's atmosphere, and these materials settle onto the surface. At the surface, liquids can interact with solids, and geochemical processes can occur. To better understand these processes, I developed a thermodynamic model that can be used to calculate the solubilities of gases and solids in liquid hydrocarbons at cryogenic temperatures. The model was parameterized using experimental data, and provides a good fit to the data. Application of the model to Titan reveals that the equilibrium composition of surface liquids depends on the abundance of methane in the local atmosphere. The model also indicates that solid acetylene should be quite soluble in surface liquids, which implies that acetylene-rich rocks should be susceptible to chemical erosion, and acetylene evaporites may form on Titan. In the latter half of this dissertation, I focus on hot organic geochemistry below the surface of the Earth. Organic compounds are common in sediments. Burial of sediments leads to changes in physical and chemical conditions, promoting organic reactions. An important organic reaction in subsurface environments is decarboxylation, which generates hydrocarbons and carbon dioxide from simple organic acids. Fundamental knowledge about decarboxylation is required to better understand how the organic and inorganic compositions of sediments evolve in response to changing geochemical conditions. I performed experiments with the model compound phenylacetic acid to obtain information about mechanisms of decarboxylation in hydrothermal fluids. Patterns in rates of decarboxylation of substituted phenylacetic acids point to a mechanism that proceeds through a ring-protonated zwitterion of phenylacetic acid. In contrast, substituted sodium phenylacetates exhibit a different kinetic pattern, one that is consistent with the formation of the benzyl anion as an intermediate. Results from experiments with added hydrochloric acid or sodium hydroxide, and deuterated water agree with these interpretations. Thus, speciation dictates mechanism of decarboxylation.
ContributorsGlein, Christopher R (Author) / Shock, Everett L (Thesis advisor) / Hartnett, Hilairy E (Committee member) / Zolotov, Mikhail Y (Committee member) / Williams, Lynda B (Committee member) / Gould, Ian R (Committee member) / Arizona State University (Publisher)
Created2012
Description
Organic reactions in natural hydrothermal settings have relevance toward the deep carbon cycle, petroleum formation, the ecology of deep microbial communities, and potentially the origin of life. Many reaction pathways involving organic compounds under geochemically relevant hydrothermal conditions have now been characterized, but their mechanisms, in particular those involving mineral surface catalysis, are largely unknown. The overall goal of this work is to describe these mechanisms so that predictive models of reactivity can be developed and so that applications of these reactions beyond geochemistry can be explored. The focus of this dissertation is the mechanisms of hydrothermal dehydration and catalytic hydrogenation reactions. Kinetic and structure/activity relationships show that elimination occurs mainly by the E1 mechanism for simple alcohols via homogeneous catalysis. Stereochemical probes show that hydrogenation on nickel occurs on the metal surface. By combining dehydration with and catalytic reduction, effective deoxygenation of organic structures with various functional groups such as alkenes, polyols, ketones, and carboxylic acids can be accomplished under hydrothermal conditions, using either nickel or copper-zinc alloy. These geomimetic reactions can potentially be used in biomass reduction to generate useful fuels and other high value chemicals. Through the use of earth-abundant metal catalysts, and water as the solvent, the reactions presented in this dissertation are a green alternative to current biomass deoxygenation/reduction methods, which often use exotic, rare-metal catalysts, and organic solvents.
ContributorsBockisch, Christiana (Author) / Gould, Ian R (Thesis advisor) / Hartnett, Hilairy E (Committee member) / Shock, Everett L (Committee member) / Arizona State University (Publisher)
Created2018
Description
Hydrothermal environments are important locales for carbon cycling on Earth and elsewhere in the Universe. Below its maximum temperature (~73 °C), microbial photosynthesis drives primary productivity in terrestrial hydrothermal ecosystems, which is thought to be performed by bacterial phototrophs in alkaline systems and eukaryotic algae in acidic systems, yet has received little attention at pH values intermediate to these extremes. Sequencing of 16S and 18S rRNA genes was performed at 12 hot springs with pH values 2.9-5.6 and revealed that cyanobacteria affiliated with the genus Chlorogloeopsis and algae of the order Cyanidiales coexisted at 10 of the sites. Cyanobacteria were present at pH values as low as 2.9, which challenges the paradigm of cyanobacteria being excluded below pH 4. Presence of the carotenoid β-cryptoxanthin in only 2 sites and quantitative PCR data suggest that algae were inactive at many of the sites when sampled. Spatial, but perhaps not temporal, overlap in the habitat ranges of bacterial and eukaryal microbial phototrophs indicates that the notion of a sharp transition between these lineages with respect to pH is untenable.
In sedimentary basins, biosphere-derived organic carbon is subjected to abiotic transformations under hydrothermal conditions. Benzaldehyde was experimentally evaluated as a model to assess the chemistry of aldehydes under these conditions. It was first demonstrated that gold, a traditional vessel material for hydrothermal experiments, caused catalysis of benzaldehyde degradation. Experiments in silica tubes were performed at 250, 300, and 350 °C yielding time-dependent data at several starting concentrations, which confirmed second-order kinetics. Therefore, disproportionation was expected as a major reaction pathway, but unequal yields of benzoic acid and benzyl alcohol were inconsistent with that mechanism. Consideration of other products led to development of a putative reaction scheme and the time dependencies of these products were subjected to kinetic modeling. The model was able to reproduce the observed yields of benzoic acid and benzyl alcohol, indicating that secondary reactions were responsible for the observed ratios of these products. Aldehyde disproportionation could be an unappreciated step in the formation of carboxylic acids, which along with hydrocarbons are the most common organic compounds present in natural systems.
In sedimentary basins, biosphere-derived organic carbon is subjected to abiotic transformations under hydrothermal conditions. Benzaldehyde was experimentally evaluated as a model to assess the chemistry of aldehydes under these conditions. It was first demonstrated that gold, a traditional vessel material for hydrothermal experiments, caused catalysis of benzaldehyde degradation. Experiments in silica tubes were performed at 250, 300, and 350 °C yielding time-dependent data at several starting concentrations, which confirmed second-order kinetics. Therefore, disproportionation was expected as a major reaction pathway, but unequal yields of benzoic acid and benzyl alcohol were inconsistent with that mechanism. Consideration of other products led to development of a putative reaction scheme and the time dependencies of these products were subjected to kinetic modeling. The model was able to reproduce the observed yields of benzoic acid and benzyl alcohol, indicating that secondary reactions were responsible for the observed ratios of these products. Aldehyde disproportionation could be an unappreciated step in the formation of carboxylic acids, which along with hydrocarbons are the most common organic compounds present in natural systems.
ContributorsFecteau, Kristopher Michael, 1986- (Author) / Shock, Everett L (Thesis advisor) / Gould, Ian R (Committee member) / Hartnett, Hilairy E (Committee member) / Arizona State University (Publisher)
Created2016