Date of Award
Summer 8-15-2015
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Electrochemistry provides a versatile method for a variety of synthetic transformations. It has been used in the Moeller lab to generate reactive intermediates to trigger intramolecular cyclization reactions, recycle chemical oxidants on microelectrode arrays, and to study binding interactions of molecules attached to the arrays with biological receptors in solution. Electrochemical techniques have also been demonstrated as a green chemical alternative to many traditional processes. While organic electrochemistry has been widely accepted by the electrochemical community, the synthetic chemistry community has failed to fully appreciate its utility. The goal of this thesis is to demonstrate the versatility and scope of electrochemical techniques from the femtomolar to preparative scale and to emphasize electrochemistry as a sustainable process.
First, a series of electrochemically mediated chemical oxidations was explored. Since the selectivity of a chemical oxidant is not always based on oxidation potential and can be influenced by chirality, chelation, and other factors, electrochemical mediated oxidations are an important tool for organic synthesis. In addition, traditional stoichiometric metal oxidants generate a stoichiometric reduction metal waste product that can be avoided in an electrochemically mediated oxidation reaction. The chemical oxidants were recycled on a microelectrode array to functionalize the polymer surface and then scaled to the preparative scale. In doing so, chemical oxidation reactions were performed in an environmentally benign, sustainable manner. On the preparative scale, the electricity used to power the mediated oxidation reactions was supplied by a photovoltaic cell. This was done to emphasize that for electrochemistry to be a green alternative to traditional oxidation methods, it requires a green source of electricity. For electrochemical oxidations to be sustainable the whole process must be considered and that includes the source of the electricity consumed.
In a similar vein, the origins of the chemicals used in any electrolysis reaction must be evaluated. Chemicals obtained from biorenewable resources would be an ideal alternative to chemicals derived from petroleum feedstocks. Towards that effort, lignin disassembly to small aromatic monomers was explored. Under solvolytic conditions, raw sawdust could be converted to electron-rich aromatic aldehyde- and cinammyl- monomers. These monomers were then electrochemically processed into synthetic precursors, and their synthetic utility is currently being further studied.
Finally, the energy demands and economics of an electrochemical process were investigated. Every electrochemical oxidation is by nature paired with an electrochemical reduction. Only considering the oxidative half reaction is thereby energetically wasteful. For a more efficient electrochemical process, the anodic oxidation reaction must be paired with a useful cathodic reduction reaction. In preliminary studies, the oxidation of lignin-derived substrates was paired with H2 production for in situ generation of H2 for hydrogenation reactions. Currently, the paired electrochemical reduction of CO2 to CO is being explored for use in hydroformylation reactions. In this manner, chemical reagents can be generated on site thus bypassing the costs associated with shipping and storage.
Language
English (en)
Chair and Committee
Kevin D Moeller
Committee Members
Vladimir Birman, Garland Marshall, Liviu Mirica, John-Stephen Taylor,
Recommended Citation
Nguyen, Bichlien H., "Towards Sustainable Electrochemistry: Applications from Femtomolar to Preparative Scale" (2015). Arts & Sciences Electronic Theses and Dissertations. 529.
https://openscholarship.wustl.edu/art_sci_etds/529
Comments
Permanent URL: https://doi.org/10.7936/K7JW8C33