Electrochemical Oxidation Of Lignin For The Production Of Value Added Chemicals

Author : Shannon L. Goes
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (138 download)

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Download or read book Mediated Electroorganic Oxidations written by Shannon L. Goes and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Electroorganic oxidation reactions are appealing because protons, rather than undesirable stoichiometric chemicals, act as the terminal oxidant. Direct electrochemical oxidation of an organic molecule generates a high-energy radical cation. The high potentials required to produce these species frequently cause decomposition of reagents and/or reactions with ancillary functional groups. Proton-coupled electron-transfer (PCET) mediators are a specialized class of organic molecules that undergo facile electron transfer at an electrode to generate an active oxidant that subsequently removes at least one electron and one proton from substrate. This mediated strategy bypasses the formation of high-energy intermediates, thereby reducing the electrode potentials needed for analogous direct electrolysis reactions.The first part of this thesis serves as an introduction to electrochemistry and mediated electrosynthesis. In Chapter 1, mediated electrosynthesis is broadly described for a general audience. Specific examples from my research are used to showcase the chemoselectivity afforded by PCET electrochemical mediators. In Chapter 2, an undergraduate laboratory exercise based on a classic electrochemical reaction, the Shono oxidation, is explained. The experiments in this lab demonstrate that direct electrochemical oxidation of amines is not compatible with electron-rich functional groups. In Chapter 3, the exploration of aminoxyl-mediated 2e-/H+ hydride transfer mechanism and quantification of electrocatalytic rates forms the basis for an undergraduate laboratory exercise. The second part of this thesis presents a study of mediated electrolysis for enabling organic synthesis. In Chapter 4, electrochemical aminoxyl-mediated oxidation of secondary piperidines is employed to generate pharmaceutically-relevant Îł-cyanopiperidines. Use of an aminoxyl hydride-transfer mediator allows the reactions to proceed at low applied potentials, thereby enabling broad functional group tolerance. In Chapter 5, strategies for the oxidation of lignin, a complex polymer found in non-edible biomass, and subsequent depolymerization to valuable aromatic chemicals are summarized. In Chapter 6, the stability and oxidative driving force for a series of electrochemical e-/H+ hydrogen atom transfer radical mediators are evaluated. The long lifetimes and selectivity for secondary benzylic alcohol oxidation, even in the presence of sugars, indicate that oximes are well-suited to oxidative conversion of heterogeneous biomass. In Chapter 7, oxime-mediated oxidation of lignin facilitates the conversion of biomass to high-quality polysaccharides and promising yields of aromatic chemicals. The stability of the electrogenerated radical enables the reaction to be conducted off-electrode using scalable and sustainable electrochemical flow reactor technologies.