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Mechanistic and Computational Studies of Ferroin, Simple Organic Acids, and Bromine Oxides

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Mechanistic and Computational Studies of Ferroin, Simple Organic Acids, and Bromine Oxides Mechanistic and Computational Studies of Ferroin, Simple Organic Acids, and Bromine Oxides Elucidating the Complex Electrochemical Dance in an Oscillating Reaction A thesis presented to Faculty of the Graduate School of Chemistry At the University of Missouri-Columbia In partial fulfillment of the requirements for the degree of Master of Science By: Cory Camasta Dr. Rainer Glaser, Ph.D., Thesis Supervisor December 2016 The undersigned, appointed by the Dean of the Graduate School, have examined the thesis entitled: MECHANISTIC AND COMPUTATIONAL STUDIES OF FERROIN, SIMPLE ORGANIC ACIDS, AND BROMINE OXIDES presented by Cory Camasta, a candidate for the Master of Science degree, and hereby certify that, in their opinion, it is worthy of acceptance. _______________________________ Dr. Rainer E. Glaser _______________________________ Dr. Thomas D. Sewell _______________________________ Dr. Aigen Li Acknowledgement The scientist’s journey is a long and challenging one. Though I do not know where mine will end, I have high hopes for it. In this short preface to the work that has directly consumed a large amount of my last nine months at the University of Missouri (and indirectly quite a bit longer), I would like to take a moment to give due thanks: Thank you to all of the dedicated researchers that allowed me to write this thesis without ever putting on a pair of protective eyewear – including the one that gave me a job. Thank you to those who loved every second of the research you did. Your sincere efforts to extend our collective knowledgebase certainly show in the fruits of your labor. Thank you to those who hated every second of the research you did. Even though you may have thought so at the time, your struggles were not all in vain. I hope they taught you something useful and that you find your way onto the path that you deserve to follow. Thank you to those who have shown me love and acceptance, both in academia and in the real world. It is for you that I am motivated to better myself and, by doing so, better the world. I am grateful to have received some of your light and hope to find more people like you in the next leg of my journey. Thank you to those who have shown me the ugly side of academia. I know a lot more now than I once knew (despite also feeling that smaller-fraction-of-everything-that-exists thing), and will use what you have taught me to become a wiser and all-around better human being. Even so, I hope to avoid people like you in the next leg of my journey. For better or for worse, our lives are constantly impacted by different people and new things. Instead of letting the evil in the world consume us, as it is so easy to do sometimes, please join me now if you have not already in this quest to turn copper to orichalcum, coal to carbene, and eventually turn lead to gold. It is time to science! ii Table of Contents ii. Acknowledgement iv. List of Figures, Schemes, Tables and Equations v. List of Abbreviations 1. Introduction ............................................................................................................................................... iv 1.1 Abridged History of Belousov and Zhabotinsky’s Reaction ....................................................................... 3 1.2 Components and General Mechanisms of a BZ Reaction .......................................................................... 5 1.2.1 Metal .................................................................................................................................................... 5 1.2.2 Reducing Agent .................................................................................................................................... 7 1.2.3 Halogen Oxides and Strong Acid ......................................................................................................... 8 1.3 Ferrum and Ferroin ................................................................................................................................... 10 2. Materials & Methods ................................................................................................................................. 12 2.1 Theory ........................................................................................................................................................ 18 2.2 Calibrating the System .............................................................................................................................. 21 2.3 The Importance of Phase .......................................................................................................................... 27 3. Results ....................................................................................................................................................... 29 3.1 The Arrow of Time ..................................................................................................................................... 29 3.2 Proposed Mechanisms .............................................................................................................................. 32 3.2.1 The Induction Period and Rise of Oscillations .................................................................................. 32 3.2.2 Propagation via One-Electron Oxidations......................................................................................... 38 3.2.3 Termination via Two-Electron Oxidations ........................................................................................ 41 3.2.4 Products of a BZ Reaction.................................................................................................................. 44 3.2.5 Elusive Intermediate: Bromotartronic Acid ...................................................................................... 49 3.3 Metal Catalysis .......................................................................................................................................... 51 3.3.1 Evidence for the Outer-Sphere Electron Transfer ............................................................................ 51 3.3.2 Tautomerizations ............................................................................................................................... 56 3.4 Modeling the Metal Catalysis ................................................................................................................... 60 3.4.1 First Attempts .................................................................................................................................... 60 3.4.2 Ligand Field Analysis .......................................................................................................................... 61 3.4.3 Ligand Fields in Another Practical Model ......................................................................................... 65 3.5 Bromine Oxide/Oxoacid Equilibria ........................................................................................................... 67 3.5.1 What is Known ................................................................................................................................... 67 3.5.2 What is Less Known ........................................................................................................................... 68 3.5.3 What We Can Speculate – Brozone and Bonding ............................................................................. 76 3.6 Fruits of Labor ........................................................................................................................................... 80 4. Discussion .................................................................................................................................................. 86 4.1 Potential Flaws, Fixes, and Side Notes ..................................................................................................... 86 4.2 Conclusions and Future Direction ............................................................................................................. 89 iii List of Figures, Schemes, Tables and Equations 79 81 Figure 1. Morse potential plot for Br— Br ............................................................................................... 15 Figure 2. Aqueous optimized structures of bromine-free derivatives of malonic acid ................................ 35 Figure 3. Aqueous optimized structures of brominated derivatives of malonic acid .................................. 37 Figure 4. Radical recombination products and subsequent decompositions. ............................................. 45 Figure 5. Aqueous optimized structure of hypothetical ferriin-bromomalonic acid adduct ....................... 48 Figure 6. Additional theorized intermediates and byproducts of a BZ reaction .......................................... 50 Figure 7. Spin density isosurfaces of malonic and bromomalonic acids and neutral radicals ..................... 58 Figure 8. Molecular orbital bonding schemes of iron in the context of ligand field theory ......................... 63 Figure 9. Aqueous optimized structures of assorted singlet (S=0) bromine oxides ..................................... 72 Figure 10. Electrostatic potential of BrOOOOOBr ......................................................................................... 75 Figure 11. Oxidation of BrOBr by acidic bromate......................................................................................... 77 Figure 12. Acid-mediated condensation of bromate and bromous acids
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