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Syntheses of Aluminum Amidotrihydroborate Compounds and Ammonia Triborane As Potential Hydrogen Storage Materials

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Syntheses of Aluminum Amidotrihydroborate Compounds and Ammonia Triborane As Potential Hydrogen Storage Materials Syntheses of Aluminum Amidotrihydroborate Compounds and Ammonia Triborane as Potential Hydrogen Storage Materials THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Jason Michael Hoy Graduate Program in Chemistry The Ohio State University 2010 Master's Examination Committee: Dr. Sheldon G. Shore, Advisor Dr. James A. Cowan Copyright by Jason Michael Hoy 2010 Abstract A number of methods and materials have been synthesized for use as hydrogen storage materials. However, to date, none of the materials are capable of being used as a sustainable fuel source as a result of poor recyclability. Therefore, new materials need to be synthesized and evaluated in order to obtain the goal of creating a hydrogen fuel economy. Furthermore, some possible hydrogen storage candidates have been ignored as a result of poor and laborious syntheses. Finding new synthetic routes to these materials opens exploration of their effectiveness as a hydrogen source. The reaction of lithium aluminum hydride with ammonia borane has been investigated in varying ratios. Evaluation of the hydrogen released, proton and boron-11 NMR spectroscopy, and infrared spectroscopy indicate the formation of a compound of composition LiAl(NHBH3)H2 in the equimolar reaction of lithium aluminum hydride and ammonia borane followed by subsequent addition of amidotrihydroborate to this material with the presence of additional ammonia borane to form LiAl(NHBH3)(NH2BH3)H and LiAl(NHBH3)(NH2BH3)2. It was unclear whether the reaction in a ratio of 1:4 lithium aluminum hydride to ammonia borane produced LiAl(NH2BH3)4 or if the product was identical to that of the reaction in a 1:3 ratio. All of the compounds made retain a high gravimetric capacity of hydrogen. Solvent-free sodium octahydrotriborate was synthesized via a new method en route to ammonia triborane. Tetrahydrofuran borane complex solution was stirred with an amalgamation of sodium and mercury to produce the solvent coordinated sodium octahydrotriborate and sodium ii borohydride. The product was separated by extraction with ethyl ether and heating to remove coordinated solvent. Average yield of the final product was approximately 60%. A literature method for synthesizing ammonia triborane was refined, removing the need for multiple cooling steps and for the use of column chromatography to purify the product. The reaction of elemental iodine with tetrabutylammonium octahydrotriborate was allowed to react at room temperature rather than addition at low temperatures, producing identical results to the literature procedure. Furthermore, the ammonia triborane was separated from the remaining residue after removal of the solvent using a mixed solvent of hexanes and ethyl ether. Potassium octahydrotriborate was also able to be used in the synthesis in place of the tetrabutylammonium salt. iii Dedication This document is dedicated to my wife, Julia. Without her continued support throughout my graduate career, I would have long ago forgotten what is important in life. iv Acknowledgments I am thankful to Dr. Sheldon Shore for providing his support and knowledge during my graduate career at Ohio State University. Dr. Shore provided me with advice and insight into my research I would not have thought about personally. I also thank the Shore Group members for providing their daily support and understanding. In particular, I thank Dr. Matthew R. Sturgeon for all of his technical advice and Chris Potratz for his help with attempts at X-ray diffraction and crystallography. I also would like to thank Dr. J.-C. Zhao in the Department of Materials Science and Engineering for his monetary and educational support. Furthermore, I would like to thank the Zhao Group members for their perspective of my research from a materials science approach. v Vita June 2002 ............................................................. Twin Valley South High School 2006 ..................................................................... B.S. Chemistry, Ohio University 2006 to 2008 ....................................................... Graduate Teaching Associate, Department of Chemistry, The Ohio State University 2008 to present …………………………….. Graduate Research Assistant, Department of Materials Science and Engineering, The Ohio State University Fields of Study Major Field: Chemistry vi Table of Contents Abstract...............................................................................................................................ii Dedication...........................................................................................................................iv Acknowledgments...............................................................................................................v Vita.....................................................................................................................................vi Table of Contents..............................................................................................................vii List of Tables......................................................................................................................xi List of Figures....................................................................................................................xii List of Abbreviations........................................................................................................xiii Chapter 1: Introduction ...................................................................................................... 1 1.1 Chemical Hydrogen Storage .............................................................................. 1 1.2 Ammonia Borane and the Amidortrihydroborate Anion ................................... 4 1.2.1 Ammonia Borane ................................................................................ 4 1.2.2 Amidotrihydroborate ........................................................................... 5 1.2.3 Structures of Amidotrihydroborate Compounds ................................. 9 1.2.4 Use of Lithium Amidotrihydroborate in Reduction Reactions ......... 10 vii 1.2.5 Use of Ammonia Borane and Amidotrihydroborate as a Hydrogen Fuel Source ................................................................................................. 10 1.2.6 Regeneration of Ammonia Borane .................................................... 13 1.3 Ammonia Triborane ......................................................................................... 15 1.3.1 The Octahydrotriborate Anion .......................................................... 15 1.3.2 Syntheses of Ammonia Triborane ..................................................... 17 1.3.3 Reactivity of Ammonia Triborane .................................................... 18 1.4 Statement of the Problem ................................................................................. 18 Chapter 2: Results and Discussion.....................................................................................21 2.1 Lithium Aluminum Hydride Reactions with Ammonia Borane ...................... 21 2.1.1 Rationale for the Aluminum Amidotrihydroborate Compounds ...... 21 2.1.2 Equimolar Reaction of Lithium Aluminum Hydride and Ammonia Borane ........................................................................................................ 21 2.1.3 The Reaction of Lithium Aluminum Hydride and Ammonia Borane in a 1:2 Ratio .............................................................................................. 22 2.1.4 The Reaction of Lithium Aluminum Hydride and Ammonia Borane in a 1:3 Ratio .............................................................................................. 24 2.1.5 The Reaction of Lithium Aluminum Hydride and Ammonia Borane in a 1:4 Ratio .............................................................................................. 25 2.1.6 Discussion of the Results of the Reactions of LiAlH4 and H3NBH3 . 27 viii 2.2 Solvent-Free Sodium Octahydrotriborate ........................................................ 46 2.3 Ammonia Triborane ......................................................................................... 50 2.3.1 Improved Synthesis of Ammonia Triborane ..................................... 50 2.3.2 The Reaction of KB3H8 with I2 ......................................................... 51 2.3.3 The Reaction of Ammonia Triborane with Sodium Hydride ............ 51 Chapter 3: Experimental ................................................................................................... 53 3.1 Equipment and Apparatus ................................................................................ 53 3.1.1 Nuclear Magnetic Resonance Spectroscopy (NMR) ......................... 53 3.1.2 X-Ray Powder Diffraction ................................................................ 53 3.1.3 Infrared Spectroscopy ........................................................................ 53 3.1.4 Vacuum Line ..................................................................................... 54 3.1.5 Glassware .......................................................................................... 55 3.1.6 Dry Box ............................................................................................. 56 3.2 Solvents and Reagents ...................................................................................... 57 3.2.1 Solvents ............................................................................................
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