I Studies on the Reactivity of a Bis–Mesityl Imidazolyl Carbene Intermediate Toward Carbon Dioxide and Stability of the Result
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i Studies on the Reactivity of a Bis–Mesityl Imidazolyl Carbene Intermediate toward Carbon Dioxide and Stability of the Resulting Carboxylate By Seon Young Ka Submitted in Partial Fulfillment of the Requirements For the Degree of Master of Science In the Chemistry Program YOUNGSTOWN STATE UNIVERSITY August, 2019 ii Studies on the Reactivity of a Bis–Mesityl Imidazolyl Carbene Intermediate with Carbon Dioxide and the Stability Characterization after Carbon Dioxide Adduction Seon Young Ka I hereby release this thesis to the public. I understand that this thesis will be made available from the OhioLINK ETD Center and the Maag Library Circulation Desk for public access. I also authorize the University or other individuals to make copies of this thesis as needed for scholarly research. Signature: Seon Young Ka, Student Date Approvals: Clovis A. Linkous, Thesis Advisor Date John A. Jackson, Committee Member Date Michael A. Serra, Committee Member Date Dr. Salvatore A. Sanders, Dean of Graduate Studies Date ABSTRACT 1,3–bis(2,4,6–trimethylphenyl)imidazolium carboxylate, an adduct between CO2 and the N–heterocyclic carbene (NHC), 1,3–bis(2,4,6–trimethylphenyl)–1,3–dihydro–2H– imidazol–2–ylidene, was synthesized to study the reactivity of CO2 after binding to the carbene intermediate. Nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, X–ray powder diffraction (XRD), gas chromatography (GC) and thermal gravimetric analysis (TGA) were employed to characterize the final imidazolium carboxylate. GC was specifically used to study the dissociation of the CO2 adduct. The structure of the synthesized zwitterion was confirmed via 1H and 13C NMR, where adduct formation generated a new peak in the 13C NMR spectrum. IR spectroscopic data showed –1 a significant characteristic peak for C=O stretch at around 1670 cm . TGA spectra showed that the zwitterion‟s weight loss of 13% at 155 °C which is the percent weight of CO2. The GC study of CO2, which was released after treating the imidazolium carboxylate with 5% H2O in CH3CN, enabled the possibility of the reversibility of CO2– NHC adduct formation. The stability and air sensitivity of the imidazolium carboxylate were tested in polar, nonpolar, acidic, basic, and mixed solvents via simple effervescence tests and GC. The hydrolytic stability of the imidazolium carboxylate was examined. The bis-mesityl carboxylate showed reasonable stability in water, in contrast to carboxylates with smaller alkyl substituents, but admixture with organic solvent would cause it to break down into the corresponding imidazolium bicarbonate. After exposure to H2 (g) and heat, there was evidence for the reductive conversion of the carboxylate into imidazolium formate. This suggests the application of the mesityl imidazolyl carbene as an organic catalyst for CO2 reduction. iii ACKNOWLEDGEMENTS First and foremost, I thank and praise my Lord, our Father in Heaven, the Almighty, for all His blessings to complete my research work. I extend my sincere gratitude to my research advisor Dr. Clovis A. Linkous for letting me be a part of his research group. I thank him for his tremendous and constant amount of advice as a chemist. I also thank Dr. John A. Jackson and Dr. Michael A. Serra for their commitment to being on my committee members and their guidance to complete this degree. I thank Dr. John A. Jackson for providing comments and suggestions on solubility experiments. I would like to thank Dr. Michael A. Serra for continuously encouraging me to work harder. I thank my mentor Dr. Sherri R. Lovelace-Cameron for her continuous support and inspiration to confer my degree. The YSU Chemistry Department faculty and staff have granted me the opportunity to conduct my research. I especially thank Mr. Ray Hoff for analytical technique as sistance and Ms. Lisa Devore for her continuous encouragement. They have made the journey more precious and memorable. I cannot thank enough my husband Eddie Cho for his confidence in me. His advocacy turned my life, so I could pursue and complete my degree. I would have not made it this far without the love and uplifting messages from my family and in-laws. Thank you so much. iv For Rudy, My joy, my heart, my baby v TABLE OF CONTENTS Abstract .............................................................................................................................. iii Acknowledgements ............................................................................................................ iv Table of Contents ............................................................................................................... vi List of Figures .................................................................................................................... ix List of Tables ..................................................................................................................... xi List of Equations ............................................................................................................... xii List of Abbreviations ........................................................................................................ xii Chapter 1: Introduction ....................................................................................................... 1 Background ................................................................................................................... 1 NHCs and Their Applications and Publications ........................................................... 9 Statement of Purpose .................................................................................................. 16 Chapter 2: Materials and Methods .................................................................................... 19 Materials ..................................................................................................................... 19 Preparing the Reagents ............................................................................................... 20 Characterization Techniques ....................................................................................... 22 Nuclear Magnetic Resonance (NMR) Analysis .................................................... 22 Infrared (IR) Spectroscopy Analysis .................................................................... 22 Thermogravimetric Analysis (TGA) .................................................................... 22 Gas Chromatography (GC) Analysis .................................................................... 23 Powder X–Ray Diffraction (XRD) Analysis ........................................................ 23 Effervescence Test Techniques ............................................................................ 24 Solubility Test Techniques ................................................................................... 25 vi Chapter 3: Results and Analysis ....................................................................................... 26 1,3–bis(2,4,6–trimethylphenyl)–1,3–dihydro–2H–imidazole–2–ylidene ................... 26 NMR Characterization and Analysis .................................................................... 26 IR Analysis ........................................................................................................... 29 Synthesis of 1,3–bis(2,4,6–trimethylphenyl)imidazol–2–carboxylate (3) .................. 30 Characterization of 1,3-bis(2,4,6-trimethylphenyl)imidazolium-2-carboxylate (3a) . 32 NMR Characterization and Analysis .................................................................... 32 IR Characterization and Analysis ......................................................................... 37 TGA Study ............................................................................................................ 38 Study of Carbonyl Carbon from IMesCO2 (3a) via Effervescence Test .............. 39 Study of Carbonyl Carbon Dissociated from IMesCO2 (3a) via GC Analysis .... 43 Single Crystal Structure Analysis Preparation of IMesCO2 (3a) ......................... 47 Powder X–ray Diffraction Study of IMesCO2 (3a) .............................................. 51 Dry Air Stability Characterization of IMesCO2 ( 3b) .................................................. 52 NMR Characterization .......................................................................................... 52 IR Characterization ............................................................................................... 56 TGA Study ............................................................................................................ 57 Study of Carbonyl Carbon Released from IMesCO2 ( 3b) via GC ....................... 59 Study of Carbonyl Carbon Released from IMesCO2 (3b) via Effervescence Test60 Single Crystal Structure Analysis Preparation of IMesCO2 ( 3b) ......................... 61 Water Stability Characterization of 3b (4) .................................................................. 63 NMR Characterization .......................................................................................... 63 Hydrogen Gas Stability Characterization of 3b (5) .................................................... 69 vii NMR Characterization .......................................................................................... 69 Effervescence Test and Single Crystal Structure Analysis of 5 ........................... 75 Heat Resistance and Stability Characterization of 5 ..................................................