Microwave-assisted Synthesis of 1-(perfluorohexyl)-3-methylimidazolium iodide
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.484
Microwave-assisted Synthesis of 1-(perfluorohexyl)3-methylimidazolium iodide James E. Knoop and Jeffrey R. Alston Joint School of Nanoscience and Nanoengineering, North Carolina Agricultural and Technical State University, Greensboro, NC, 27401, USA
ABSTRACT
A perfluorinated ionic liquid, 1-(perfluorohexyl)-3-methylimidazolium iodide, was synthesized via microwave reaction and compared to a non-fluorinated analog. Typically, the synthesis of fluorinated ionic liquids involves long reaction times and multiple steps. We have demonstrated a shortened synthesis and a more straightforward procedure, by using a microwave reactor for the microwave-assisted synthesis of 1-(perfluorohexyl)-3methylimidazolium iodide. The addition of fluorinated alkyl chains on imidazolium ionic liquid cations increases the molecular free volume of the ionic liquid which is beneficial for increasing CO2 physisorption. Computational and experimental data shows an increased CO2 solubility and capacity for fluorinated ionic liquids. The perfluoroalkyl functionalized ionic liquid is characterized using 1H and 19F NMR spectroscopy, FTIR spectroscopy, and DSC. By DSC, a crystallization onset is near -31 ℃ and while the onset of the melting point between 30 and -17 ℃.
INTRODUCTION: Imidazolium-based ionic liquids (ILs) are useful compounds for physically adsorbing CO2. This was discovered by Blanchard et al. when searching for a method to extract naphthalene from [BMIm][PF6] using CO2 [1]. Moreover, ILs have unique properties such as high thermal stability and low vapor pressure. They are electrically conducting, have excellent transport properties, and can be insoluble in many organic solvents or water. Since 1999, there have been over 340+ articles reported on ILs investigated for CO2 adsorption with over 282 reports in the last 10 years. Recently, fluorinating IL substituents was identified as a pathway to increase the CO2 adsorption capacity of ILs. A recent review was published that compares experimental gas solubility
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values with molecular simulation trends [2]. The review highlights the affinity between fluoroalkyl moieties and CO2 molecules. Typically, ILs with fluoroalkyl-functionalized anions have the highest CO2 adsorption capacity. There are many mechanisms reported that describe the solubility of CO2 in ILs, the most common of which are the anion effect and free volume effect. The anion effect suggests that CO2 solubility is more strongly affected by the anion than the cation; however, this does not fully explain trends reported experimentally [3, 4]. Alternatively, the free volume effect presents a mechanism that more accurately describes observed CO2 adsorption trends, stating that increases in molecular free volume in th
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