Thermal Decomposition Mechanisms of Alkylimidazolium Ionic Liquids with CN-containing Anions
AIR FORCE RESEARCH LAB EDWARDS AFB CA ROCKET PROPULSION DIV
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Due to the unusually high heats of vaporization of room-temperature ionic liquids RTILs, volatilization of RTILs through thermal decomposition and vaporization of the decomposition products can be significant. Upon heating of these RTILs in vacuum, their gaseous products were detected experimentally via tunable vacuum ultraviolet photoionization mass spectrometry performed at the Chemical Dynamics Beamline 9.0.2 at the Advanced Light Source. Experimental evidence for di- and tri-alkylimidazolium cations and nitrile containing anions indicates thermal decomposition occurs through two pathways deprotonation of the cation by the anion, and dealkylation of the imidazolium cation by the anion. Additional evidence supporting these mechanisms was obtained using thermal gravimetric analysismass spectrometry, gas chromatographymass spectrometry and temperature-jump infrared spectroscopy. In order to predict the overall thermal stability in these ionic liquids, the ability to accurately calculate both the basicity of the anions and their nucleophilicity in the ionic liquid is critical. Both gas phase and condensed phase polarizable continuum model density functional theory calculations provide support for the decomposition mechanisms and a means to determine thermal stabilities for ionic liquids in general.
- Physical Chemistry