Reactivity of Ionic Liquids: Studies on Thermal Decomposition Behavior of 1-Butyl-3-methylimidazolium Tetrafluoroborate

The Ionic Liquid 1-butyl-3-methylimidazolium tetrafluoroborate [C(4)C(1)im]BF4 serves as a commonly solvent in inorganic material synthesis and analytics. Nevertheless, its application is frequently associated with trial and error approaches. Thereupon, detailed knowledge on the thermal behavior is the key information for understanding the reactivity of [C(4)C(1)im]BF4. 1-butyl-3-methylimidazolium tetrafluoroborate behaves as a glass in the cold, its glass transition temperature being theta(g) = -83 degrees C. During heating with 10 K.min(-1) [C(4)C(1)im]BF4 appears to be stable above 350 degrees C with onset temperatures theta(onset, DSC )= 375 degrees C, theta(onset), (DTG )= 422 degrees C, and (theta onset), (TG) = 437 degrees C. Thereby, thermal decomposition occurs in a single step reaction forming 1-methyl-1H-imidazole (CH3C3H3N2 or C4H6N2), but-l-ene (C4H8), fluoromethane (CH3F) and boron trifluoride (BF3) as main species, as determined by thermogravimetry coupled with mass spectrometry and FTIR spectroscopy. To be more specific in thermal behavior, the temperature and time dependent stability is evaluated here on the basis of the kinetic model of maximum operation temperature - MOT. Clearly, thermal stability rises with application time, thus being 193 degrees C for one hour, while reaching only 141 degrees C for one day, and 114 degrees C for one week. The incipient decomposition (<= 1 %) at the calculated time dependent maximum operation temperature finally is verified by optical analysis, infrared (IR), and nuclear magnetic resonance (NMR) spectroscopy.