Confined rapid thermolysis/FTIR/ToF studies of imidazolium-based ionic liquids

Rapid scan FTIR spectroscopy and time-of-flight (ToF) mass spectrometry were utilized to study thermal decomposition of three imidazolium-based ionic liquids, with 1-ethyl-3-methyl-imidazolium (emim) as the cation, and NO₃⁻, Cl⁻, and Br⁻ as the anions. The thermal decomposition involved heating rates of 2000 K/s and temperatures to 435 °C in an ambient inert gas at 1 atm. Using sub-milligram quantities of each compound, examinations of the evolution of gas-phase species revealed that the most probable sites for proton transfer and subsequent secondary reactions were primarily the methyl group and secondarily the ethyl group. The ring appeared to remain intact, as there was no evidence of the formation of HCN, imines or related products. The most reactive compound is [emim]NO₃, since the nitrate group served as a strong oxidizer and reacted strongly with the methyl/ethyl groups at the elevated temperatures to produce common final products from combustion.