Quantitative Research on the Vaporization and Decomposition of [EMIM][Tf2N] by Thermogravimetric Analysis–Mass Spectrometry

The thermal stability of [EMIM][Tf2N] was investigated by thermogravimetric analysis–mass spectrometry (TG–MS) in this study. It showed that [EMIM][Tf2N] decomposed at temperatures over 350 °C by Hoffman elimination and substitution of nucleophilic mechanisms (SN, including the unimolecular substitution nucleophilic reaction SN1 and the bimolecular substitution nucleophilic reaction SN2). The instability of [EMIM][Tf2N] is induced by decomposition of the anion [Tf2N] to a more nucleophilic group, such as NH2 and F, and then methyl and/or ethyl in the imidazolium cation are attacked by those groups of relatively high nucleophilic activity. Mass loss of [EMIM][Tf2N] in a nitrogen atmosphere can be attributed to its decomposition and/or vaporization. The ratios of decomposition and vaporization (Dec/Vap), elimination and SN (Elim/SN), and SN2/SN1 for [EMIM][Tf2N] were approximately determined by TG–MS. The thermal stability including both decomposition and vaporization of [EMIM][Tf2N] decreases with an increase of the temperature, while decomposition is more sensitive to the temperature than evaporation. Vaporization of [EMIM][Tf2N] dominates the mass loss at temperatures below 350 °C, while decomposition dominates the mass loss at temperatures over 350 °C.