Thermal‐ and collision‐induced dissociation studies of functionalized imidazolium‐based ionic liquid cations

Abstract

Ionic liquids are now used in applications ranging from chemical synthesis to spacecraft propulsion. With this comes the need to characterize new syntheses, identify environmental contamination, and determine eventual fate in terrestrial and space environments. This work investigates the effects of source conditions, particularly capillary temperature, on the observed mass spectrum and determines the collision‐induced dissociation (CID) patterns of imidazolium‐based ionic liquid cations as a function of their substituent types. Experiments were carried out on a Thermo LTQ‐XL ion‐trap mass spectrometer and a Bruker microTOF‐Q II mass spectrometer. Dissociation of the imidazolium cations occurred predominantly via substituent losses, except in benzyl‐substituted systems, for which the neutral loss of the imidazole was exclusively observed. Several of these dissociation pathways were studied in greater depth using complementary quantum chemical calculations. The nature of the neutral losses from the substituents was found to be highly dependent upon the nature of the substituent, as would be expected, establishing bases for characterization.

Gas-Phase Binding Energies and Dissociation Dynamics of 1-Alkyl-3-Methylimidazolium Tetrafluoroborate Ionic Liquid Clusters

“…Mass spectrometry and ion mobility spectrometry (IMS) have been powerful tools for elucidating the structure and examining the reactivity and reaction dynamics of IL clusters . Energy-resolved collision-induced dissociation (CID) experiments have been performed to elucidate the gas-phase energetics and dissociation mechanisms of aprotic and protic ILs for applications in space propulsion − and to elucidate relative affinities of various cations and anions that comprise common ILs. − IMS experiments have investigated the formation of IL clusters, IL cluster distributions and magic number clusters, and ion evaporation processes that occur during the ESI process. − For example, IL clusters of the [5C:4A] + stoichiometry exhibit high stability, that is, magic number clusters, for at least two ILs. , Further, in addition to single ion-pair losses (C:A) upon dissociation, simultaneous loss of clusters involving multiple ion pairs, (C:A) n , has been reported for select IL clusters. , …”

Absolute Trends and Accurate and Precise Gas-Phase Binding Energies of 1-Alkyl-3-Methylimidazolium Tetrafluoroborate Ionic Liquid Clusters from Combined Independent and Competitive TCID Measurements

“…The importance of elucidating absolute and relative trends in the structure, energetics, and reactivity of chemical systems has long been appreciated and has led to the development of absolute and relative cation and anion affinity scales for a wide variety of neutral and ionic systems. − In particular, ESI tandem MS (ESI-MS/MS) approaches typically using collisional activation have been employed to examine the dissociation of IL clusters to establish cation–anion interaction scales for ILs. − Several studies have examined the variable-energy CID behavior of cationic and anionic clusters of various ILs as a function of collision energy. In contrast to the threshold CID approach employed in our work, where energetic information is extracted at the onset of dissociation, these studies were based on comparisons at 50% dissociation.…”