Insights into the Stabilization of Fluoride Ions in Ionic Liquids: Pointers to Better Fluorinating Agents

Abstract

The fluorination efficiency of a fluorinating agent depends on the free availability of the fluoride ions, which in turn depends on its interaction with its solvation shell. A stable fluoridebased poor solvate ionic liquid (SIL) comprising 1-ethyl-3methylimidazolium (EMIM) cation and ethylene glycol (EG) was recently reported and demonstrated as a fluorinating agent. Herein, we performed ab initio calculations and ab initio molecular dynamics simulations to gain a microscopic understanding of the intermolecular interactions in this SIL in gas, liquid, and crystalline phases. Ethylene glycol (EG), being capable of forming hydrogen bond(s) with the fluoride ion, prevents the latter from reacting with the EMIM cation. Fluoride forms hydrogen bonds with both the cation and the EG molecule, but it was found to have more affinity toward EG, forming a stronger hydrogen bond with its hydroxyl proton than with the acidic proton of the cation. An optimal concentration of EG in the SIL balances its contribution to stabilizing the fluoride ion and yet making fluoride available for fluorination.

Fluoride Ion in Alcohols: Isopropanol vs Hexafluoroisopropanol

“…The interaction energy calculations revealed that HFIP encapsulated stronger interactions with F – than the IP alcohol in structural mechanisms that involved changes in the HFIP conformations. In this context, the use of tert -butyl alcohol would be interesting to further pursue this direction as suggested for the previous work on [1-ethyl-3-methylimidazolium]­F-alcohol complexes . The strong OH···F – interaction in the CsF–HFIP system is further validated by the peak shifts observed in the IR and 1 H NMR spectra and the decrease in the activity coefficients of the HFIP alcohols upon the addition of CsF.…”

“…In this context, the use of tert-butyl alcohol would be interesting to further pursue this direction as suggested for the previous work on [1-ethyl-3methylimidazolium]F-alcohol complexes. 62 The strong OH••• F − interaction in the CsF−HFIP system is further validated by the peak shifts observed in the IR and 1 H NMR spectra and the decrease in the activity coefficients of the HFIP alcohols upon the addition of CsF. The strengthened interaction between the OH and F − , which is ascribed to the introduction of the fluoroalkyl group, is rationalized to facilitate the dissociation of the cation and anion in the CsF−HFIP system, engendering the enhanced ionic conductivity observed in the diffusion coefficient measurements.…”

Mechanically Induced Nanoscale Architecture Endows a Titanium Carbide MXene Electrode with Integrated High Areal and Volumetric Capacitance

“…It is also worth noting that the etching kinetics is strongly influenced by the nature of reaction media; for instance, employing [C 2 mim]NTf 2 or [C 4 mim]PF 6 as the solvent normally results in the incomplete conversion of the MAX phase, which may originate from the difference in the solvation of active etching species or products (Figures S31 and S33, Supporting Information). [ 28 ]…”

Fluoride Anions: Unexploited but Effective Halogen Bond Acceptors

“…The adopted experimental conditions are quite simple and expectedly can be employed easily for other substrates. Several other cocrystals wherein fluoride anion is the HaB acceptor may become available; it will thus become possible to investigate the specific features of fluoride anion in halogen bonded self‐assembled systems and to explore the applicative usefulness of halogen bonded cocrystals containing fluoride anions, e. g., as nucleophilic fluorinating agents [16] …”