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Tetraalkylammonium Chlorides as Melting Point Depressants of Ionic Liquids

Publication . Martins, Mónia A. R.; Abranches, Dinis O.; Silva, Liliana P.; Pinho, Simão; Coutinho, João A.P.

With the (re)advent of eutectic mixtures within the field of deep eutectic solvents, special attention has been given to the measurement of solid–liquid equilibrium (SLE) phase diagrams, supported by the relevant information they can provide on the molecular interactions and melting temperature depression of any given system. As such, this work investigates the SLE phase diagrams of mixtures between ionic liquids and tetraalkylammonium chlorides (methyl, ethyl, and propyl), with the goal of decreasing the melting temperature of ionic liquids and ammonium salts, thus, expanding their application scope. Results show that tetraalkylammonium salts exhibit negative deviations from thermodynamic ideality when mixed with ionic liquids, which are increased by increasing their alkyl chain length and are interpreted in terms of anion exchange mechanisms. In turn, this nonideality contributes greatly to depression of the melting point of the ionic liquids examined. Overall, this work demonstrates that the correct combination of tetraalkylammonium/ILs anions and cations can lead to significant melting point depressions in both species, thus creating new ionic liquid mixtures using an approach akin to that used to form deep eutectic solvents.

2023Journal article

Open access