(220d) Reaction Ensemble Monte Carlo Simulations of Protic Ionic Liquid Formation

AH + B → [A^—] [BH⁺]

and the mixture, by convention, has a melting point below 100 °C. The ionization of an acid-base pair is difficult to predict. The difference between the aqueous pK_a of the acid and that of the base has shown some correlation with the boiling point of the mixture [1]. However, when paired with the same acid, bases with similar pK_as may exhibit very different ionic conductivities [2].

Reaction ensemble Monte Carlo is one promising method to predict which acid-base pairs form PILs. The challenge lies in developing Monte Carlo moves that efficiently insert and delete charged species into an ionic liquid environment. Simple insertions, semi-grand insertions [3], and state-of-the-art continuous fraction component (CFC) insertions all fail at such a task. We present a combination semi-grand/CFC move that succeeds and demonstrate its effectiveness on ethylammonium nitrate and a series of bases paired with acetic acid.

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Document release number LLNL-ABS-749853.

References

1. Yoshizawa, W. Xu and C. A. Angell, “Ionic Liquids by Proton Transfer: Vapor Pressure, Conductivity, and the Relevance of ΔpK_a from Aqueous Solutions”, J. Am. Chem. Soc., 2003, 15411-15419
2. Stoimenovski, E. I. Izgorodina and D. R. MacFarlane, “Ionicity and Proton Transfer in Protic Ionic Liquids”, Phys. Chem. Chem. Phys., 2010, 12, 10341-10347
3. G. Mullen and E. J. Maginn, “Reaction Ensemble Monte Carlo Simulations of Xylene Isomerization Under Confinement”, J. Chem. Theory Comput., 2017, 13, 4054-4062.