Are Fluorination and Chlorination of the Morpholinium-Based Ionic Liquids Favorable?

TL;DR

This study uses high-accuracy computational methods to analyze the thermodynamics of fluorination and chlorination on morpholinium-based ionic liquids, revealing fluorination's higher energetic favorability and guiding future synthetic efforts.

Contribution

It provides the first thermodynamic analysis of halogenation on morpholinium-based cations using coupled-cluster calculations, highlighting differences between fluorination and chlorination.

Findings

Fluorination is more energetically favorable than chlorination.

Halogenation preferences vary by location and halogen type.

Electron density distribution correlates with halogenation favorability.

Abstract

Room-temperature ionic liquids (RTILs) constitute a fine-tunable class of compounds. Morpholinium-based cations are new to the field. They are promising candidates for electrochemistry, micellization and catalytic applications. We investigate halogenation (fluorination and chlorination) of the N-ethyl-N-methylmorpholinium cation from thermodynamics perspective. We find that substitutional fluorination is much more energetically favorable than substitutional chlorination, although the latter is also a permitted process. Although all halogenation at different locations are possible, they are not equally favorable. Furthermore, the trends are not identical in the case of fluorination and chlorination. We link the thermodynamic observables to electron density distribution within the investigated cation. The reported insights are based on the coupled-cluster technique, which is a highly accurate and reliable electron-correlation method. Novel derivatives of the morpholinium-based RTILs are discussed, motivating further efforts in synthetic chemistry.