Methylation Effects on the Melting Points of Thiazolium Ionic Liquids — 17a — Brodey Ballinger, Jace Cofer

Ionic liquids (ILs) are a class of versatile organic salts with melting points below 100 °C which have garnered attention for their potential applications, including use as green solvents, electrolytes, and antimicrobials. In imidazolium ILs, it has been shown that a single methylation of the imidazolium ring can increase the melting point by over 100 °C. Previously, it has been theorized that this methylation reduces the cation’s conformational flexibility through steric hindrance, thereby decreasing entropy and raising the melting point. Conversely, it has also been hypothesized that the large melting point increase upon methylation is primarily determined by disruption of the hydrogen bonding between cation’s ring hydrogens with the anion. Here, the impact of methylation on the melting point of thiazolium-based ILs is reported. Twelve thiazolium ILs were synthesized and characterized by their melting points and through molecular dynamics simulations. The data support the hypothesis that the presence and position of the cation’s methyl groups notably influence the melting points of ILs through steric hindrance effects which reduce alkyl group flexibility. These results help provide deeper insight into how structural variations in the organic cation help determine the physical properties of ILs. Such structure-property relationships are crucial to understand for the rational synthesis of ILs with desirable characteristics for specific applications.

Dakota Wesleyan University
Dr. Adam Sturlaugson