Solvent-free synthesis of protic ionic liquids. Synthesis, characterization and computational studies of triazolium based ionic liquids

• Published in: Journal of molecular liquids Vol. 360; p. 119358
• Main Authors: Morais, Eduardo Maurina, Abdurrokhman, Iqbaal, Martinelli, Anna
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.08.2022
• Subjects: Acidity; DFT; Protic Ionic Liquid; Solvent-free; Synthesis; Vibrational Assignment; Vibrational Assignment; Acidity; Synthesis; DFT; Protic Ionic Liquid; Solvent-free
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2022.119358

[Display omitted] •Solvent-free synthesis method that yields high purity and dry protic ionic liquids.•The synthesis method is described in detail, including a video tutorial.•The imidazolium compounds showed higher thermal stability when compared to the triazolium ones.•DFT was used hypothesize on the increased acidity of triazolium protic ionic liquids. A series of triazolium and imidazolium based protic ionic liquids were synthesized using a solvent-free method designed to address several limitations encountered with other commonly used methods. Using this method, pure (98–99% m/m) and dry (128–553 ppm of water) protic ionic liquids were synthesized (in a laboratory scale) without the need for purification methods that require heating the ionic liquid, hence avoiding the common issue of thermal decomposition. This method was also designed to allow for the accurate measurement of acid and base, and for the controlled mixing of both compounds, which is essential to avoid producing impure protic ionic liquids with excess of either acid or base. The system is constructed of only glass and chemically resistant polymer (PTFE and PVDF) parts, which avoid other contaminants that can result from unwanted reactions involving the reagents with common laboratory tools (metallic objects, paper, plastic, etc.). This process is described in detail in the paper as well as in a video. The resulting ionic liquids were carefully analyzed by spectroscopic and thermal methods designed to avoid water absorption, which is known to affect their properties. To complement this experimental characterization, computational chemistry tools were used to assess the ionic liquids’ properties, as well as to assign vibrational modes.