Synthesis of tetramethylpiperidine 1-oxyl-based functional ionic liquids (FTILs), volumetric properties and thermodynamics of the activation for viscous flow of (FTILs + water) binary systems

Abstract

The application of tetramethylpiperidine 1‑oxyl (TEMPO)-based ionic liquids is a newly emerging area in the fields of the extraction natural compounds. Herein, TEMPO-based functional ionic liquids (FTILs) [CnTr][TEMPO-OSO3] (n = 2, 4, 6, 8, 10, 12, 14, 16) were synthesized and characterized by FT-IR, 1H NMR, 13C NMR and high-resolution mass spectrometry. The volumetric properties and thermodynamics of the activation for viscous flow of (FTILs + water) binary systems were measured. Under the experimental conditions, with the increase of hydrophobic side chain length, the interaction between FTILs and solvent decreases and the interaction between FTILs ions and FTILs ions increases. The FTILs are water-structure-making solutes. The activation process of the solutes for viscous flow of the binary systems is an isocoulomb reaction. A semi-empirical method is an effective method to predict the viscosity of the binary systems within a certain concentration range (m < 0.9 mol·kg−1).