Influence of the cation partner on levulinate ionic liquids properties

In the context of bio-based ionic liquids (ILs), in recent years levulinate ILs have been explored in various applications with appreciable performances. To expand their scope of use, seven selected levulinate ILs featuring different cationic moieties have been prepared and their physico-chemical properties compared. While all the ILs generated displayed only glass transitions at low temperature (<-60 degrees C), [C(4)C(1)Pyr]Lev presented melting and crystallization events. The thermal stability determined by TGA decreased in the order [P-8881]Lev > [C(2)C(1)Im]Lev approximate to [C(4)C(1)Im]Lev > [C(2)C(1)Pip]Lev > [C(2)C(1)Pyr]Lev approximate to [C(4)C(1)Pyr]Lev > [N-8881]Lev, and is in good agreement with the general trend observed for carboxylate ILs. In terms of viscosity, the LevILs showed a Newtonian behaviour when considering the shearing rates range, with a marked reduction of the viscosity at increasing temperatures. The glassy behaviour of LevILs was further ascertained applying the MYEGA viscosity-based model for the determination of the fragility index. The density of the LevILs was found to vary in the vicinity of 1 g/cm(3), and the systematic refractive index increase with increasing density was identified as a general trend. The refractive index was experimentally determined at five different wavelengths and several temperatures between 80 degrees C and 130 degrees C and followed the order [C(2)C(1)Im]Lev > [C(2)C(1)Pip]Lev > [C(4)C(1)Im]Lev > [C(2)C(1)Pyr]Lev > [C(4)C(1)Pyr]Lev > [P-8881]Lev > [N-8881]Lev. Overall, the possibility to tune the physico-chemical properties of ILs through structural variations of the cationic part has been proven valid for the LevIL family. When compared with the carboxylate ILs described in the literature, LevILs show great potential for further applicative studies. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

The article compares the physico-chemical properties of seven selected levulinate ILs, demonstrating the potential to tune the properties of ILs through structural variations of the cationic part. The study found that LevILs exhibit different thermal stability and density at different temperatures, which is of significant importance for further applicative studies.