Effect of Aromaticity in Anion on the Cation-Anion Interactions and Ionic Mobility in Fluorine-Free Ionic Liquids.

ABSTRACT: Ionic liquids (ILs) composed of tetra(n-butyl)phosphonium [P₄₄₄₄]⁺ and tetra(n-butyl)ammonium [N₄₄₄₄]⁺ cations paired with 2-furoate [FuA]^-, tetrahydo-2-furoate [HFuA]^-, and thiophene-2-carboxylate [TpA]^- anions are prepared to investigate the effects of electron delocalization in anion and the mutual interactions between cations and anions on their physical and electrochemical properties. The [P₄₄₄₄]⁺ cations-based ILs are found to be liquids, while the [N₄₄₄₄]⁺ cations-based ILs are semi-solids at room temperature. Thermogravimetric analysis revealed higher decomposition temperatures and differential scanning calorimetry analysis showed lower glass transition temperatures for phosphonium-based ILs than the ammonium-based counterparts. The ILs are arranged in the decreasing order of their ionic conductivities as [P₄₄₄₄][HFuA] (0.069 mS cm^-1) > [P₄₄₄₄][FuA] (0.032 mS cm^-1) > [P₄₄₄₄][TpA] (0.028 mS cm^-1) at 20 °C. The oxidative limit of the ILs followed the sequence of [FuA]^-> [TpA]^-> [HFuA]^-, as measured by linear sweep voltammetry. This order can be attributed to the electrons' delocalization in [FuA]^- and in [TpA]^- aromatic anions, which has enhanced the oxidative limit potentials and the overall electrochemical stabilities.

SUBMITTER: Khan IA 

PROVIDER: S-EPMC7872428 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature