Effect of Substituent Groups in Anions on Some Physicochemical Properties of 1‑Butyl-3-methylimidazolium Carboxylate Ionic Liquids

Abstract

In this work, four 1-butyl-3-methylimidazolium carboxylate ionic liquids (ILs) with different substituent groups in anions, including 1-butyl-3-methylimidazolium glycollate [C₄mim]­[HOCH₂COO], 1-butyl-3-methylimidazolium lactate [C₄mim]­[CH₃CHOHCOO], 1-butyl-3-methylimidazolium benzoate [C₄mim]­[C₆H₅COO], and 1-butyl-3-methylimidazolium glycinate [C₄mim]­[H₂NCH₂COO], have been synthesized and characterized. Their densities (ρ) and surface tensions (γ) have been determined experimentally in the temperature range of (298.15 to 343.15) K. By using thermodynamic and empirical equations, molar volume (<i>V</i>_m), isobaric expansivity (α_<i>p</i>), standard entropy (<i>S</i>°), lattice energy (<i>U</i>_POT), surface excess entropy (<i>S</i>_s), vaporization enthalpy (Δ_l^g<i>H</i>_m⁰) and Hildebrand solubility parameter (δ_H) of these ILs have been derived from density and surface tension data. The effects of substituent groups in carboxylate anions on densities and surface tensions of these ILs have been assessed from the analysis of the structure–property relationship