Low viscosity lactam-based ionic liquids with carboxylate anions: Synthesis, characterization, thermophysical properties and mutual miscibility of ionic liquid with alcohol, water, and hydrocarbons

Abstract

Low viscosity lactam-based ionic liquids (ILs) were synthesized by a neutralization reaction between a cyclic amide (lactam), such as γ-butyrolactam, ε-caprolactam, 12-aminododecanolactam, and 1-octyl-2-pyrrolidone with a Brønsted acid (acetic, butyric, or hexanoic acids), in a total of eight systems. From this experimental matrix, the following five ILs have been formed: γ-butyrolactam + acetic acid (BTA), γ-butyrolactam + butyric acid (BTB), and γ-butyrolactam + hexanoic acid (BTH); and, ε-caprolactam + acetic acid (CPA) and ε-caprolactam + hexanoic acid (CPH), all systems presenting low viscosity. All synthesized ILs were characterized by FTIR and 1H NMR spectroscopies. Volumetric and transport properties (density and viscosity), along with thermal decomposition and ionic conductivity analyses have been experimentally determined. Mutual miscibility of these ILs against n-butanol, water, toluene, heptane, ethylbenzene, styrene, cyclohexane, and cyclohexene systems were determined at 293.15 K and atmospheric pressure (P = 101.325 kPa). Cation and anion structures influence on the mixtures were discussed. Ionic liquids containing lower chain anions formed two phases with heptane and were completely miscible in aromatic hydrocarbons, water and n-butanol. While ionic liquids with higher chain anions showed partial miscibility only in water. The miscibility of n-heptane increases when the hydrophobic character of ILs increases, as observed for ILs produced from γ-butyrolactam (BTA, BTB, and BTH). ILs-solvents miscibilities are a function of the lactam ring chain, decreasing in aliphatic hydrocarbons and increasing in cyclic hydrocarbons.