Studies on Amino Acid Type Protic Ionic Liquid Comprising N-2-Ethylhexylethylenediaminium Cation Coupled with the dl-Hexanoylalaninate Anion

Abstract

An acyl-amino acid type protic ionic liquid (PIL) composed of N-2-ethylhexylethylenediaminium ([HEtHex-en]+) coupled with dl-hexanoylalaninate ([Hexala]−), forming dl-[HEtHex][Hexala], was newly synthesized. This PIL has chelate moieties on both the cationic and anionic sides. It is a room-temperature ionic liquid with a glass transition temperature of 237.55 K (−\u200935.6 °C) and is highly miscible with water (H2O, 90 wt.%) owing to its high polarity. The dynamic viscosity approximately follows the Arrhenius equation while the electrical conductivity slightly deviates from it in the temperature range 303.15–353.15 K. The Walden line of dl-[HEtHex][Hexala] in the same temperature range is found to be outside the ΔW\u2009=\u20091 region. dl-[HEtHex][Hexala] enables the encapsulation of transition metal ions, and the measurements with inductive coupled plasma emission have shown that the solubilities of CuCl2, CoCl2 and NiCl2 in dl-[HEtHex][Hexala] are 74.5, 65.2, and 17.6 mmol·kg−1, respectively.