Novel diglycolic acid-based deep eutectic solvents and their applications as a rust remover

Two novel environmentally friendly deep eutectic solvents (DESs) were synthesized for the first time from diglycolic acid (DGA) as a hydrogen bond donor (HBD) in a combination with choline chloride (ChCl) and tetrabutylammonium hydrogen sulfate (TBAHS) as hydrogen bond acceptors (HBAs) at a molar ratio of (1:1). The physicochemical properties of the synthesized DESs including density (1.11057–1.263569 g·cm−3), speed of sound (1560.15–2105.22 m·s−1), electrical conductivity (1.982–773.6 μS·cm−1), viscosity (500–38,275 mPa·s), refractive index (1.458699–1.48690), and surface tension data (42.82–67.688 mN·m−1) were measured as a function of temperature. Temperature dependencies of all the measured properties were successfully correlated by a general exponential equation. Furthermore, in order to confirm the chemical structure and purities of the synthesized DESs as well as occurrence of hydrogen bond interactions between the HBAs and HBD components, the FT-IR, 1H, and 13C NMR analysis of the DESs were also carried out. These new DESs were applied as rust removal agents due to their super acidity properties (pHDES1 = −3.63 and pHDES2 = −2.08) and exhibited excellent potentials for removing rust at different temperatures. The ChCl-DGA DES showed an interesting ability for removal rusts at 120 °C in very short time removal process, but the TBAHS-DGADES does not show such ability. © 2020