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The density, surface tension, and viscosity of ionic liquids (1-ethyl-3-methylimidazolium diethylphosphate and 1,3-dimethylimidazolium dimethylphosphate) and ternary mixtures with aqueous MDEA, were measured over the whole concentrations range at various temperatures (293.15–343.15) K by using Anton Paar DMA 4500 densimeter, Kruss Processor Tensiometer K100, and R/S+ Brookfield rheometer. The experimental density and surface tension decrease linearly with mole fractions of ionic liquids. Data on viscosity demonstrates a temperature-dependence behavior, that decreased nonlinearly with temperature. Evaluations of the measured physicochemical properties were completed. The best correlation for density and surface tension data were linear fitting, while the viscosity data was obtained by polynomial regression. ILs mole fraction also influenced the experimental density, surface tension, and viscosity. The Jouyban–Acree model was used to correlate the physicochemical properties of the mixtures and pure compounds at different temperatures. The absolute percentage error (APER) for each correlations was less than 8 %, proving that this model accurately represents the physicochemical properties data.

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The antiradical efficiency (AE) and kinetic behavior of a new ferulate-based protic ionic liquids (PILs) were described using 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical assay. The reduction of the DPPH free radical (DPPH•) was investigated by measuring the decrease in absorbance at 517 nm. The time to reach steady state for the reaction of parent acid (ferulic acid) and synthesized PILs with DPPH• was continuously recorded for 1 h. Results revealed that the AE of 2-butylaminoethanol ferulate (2BAEF), 3-dimethylaminopropanol ferulate (3DMAPF) and 3-diethylaminopropanol ferulate (3DEAPF) PILs have improved compared to ferulic acid (FA) as the reaction class changes from low to medium. This attributed to the strong hydrogen abstraction occurred in the PILs. Furthermore, these PILs were found to have a good kinetic behavior compared to FA due to the high rate constant (k2) (164.17, 242.84 and 244.73 M−1 s−1, respectively). The alkyl chain length and more alkyl substituents on the nitrogen atom of cation were believed to reduce the cation-anion interaction and speed up the hydrogen atom transfer (HAT) and electron transfer (ET) mechanisms; hence, increased rate constant was observed leading to a strong antioxidant activity of the synthesized PILs.

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