Deep eutectic solvents (DESs) are classified as a mixture of a quaternary ammonium salt and a hydrogen bond donor that melts below 100 °C. When mixed, the DES has lower lattice energy and therefore lower melting and freezing temperatures than the individual components. DESs are used today as media replacements for processes such as metal electrodeposition, metal electropolishing, battery cells, and synthesis applications. While many DESs are known in the literature, none have yet been reported that include a redox-active organic material as part of the solvent itself. We selected salicylic acid and gentisic acid as initial targets for redox-active hydrogen bond donors. The Antioxidant DESs, comprising salicylic acid:choline chloride (SC) and gentisic acid:choline chloride (GC), were mixed in molar ratios of 1:3, 1:2, 2:3, 1:1, 3:2, and 2:1 to find the ratio that exhibits the lowest melting point: the true eutectic mixture. SC mixtures were analyzed using a melting point apparatus, while some GC mixtures exhibited a liquid phase even at room temperature. These mixtures were also analyzed by cyclic voltammetry; both SC and GC were found to retain the well-known antioxidant electrochemistry observed for salicylic acid and gentisic acid in aqueous solutions, albeit with highly shifted redox potentials and kinetics. Further analyses of molecular composition and freezing points are in progress for both DESs. We believe these to be the most highly concentrated liquid antioxidant formulations, known concentrations of SC and GC are approximately 5 M.

Properties of antioxidant deep eutectic solvents

253rd National Meeting (2017)

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