New Binary Mixture Ionic Liquid Based On Quaternary Ammonium Salt/Caprolactam

In recent years, ionic liquids are attracting increased attention worldwide because they have been shown to function as novel green reaction media. As far as we know, an ionic liquid typically consists of organic nitrogen-containing heterocylic cations and inorganic anions. Here, a novel room-temperature binary mixture ionic liquid based on quaternary ammonium salt and caprolactam has been synthesized and characterized by pH, liquid-solid phase diagram, solubility, conductivity and cyclic voltammetry. This molten salt appears as a liquid at <100°C, though it is composed of two solids. The melting points of the binary ionic liquid vary with the different content of caprolactam. For example, the C6H11NO/(C4H9)4NHSO4 binary mixture ionic liquid, according to the analysis of its liquid-solid phase diagram, the eutectic point is about 28°C with the mass percentage of caprolactam 75%. This work has shown that mixtures of caprolactam with quaternary ammonium salts form low melting point binary mixture ionic liquid that have unusual solvent properties.

Key words: binary mixture, phase diagram, caprolactam