Assessing the Temperature-Dependent Tunable Polarity of N,N-Dimethylcyclohexylamine (DMCHA) and Water Mixtures

The promise of switchable solvents as green solvent alternatives lies in the ability to drastically alter their properties based on an external trigger. Switchable hydrophilicity solvent N,N-dimethylcyclohexylamine, DMCHA, is known to change properties based on both CO2 addition and variations in temperature, both in the presence of water. While the impact of temperature has been observed via changes in water solubility, the solvent properties underlying these observations have not been quantified. Kamlet-Taft solvatochromic parameters (alpha, beta, and pi*) and dielectric constants for DMCHA and DMCHA-water mixtures were measured across a temperature range of 25-60 degrees C. Temperature swing effects of DMCHA in addition to CO2-switching capabilities were validated and quantified on the Kamlet-Taft polarity scale. Notably, binary mixtures of water in DMCHA show promising tunability in terms of its beta and pi* parameters induced by moderate variations in temperature. Potential applications for this CO2-switchable and temperature-tunable solvent are discussed.