Characterizing N,N-Dimethylcyclohexylamine (DMCHA) across Temperature Using Kamlet?Taft ?, ?, and ?* Parameters

Switchable Hydrophilicity Solvents (SHSs) are potential green solvent alternatives for the extraction of high-value products. The use of SHS may reduce process energy costs associated with solvent separations and the number of required extraction steps.1 One promising SHS, N,N-dimethylcyclohexylamine (DMCHA) has been shown to radically change its hydrophilicity with the use of CO2 as a trigger in the presence of water.2 In addition to this drastic change from hydrophobic to hydrophilic, tuning of DMCHA’s hydrophobicity can be achieved by small changes in temperature and can further enhance the applicability of this solvent.3 The objective of this study is to determine the Kamlet-Taft solvent solubility parameters (𝞪, 𝜷, 𝝅*) for DMCHA across a range of temperatures with various dissolved water concentrations to more fully understand the range of DMCHA’s solvation capacity. The solvatochromic effect was measured via four commonly used solvatochromic probes (4-Nitroanisole, 4-Nitroaniline, N,N-dimethyl-4-nitroaniline, and Reichardt’s dye) in a UV-Vis Spectrophotometer. The 𝞪, 𝜷, and 𝝅* parameters were determined for 1, 3, and 5wt% water in DMCHA solutions along with Switched DMCHA (SDMCHA) and three reference solvents (water, DMSO, and Cyclohexane) at temperatures ranging from 25°C to 60℃. It was found that the polarizability (𝝅*) of DMCHA a strong function of water content and temperature - increases in water content and decreases in temperature lead to lower values of 𝝅*. Furthermore, the relationship between temperature and water content is complex where larger water contents lead to a larger decrease in 𝝅* across temperature. These findings illustrate the potential versatility and tunability of DMCHA as an alternative to conventional solvent based extraction methods.