Hydrogen bond donor and alcohol chain length effect on the physicochemical properties of choline chloride based deep eutectic solvents mixed with alcohols

Abstract

Deep eutectic solvents are mixtures typically composed by a hydrogen bond donor and a hydrogen bond acceptor. They have appeared as an alternative of ionic liquids in several processes due to their tunability, biodegradability and low cost. Recently, deep eutectic solvents have been studied as potential solvents for different applications. Then, their physicochemical properties need to be characterized for understanding the interaction between its constituents and with other compounds. Deep eutectic solvents prepared for this work are based on choline chloride mixed with ethylene glycol, 1,3-propanediol or 1,4-butanediol at a 1:3 mol ratio. FT-IR spectra was obtained for comparing the different structures of those deep eutectic solvents. Density and viscosity of the prepared deep eutectic solvents were measured from 293.15 K to 333.15 K at 101.13 kPa. Also, the same properties at the same temperature and pressure conditions were obtained for the mixtures of the three deep eutectic solvents with four alcohols: methanol, ethanol, 1-propanol or 1-butanol. Physicochemical (i.e density and excess volume) and transport properties (i.e viscosity) were measured and predicted using PC-SAFT and Free Volume Theory, respectively, for understanding the effect of the temperature variation, the length of the alcohol chain, and length of the hydrogen bond donor on the configurational aspects of the mixture. Subsequently, a prediction of the excess molar enthalpy was performed with COSMO-RS in order to assess the behavior of the same variables on different type of intermolecular interactions from the energetic point of view. The results suggest that mixing each deep eutectic solvent with an alcohol produce negative molar excess volumes and molar excess enthalpies, observing a higher affinity between unlike species.