Phenol-cyclohexanol eutectic mixtures: Phase diagram and microscopic structure by experimental and computational studies

Abstract

• Non ionic eutectic solvents: phenol-cyclohexanol mixture. • SLE phase diagram by DSC experiment. • Microscopic structure and hydrogen bonding by IR spectroscopy, X-ray diffraction and theoretical calculations. Non ionic deep eutectic solvents (type V) have been recently proposed as innovative and alternative solvents. Prepared by mixing the starting components, their mixtures show strong deviations from thermodynamic ideality. An example of deep eutectic solvent is the 1:1 thymol-menthol mixture: deviations from ideality are originated from the strength of the hydrogen bond between different components. With the aim to investigate the role of hydrogen bonding in the non-ideality of mixtures of phenolic and alcoholic compounds, we studied the phase diagram and the structural properties of cyclohexanol and phenol mixtures coupling experimental and computational techniques. The phase diagram was measured by differential scanning calorimetry (DSC) providing a lowest melting point at about -35°C . The microscopic structure of eutectic composition was characterized by infrared spectroscopy (FT-IR), DFT and classical molecular dynamic simulations. The X-ray pattern was compared with MD results with the aim to describe the intermolecular interactions between phenol and cyclohexanol. The deviations from ideal mixing seem to be smaller than those observed for the 1:1 thymol-menthol mixture. The nature of intermolecular interactions in the phenol-cyclohexanol system has been compared with that of the thymol-menthol system by quantum chemistry calculations. In both the systems heteroassociation is energetically preferred to homoassociation because hydrogen bonding is stronger between different components, however van der Waals contributions involving alkyl groups can play an additional and significant role in the intermolecular association of the thymol-menthol system.