Measurement and Correlation of Densities, Refractive Indices, and Viscosities of Phosphonium Based Deep Eutectic Solvents at Several Temperatures Ranging from 293.15 to 323.15 K

An experimental study of densities, refractive indices and viscosities of nine deep eutectic solvents (DESs) at seven different temperatures ranging from 293.15 to 323.15 K at 5 K intervals is reported. One family of DESs is prepared by methyltriphenylphosphonium bromide (MTPPB) as a hydrogen bond acceptor (HBA) and ethylene glycol as a hydrogen bond donor (HBD). Another is prepared by allyltriphenylphosphonium bromide (ATPPB) as an HBA and ethylene glycol as an HBD to investigate the effect of the molecular structure of the HBA on the physical properties of DESs. While the values of density and viscosity of MTPPB based DESs are higher than those of ATPPB based DESs, refractive index values of MTPPB based DESs are lower than those of ATPPB based DESs. The impacts of temperature and mole ratio between HBA and HBD in DESs on physical properties were also assessed. Three equations were used to correlate viscosity data with respect to temperature, resulting in a good degree of correlation. In addition, Eyring's absolute rate theory was applied to deduce molar Gibbs-free energy of activation for DESs as a function of temperature.