The Entropy of Deep Eutectic Solvent Formation

The standard entropies S(298°E) of deep eutectic solvents (DESs), which are liquid binary mixtures of a hydrogen bond acceptor component and a hydrogen bod donor one, are calculated from their molecular volumes, derived from their densities or crystal structures. These values are compared with those of the components—pro-rated according to the DES composition—to obtain the standard entropies of DES formation Δ(f)S. These quantities are positive, due to the increased number and kinds of hydrogen bonds present in the DESs relative to those in the components. The Δ(f)S values are also compared with the freezing point depressions of the DESs Δ(fus)T/K, but no general conclusions on their mutual relationship could be drawn.