Metrics for estimating vapour pressure deviation from ideality in binary mixtures.

A novel method is introduced for estimating the degree of interactions occurring between two different compounds in a binary mixture resulting in deviations from ideality as predicted by Raoult's law. Metrics of chemical similarity between binary mixture components were used as descriptors and correlated with the Root-Mean Square Error (RMSE) associated with Raoult's law calculations of total vapour pressure prediction, including Abraham descriptors, sigma moments, and several chemical properties. The best correlation was for a quantitative structure-activity relationship (QSAR) equation using differences in Abraham parameters as descriptors (r² = 0.7585), followed by a QSAR using differences in COSMO-RS sigma moment descriptors (r² = 0.7461), and third by a QSAR using differences in the chemical properties of log K_AW, melting point, and molecular weight as descriptors (r² = 0.6878). Of these chemical properties, Δlog K_AW had the strongest correlation with deviation from Raoult's law (RMSE) and this property alone resulted in an r² of 0.6630. These correlations are useful for assessing the expected deviation in Raoult's law estimations of vapour pressures, a key property for estimating inhalation exposure.