Infinite dilution activity coefficients from ab initio solvation calculations

A Group contribution solvation (GCS) model was developed to calculate infin ite dilution activity coefficients (gamma(infinity)) based on modern comput ational chemistry. The GCS model results in an average error of 7% in gamma (infinity) for the limited number of data points among water, n-hexane, ace tonitrile and n-octanol, whereas the errors are 47% and 52% with the UNIFAC model and the modified UNIFAC model, respectively. GCS was also used to ca lculate infinite dilution partition coefficients, which can be used to dete rmine how a dilute solute partitions between two solvents. Solutes were exa mined in three different liquid-liquid systems: water/n-hexane, water/aceto nitrile,and water/n-octanol. With GCS, the average errors are 22% (for 18 s olutes), 18% (for 14 solutes) and 14% (for 15 solutes) for these solvent sy stems, while comparable errors are 237%, 286% and 226% with UNIFAC; and 342 %, 414% and 306% with modified UNIFAC. The GCS model is a powerful new tool to predict the octanol-water partition coefficients.