Can COSMOTherm Predict a Salting in Effect?

Area of Science:

• Physical Chemistry
• Atmospheric Chemistry
• Computational Chemistry

Background:

• Accurate prediction of solute solubility in electrolyte solutions is crucial for understanding atmospheric processes.
• The Setschenow equation and Setschenow constants (K_S) quantify the effect of salts on solute solubility.
• Computational methods are increasingly used to predict these interactions.

Purpose of the Study:

• To compute Setschenow constants (K_S) for various organic solute-salt combinations using the COSMO-RS method.
• To evaluate the performance of the COSMO-RS (COSMOTherm) model in predicting salting in and salting out effects.
• To assess the model's applicability to atmospherically relevant systems.

Main Methods:

• Utilized COSMO-RS, a hybrid quantum chemistry and statistical thermodynamics approach.
• Calculated Setschenow constants (K_S) for a wide range of organic solutes and inorganic salts.
• Compared computational predictions with available experimental data.

Main Results:

• COSMO-RS generally overpredicted salting out (positive K_S) and underpredicted salting in (negative K_S) compared to experimental values.
• Salt type significantly influenced predicted K_S values, with oxalates and sulfates showing larger effects than chlorides and bromides.
• The model failed to accurately predict salting in for glyoxal in sulfate solutions, highlighting limitations in atmospheric chemistry applications.

Conclusions:

• The COSMO-RS model, as implemented in COSMOTherm, shows systematic deviations from experimental Setschenow constants.
• While qualitatively predicting some salting in for alkylaminium salts, the model's quantitative accuracy is limited.
• Further refinement of the COSMO-RS model is needed for reliable predictions in atmospheric chemistry contexts.