Computing Kinetic Solvent Effects and Liquid Phase Rate Constants Using Quantum Chemistry and COSMO-RS Methods.

Area of Science:

• Computational chemistry
• Chemical kinetics
• Physical chemistry

Background:

• Industrially and environmentally relevant reactions occur in the liquid phase.
• Accurate prediction of liquid phase rate constants is essential for analyzing kinetic mechanisms.
• Current computational methods (quantum chemistry, continuum solvation) have unknown errors and lack standardized workflows.

Purpose of the Study:

• To assess the accuracy of various quantum chemical and COSMO-RS (COnductor-like Screening Model - Realistic Solvation) levels of theory for predicting liquid phase rate constants and kinetic solvent effects.
• To establish a consistent computational workflow for these predictions.
• To evaluate the computational errors associated with different theoretical approaches.

Main Methods:

• Gas phase rate constants were computed first.
• Solvation corrections were applied using various quantum chemical and COSMO-RS methods.
• The accuracy of predictions was evaluated against experimental data for 191 rate constants across 15 reactions and 49 solvents.
• Relative rate constants were analyzed to isolate solvation calculation errors.

Main Results:

• The combination of ωB97XD/def2-TZVP (quantum chemistry) and COSMO-RS at the BP-TZVP level demonstrated the best performance for liquid phase rate constants, yielding a mean absolute error of 0.90 in log10(k_liq).
• Predictions of relative rate constants showed high accuracy across most tested methods, with a mean absolute error of 0.27 in log10(k_solvent1/k_solvent2).

Conclusions:

• The study identified optimal computational parameters for predicting liquid phase reaction rates.
• The findings provide a more reliable computational workflow for chemical kinetics in solution.
• Accurate prediction of kinetic solvent effects is achievable with current computational tools.