Prediction of the air-water partition coefficient for perfluoro-2-methyl-3-pentanone using high-level Gaussian-4 composite theoretical methods

Abstract

The air-water partition coefficient (K_aw) of perfluoro-2-methyl-3-pentanone (PFMP) was estimated using the G4MP2/G4 levels of theory and the SMD solvation model. A suite of 31 fluorinated compounds was employed to calibrate the theoretical method. Excellent agreement between experimental and directly calculated K_aw values was obtained for the calibration compounds. The PCM solvation model was found to yield unsatisfactory K_aw estimates for fluorinated compounds at both levels of theory. The HENRYWIN K_aw estimation program also exhibited poor K_aw prediction performance on the training set. Based on the resulting regression equation for the calibration compounds, the G4MP2-SMD method constrained the estimated K_aw of PFMP to the range 5–8 × 10⁻⁶ M atm⁻¹. The magnitude of this K_aw range indicates almost all PFMP released into the atmosphere or near the land-atmosphere interface will reside in the gas phase, with only minor quantities dissolved in the aqueous phase as the parent compound and/or its hydrate/hydrate conjugate base. Following discharge into aqueous systems not at equilibrium with the atmosphere, significant quantities of PFMP will be present as the dissolved parent compound and/or its hydrate/hydrate conjugate base.

Keywords:

• Perfluoro-2-methyl-3-pentanone
• perfluorinated compounds
• air-water partitioning
• theoretical study
• quantum chemistry composite methods

Funding

This work was supported by a SIAST Seed Applied Research Program grant to K. Forest, and was made possible by the facilities of the Western Canada Research Grid (WestGrid: Project 100185), the Shared Hierarchical Academic Research Computing Network (SHARCNET: Project sn4612), and Compute/Calcul Canada.