Theoretical study on hydrophilicity and thermodynamic properties of polyfluorinated dibenzofurans

Logarithm values of octanol–water partition coefficients (log Kow) of polyfluorinated dibenzofurans (PFDFs) were calculated based on group contributions, and their thermodynamic properties in the ideal gas state at 298.15 K and 1.013 × 105 Pa were calculated using a combination of quantum mechanical computations performed with the Gaussian 03 program at the B3LYP/6-311G* level. The isodesmic reactions were designed to calculate standard enthalpy of formation (ΔHfθ) and standard free energy of formation (ΔGfθ) of PFDF congeners. By establishing relationships between these properties (including log Kow, standard state entropy Sθ, ΔHfθ,ΔGfθ) and the number and position of fluorine atom substituents (NPFS), it was found that the fluorine substitution pattern strongly influences all of these properties of the compounds. The relation curve of log Kow values varying with the fluorine substitution pattern presented a three-level sawtooth shape. Intramolecular repulsive forces exist between an oxygen-adjacent fluorine atom on phenyl ring and the oxygen of dibenzofuran, between ortho  -substituted fluorine atoms on a phenyl ring, and between two adjacent fluorine atoms on different phenyl rings. Their repulsion energies were ascertained by comparing ΔGfθ values to be approximately 14 kJ mol−1–17 kJ mol−1, 18 kJ mol−1–22 kJ mol−1 and 7 kJ mol−1–9 kJ mol−1, respectively. According to the relative magnitude of their ΔGfθ, the relative stability order of PFDF congeners was theoretically proposed.

► We obtained a complete database of log Kow and thermodynamic properties of PFDFs.
► Good relations exist between the properties and the substitution pattern.
► Three-level sawtooth shape of log Kow with the substitution pattern is presented.
► We compared PFDFs and their chlorinated, brominated analogs on the correlations.
► The relative stability order of PFDFs was theoretically proposed.