COSMO-RS Estimation of Henry s Law Constants and K OA for simple PAHs and O-, N- and S-substituted derivatives, and their temperature dependence.

Transcription

1 COSMO-RS Estimation of Henry s Law Constants and K OA for simple PAHs and O-, N- and S-substituted derivatives, and their temperature dependence. J. Mark Parnis, Donald Mackay and Tom Harner Trent University and Environment Canada, Ontario, Canada March 2015

2 Polycyclic Aromatic Hydrocarbons are persistent pollutants. Background Naphthalene Anthracene Partitioning to air from water or soil is only partly characterized, with limited T-dependence data. Phenanthrene Pyrene Data on O-, N- and S- substituted derivatives even more scarce. 1-amino-9,10-anthracenedione2

3 Polarity and Derivitization Anticipate significant differences in behavior due to relatively highly polar nature of derivatives. Positive polarization Negative polarization Benz[a]anthracene Benz[a]anthracene-7,12-dione 3

4 Molecular Partitioning Equilibrium partitioning of solute described by: Medium A air 3 1 ppah ( Pa) H ( Pa m mol ) water [ PAH ] Solute or contaminant K OA [ PAH ] [ PAH ] octanol air Medium B 4

5 Room-temperature Henry s Law Constant Comparison (Ma et al. data) Ma, Y.-G., Lei, Y. D., Xiao, H., Wania, F., Wang, W.- H J. Chem. Eng. Data, 55, 819. Agreement is excellent, RMSE =

6 Temperature-variable Henry s Law Comparison (Bamford et al. data) Agreement is also excellent. RMSE = Bamford, H.A., Poster, D.L., Baker, J.E., Environmental Toxicology and Chemistry, 18,

7 Enthalpy of vaporization estimates Very good correlation. One major outlier (chrysene) DH vap 45 kj mol -1 supported ln( H / Pa m 3 mol 1 ) DH RT DS R 7

8 Room-temperature Henry s Law Comparison for O-, N_ and S-substituted PAHs (Meyer dataset) Mixture of experimental and QSAR-based data Agreement is very good, with some spread. RMSE = 0.76 (all, red and blue) RMSE= 0.3 (experimental data only, red) Meyer, D., Dressler, H., Ruck, W., 2007 LC-GC North America, 25,

9 K OA prediction at room temperature (Ma et al. (x) and Odabasi et al. (o) datasets) Excellent correlation. Large systematic error present. Ma, Y.-G., Lei, Y. D., Xiao, H., Wania, F., Wang, W.-H J. Chem. Eng. Data, 55, 819. Odabasi, M., Cetin, E., Sofuoglub, A., 2006 Atmospheric Environment, 40,

10 K OA prediction quality with T variation Correlation with Harner/Bidleman is excellent. RMS error is very large (~1.65), indicating a large systematic error. Harner, T., Bidleman, T.F., 1998 J. Chem. Eng. Data, 43,

11 Is the output of COSMOtherm is selfconsistent? Test criterion: K AW xa x / x x / x K x x / x x / x K A O O W OW W W O O A OA log K log K log K AW OW OA 1-hexanol computed values at K (dry octanol) confirm this relation: mole fraction logkaw logkoa logkow logkow-logkoa data: value

12 Check after conversion to concentration: All looks good! mole fraction logkaw logkoa logkow logkow-logkoa data: value conc conversion add: conc data logkaw logkoa logkow logkow-logkoa value

13 Calc. vs experiment after conversion Correlation checks for a series of small molecules. Good experimental data is available on EPIsuite. Correlations good for all predictions 13

14 A last check for consistency K OA calculated from K OW and K AW (H) gives much better agreement! EPIsuite doesn t give references for this data! Must be a problem with the experiments! 14

15 Trends in estimated H with T Increases with T, as expected due to increased volatility. Increases of 1-2 log H units over -5 to 40 o C Trend present over 7 log H unit range. 15

16 Trends in estimated K OA with T Decreases with T, as expected due to increased volatility. Decreases of log H unit over -5 to 40 o C Trend present over 6 log K OA unit range. 16

17 Additive Trends for QSARs Functional Average Average Number of data group type D log H D log K OA averaged Methyl Dimethyl Ethyl Trimethyl Nitro Dinitro Keto Quinone Thio

18 The Fundamental Triangle of Partitioning We can use the partition coefficients for molecules to say something about their properties: Air K OA K K OW AW Methane K AW K OA Water Methanol Octanol Tissue K OW 18

19 What happens when we fluorinate? Air Hexafluoroacetone Tetrafluoromethane Methane Hexafluorobenzene ,5 0 0,5 1 1,5 2 2,5 3 3,5-1 Benzene -2 Methanol -3 Acetone Trifluoromethanol Water -4 Tissue -5 19

20 log Kaw What happens when we nitrate? 3 2 Methane Air Propane Water nitro methane Naphthalene nitro propane Fluorene Anthracene Pyrene 1-nitro naphthalene 1,3-dinitro naphthalene 2-nitro pyrene 2-nitro fluorene 2-nitro anthracene log Kow Tissue 20

21 Chemical Space Plot of T-dependence in H as K AW 21

22 Contact Information Prof. J. Mark Parnis Prof. Don Mackay Department of Chemistry and Centre for Environmental Modelling and Chemistry Trent University Peterborough ON Canada K9J 7B8 (705)