() Prediction of Henry's law constant of organic compounds in water at 25°C by a fragment method.
Schüürmann, G.1, Ebert, R.-U.1, Kühne, R.1, 1 UFZ Centre for Environmental Research, Leipzig, Germany
ABSTRACT- Henry's law constant is one of the most important compound properties in environmental modelling. Even though lots of measurements for organic compounds have been published in the last decade, there are still significantly less data available than for other important properties as water solubility or vapour pressure. A new fragment method is presented to predict Henry's law constant of organic compounds in water at 25°C in terms of the - dimensionless - partition coefficient air/water. A training set of about 2000 compounds covering all important compound classes was compiled to develop this model. Validated experimental data were taken from direct measurements as well as from consistent vapour pressure / water solubility pairs. The new technique consists of about 180 descriptors. While there are ca. 35 basis fragments in terms of common atom types and functional groups, the majority of the parameters are more complex correction factors to account for particular structural characteristics. The prediction power of the new model, together with its superiority to existing methods, is demonstrated by an external prediction set of about 200 compounds not included in the model development. Opportunities to further improve the reliability of the predictions are discussed.
Key words: partition coefficient air/water, Henry's law constant, estimation method, fragment method