Quantitative prediction of K values

Introduction

Fragment models
sp-LFERs
pp-LFERs
Comparison of the various methods
Predictive models based on molecular structure

Critical remarks on approaches from chemical engineering

Selftest
Problems
     Problem 1
     Problem 2
     Problem 3
           Answer
     Problem 4
           Answer
     Problem 5
           Answer
     Problem 6
           Answer
     Problem 7
     Problem 8
     Problem 9

Problem 3

a) Calculate the Koc/water values of phenol and benzene with the software KOCWINTM supplied by U.S. EPA. Compare and discuss the results.

Answer:
Phenol is a highly bipolar compound while benzene is not. This should typically result in very different partition behaviour unless the two phases in the partition system are almost identical in their polarity. The latter is certainly not the case with water and soil organic matter, hence, different Koc values should be expected.


b) Calculate the Koc/water value of 1,2-ethanediol with KOCWINTM and discuss the result.

Answer:
In all cases where KOCWINTM does calculate a negative log Koc value (i.e. a Koc value smaller than 1) this value is deliberately corrected to 0 by the software (i.e. Koc = 1). It is not clear why this is done but it is definitely clear that negative log Koc values are realistic for highly polar organic compounds (i.e., these compounds prefer the water phase over the soil organic carbon phase) so that this correction is not justified.

 

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