Abstract
Equilibrium partition coefficients or partition ratios are a fundamental concept in physical chemistry, with wide applications in environmental chemistry. While comprehensive data compilations for the octanol–water partition ratio and the Henry’s law constant have existed for many years, no comparable effort for the octanol–air partition ratio (KOA) exists. Considering the increasing use of KOA in understanding a chemical’s partitioning between a wide variety of organic phases (organic phases in atmospheric particles, plant foliage, polymeric sorbents, soil organic matter, animal tissues, etc.) and the gas phase, we have compiled all KOA values reported in the published literature. The dataset includes more than 2500 experimentally derived values and more than 10 000 estimated values for KOA, in total covering over 1500 distinct molecules. The range of measured log10 KOA values extends from −2 to 13. Many more measured values have been reported in the log10 KOA range from 2 to 5 and from 6 to 11 compared to the range from 5 to 6, which is due to the complementary applicability range of static and dynamic measurement techniques. The compilation also identifies measured data that are judged not reliable. KOA values for substances capable of undergoing strong hydrogen bonding derived from regressions with retention times on nonpolar gas chromatographic columns deviate strongly from values estimated by prediction techniques that account for such intermolecular interactions and should be considered suspect. It is hoped that the database will serve as a source for locating existing KOA data and for the calibration and evaluation of new KOA prediction techniques.
Highlights
Understanding the affinity of a chemical for liquid octanol, liquid water, and the gas phase is often the first step to understanding its potential environmental and biological fate and behavior
keywords: Octanol–air partition coefficient (KOA) values for substances capable of undergoing strong hydrogen bonding derived from regressions with retention times on nonpolar gas chromatographic columns deviate strongly from values estimated by prediction techniques that account for such intermolecular interactions and should be considered suspect
The values included in the database were reported as KOA or log10 KOA values; 1409 values were derived from reported Ostwald coefficients in octanol (Loct), Henry’s law constants in octanol, the Gibbs energies of dissolution into octanol from the gas phase (∆G○, J mol−1), or activity coefficients of a chemical in octanol at infinite dilution (γ∞ o )
Summary
Understanding the affinity of a chemical for liquid octanol, liquid water, and the gas phase is often the first step to understanding its potential environmental and biological fate and behavior. While in the literature the thermodynamic property is more commonly referred to as a partition coefficient, we follow IUPAC nomenclature guidelines and describe the distribution of a chemical between two phases at equilibrium as a partition ratio. The unitless octanol–air partition ratio (KOA) describes the distribution of a chemical between octan-1-ol (CAS No 111-87-5) and the gas phase at equilibrium, KOA = CO/CA,. Many comprehensive reviews (Mackay et al, 2015) and databases of octanol–water partition ratios (KOW) (Leo et al, 1971), Henry’s law constants (kH) (Mackay and Shiu, 1981; Sander 2015), and other physical–chemical properties [e.g., Mackay et al (2006); Rumble et al (2019); US EPA (2012)] exist in the literature. The assembled database should be an easy-to-look-up repository of existing KOA data and be suitable for evaluating existing KOA prediction techniques and the development of new ones
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