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Physical & Chemical properties

Partition coefficient

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Description of key information

Key result for CAS # 756-13-8:
The log P for CAS# 756-13-8 is 5.48 ± 0.87 estimated by use of QSAR, ACDLabs v.12.00. The result is considered valid but of limited environmental significance because of a short (< 2.5 minutes) hydrolysis half-life.
Key result for PFPA (degradation product), CAS# 422-64-0:
pH-dependent octanol-water partition coefficient for PFPA:
at pH 5.5, -1.31
at pH 7, -1.33
at pH 8.5, -1.33
calculated using ACD/Labs v12.00

Key value for chemical safety assessment

at the temperature of:
20 °C

Additional information

Discussion for CAS# 756-13-8:

The partition coefficient, log P, was estimated by use of QSAR simulations for CAS# 756-13-8. The key study calculates a log P of the test substance in the aquatic compartment using proprietary software purchased from ACD/Labs v12.00. This QSAR is based on generally accepted simulation software the use of which has been published in peer-reviewed literature. The software's training set contains a number of fluorinated and perfluoronated chemicals, and in particular includes a closely related ethyl ester and therefore, the test substance is considered to be within the applicability domain of the model. This study is classified as acceptable as a QSAR simulation of log P, which is a relevant parameter for determination of transport and distribution of chemicals in the environment.

Discussion for PFPA (degradation product), CAS# 422-64-0:

The partition coefficient for PFPA to freshwater organisms was addressed by use of QSAR simulations. The key study calculates a pH-dependent log P (or log D) of the test substance in the aquatic compartment using proprietary software ACD/Labs v12.00. This QSAR is based on generally accepted simulation software the use of which has been published in peer-reviewed literature. Furthermore, the software takes into account the very low pKa of PFPA, its tendency to dissociate to perfluoropropionate anion at environmentally relevant pH, and the impact of speciation on distribution in aquatic systems. Log D as a function of pH is determined using a linear regression equation relating Log D to Log P, microspeciation of the simulated chemical and estimated log P of the microspecies. The use of pH adjustment for ionizable compounds is the most accurate approach currently feasible for estimation of partitioning characteristics. Therefore, we believe that this software is scientifically valid. In addition, the software's training set contains a number of chemicals with perfluorinated ethyl or ethylene groups, as well as perfluoropropyl and perfluorobutyl compounds, and in particular includes the ethyl ester of the test substance, and the test substance is therefore within the applicability domain of the model (see associated QPRF).  PFPA's estimated pKa of 0.38 is very close to the measured value of 0.34, indicating that the chemical will be entirely dissociated to an anionic form at pH > ca. 3. Therefore, this study is classified as acceptable as a QSAR simulation of pH-dependent log P, which is a relevant parameter for determination of transport and distribution of chemicals in the environment.  

 

In a previous chemical registration submission, a log P of 2.79 was reported for PFPA. This value is based on simulation using a non-applicable model in an obsolete version. It is classified as not reliable and is not considered further.