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Physical & Chemical properties

Dissociation constant

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dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
2 (reliable with restrictions)
equivalent or similar to guideline
OECD Guideline 112 (Dissociation Constants in Water)
Principles of method if other than guideline:
This method utlilizes both the titration and conductometric titration methods. A known amount of the substance was titrated with a strong base (NaOH). The concentration of the neutralized acid was then increased by introducing step-wise aliquots of stock solution of the acid to the water. The conductivity of the solution was measured after each addition of stock solution.
GLP compliance:
Dissociating properties:
ca. 0.34
25 °C
Remarks on result:
other: PFPA's experimental pKa of 0.34 (Moroi et al, 2001) indicates that the chemical will be entirely dissociated to an anionic form at pH > ca. 3.
The pKa for PFPA was found to be 0.34.
Executive summary:

The acidity constants for a range of perfluoroalkanoic acids were determined by pH titration and by electric conductivity for acids with with 1 to 5 carbon atoms in the alkyl chain. The test was conducted at the Kyushu Sangyo University Department of Industrial Chemistry by Moroi Y, H Yano, O Shibata and T Yonemitsu. This study came from a publication of the Bulletin of the Chemical Society of Japan (74, 667-273 (2001)). This study was conducted using the tritration and conductometric titration methods.


Samples were obtained from Daikin Chemical Co. Ltd. Using the titration method, the pH was measured with a pH meter. The electrode was standardized at three different pHs of 1.680, 4.010, and 6.860 at 298.15 +/- 0.01 K. A 15 mL acid solution of known concentration was neutralized stepwise by introducing aliquots of a standardized NaOH solution. The titration was carried out under an inert atmosphere in order to protect it from atmospheric CO2. Then using the conductometric method, a glass tube containing 15 mL of purified water for conductivity measurement was set in a thermostat at 298.15 +/- 0.1 K. The concentration of the solution was increased stepwise by introducing aliquots of stock solution of the acid or its salt to the water. The conductivity of the solution was measured after each introduction.


An analytical procedure for titration and conductivity yielded a pKa for Titration 1 of 0.38 +/- 0.01, a pKa for Titration 2 of 0.34 +/- 0.04, and a pKa for Conductivity of 0.29 +/- 0.03 (see Table 1). pKa throughout the average of these results was 0.34. Therefore the pKa for PFPA is 0.34.


This study is classified as reliable with restrictions. While the study itself is robust and has been determined to be valid, it was not done under GLP. Also, the study did not follow a standard method, such as OECD. That said, the experimental result for pKa is relevant to the determination of this parameter because the methodology is very similar to the standard method of pKa determination and the result is consistent with the modeled value (0.38) that was estimated using Advanced Chemistry Development, Inc. (ACD/Labs) Toronto, Ontario, Canada. Version 12. The modeled value has been deemed valid because ACD is a software package that is based on generally accepted simulation software the use of which has been published in peer-reviewed literature. In addition, it contains several compounds in the training set that are analogous to the test substance. Therefore, this experimental value is classified as acceptable and relevant for determination of transport and distribution of this chemical in the environment.

Description of key information

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

Dissociation constant: 0.34 (pH titration and electric conductivity methods)

Key value for chemical safety assessment

pKa at 20°C:

Additional information