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EC number: 428-040-8 | CAS number: 138261-41-3
Dissociation constant
Administrative data
Link to relevant study record(s)
- Endpoint:
- dissociation constant
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Study period:
- 13-24 Aug 2015
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- guideline study
- Qualifier:
- according to guideline
- Guideline:
- OECD Guideline 112 (Dissociation Constants in Water)
- Version / remarks:
- spectrophotometric method
- Qualifier:
- according to guideline
- Guideline:
- EPA OPPTS 830.7370 (Dissociation constants in water)
- Version / remarks:
- spectrophotometric method
- GLP compliance:
- yes (incl. QA statement)
- Remarks:
- Hess. Ministerium fur Umwelt, ländlichen Raum und Verbraucherschutz, Wiesbaden, Germany
- Dissociating properties:
- yes
- pKa:
- 11.8
- Temp.:
- 23 °C
- Endpoint:
- dissociation constant
- Type of information:
- experimental study
- Adequacy of study:
- supporting study
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- guideline study with acceptable restrictions
- Qualifier:
- according to guideline
- Guideline:
- OECD Guideline 112 (Dissociation Constants in Water)
- Version / remarks:
- titration method
- GLP compliance:
- yes
- Dissociating properties:
- ambiguous
- Temp.:
- 20 °C
- Remarks on result:
- not determinable
Referenceopen allclose all
Three individual experiments were carried out measuring the pH dependency of the UV/VIS spectra of the test item at room temperature (mean temperature 23 °C). The pKa-values were calculated according to the equations given in the above mentioned guidelines.
The UV/VIS spectra were recorded at pH values between pH 1.09 to
12.22.
The results of the experiments are summarized in the following table:
Experiment |
Concentration (1E-05 mol/L) |
pKa |
A |
3.90 |
11.86 |
B |
3.98 |
11.77 |
C |
4.00 |
11.84 |
Mean |
- |
11.82 (SD = 0.05) |
The pKa value for
each determination was calculated as the average of individual values
for which the dissociated portion laid between 10% and 90%. In each
series A, B, C 14 measurements were taken and measurements 5 -13 were
taken into account, data points for which the dissociated portion was
outside the given range were not used to calculate the final result.
The test substance demonstrated very weak basic properties.
Complete protonation could be achieved only in non-aqueous solvents in
presence of very strong acids. It
was not possible to specify a pK value of the
test substance in pure aqueous systems.
Description of key information
pKa: 11.8 at 23 °C (OECD 112, spectrophotometric method)
Key value for chemical safety assessment
Additional information
In an earlier experiment (OECD 112, titration method), the test substance demonstrated very weak basic properties. Complete protonation could be achieved only in non-aqueous solvents in presence of very strong acids. It was thus not possible to specify a pK value of the test substance in pure aqueous systems, and it was necessary to change the method applied.
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