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EC number: 457-330-7 | CAS number: 66034-17-1
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:
- 24 February - 12 March 2004
- 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:
- May 1981
- Deviations:
- no
- GLP compliance:
- yes (incl. QA statement)
- Dissociating properties:
- not determined
- No.:
- #1
- pKa:
- 5.5
- Temp.:
- 20 °C
- Remarks on result:
- other: capillary electrophoresis method; piperazine
- No.:
- #2
- pKa:
- 9.8
- Temp.:
- 20 °C
- Remarks on result:
- other: capillary electrophoresis method; piperazine
- Conclusions:
- The two pKa's of piperazine were 9.8 and 5.5.
The pKa of pyrophosphate could not be determined.
It is planned to further investigate possible dissociation of T-1063FM.
Reference
Standardization titrants:
0.1 M NaOH
Equivalence points 0.523 and 0.520 ml
Molarity: 0.0495 N/0.522 ml=0.0950 M
0.1 M HCl
Equivalence points 0.660 and 0.660 ml
Molarity: 0.0499 N/0.660 ml=0.0756 M
Titration method:
Clear equivalence points were observed at approximately 1.150 ml and 2.450 ml of NaOH solution added. The calculated pKa1, pKa2, pKa3, pKa4and pKa5values are presented in Tables 1 and 2 in attachment "T-1063FM - results dissociation constant.pdf".
Capillary Electrophoresis method:
Table 3 (attachment "T-1063FM - results dissociation constant.pdf") shows the electrophoretic mobility of piperazine at different pH values. Piperazine has two basic nitrogen atoms and therefore two pKa values. One pKa can be found at the pH where the dissociation charge is 0.5, the other pKa can be found where the dissociation charge is 1.5. From the table it can be deduced that the two pKa's of piperazine are 9.8 and 5.5.
Description of key information
Only the pKa of the organic component piperazine could be determined. For the inorganic component pyrophosphate literature values are reported (OECD guideline 112).
Key value for chemical safety assessment
Additional information
Two methods (titration and capillary electrophoresis) were applied, however none of these methods was suitable to determine the pKa of the test substance as a whole. The titration method is hampered because pyrophosphate has buffering properties as well and capillary electrophoresis is not applicable for pyrophosphate.
Therefore only the pKa of the organic component piperazine could be determined. For the inorganic component pyrophosphate literature values are reported.
piperazine moiety:
pKa1= 5.5
pKa2= 9.8
pyrophosphate moiety*:
pKa1= 1.52
pKa2= 2.36
pKa3= 6.75
pKa4= 9.29
*: T. Hirokawa et al., J.Chromatogr., 271 (1983), D1-D106.
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