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EC number: 215-925-7 | CAS number: 1453-58-3
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:
- 2013-04-22 - 2013-06-07
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- guideline study
- Qualifier:
- according to guideline
- Guideline:
- OECD Guideline 112 (Dissociation Constants in Water)
- Deviations:
- yes
- Remarks:
- The concentration of the test item solution was 1 mol/L instead of maximal 0.01 mol/L. This was considered uncritical, as otherwise no dissociation constant could have been determined.
- GLP compliance:
- yes (incl. QA statement)
- Dissociating properties:
- yes
- No.:
- #1
- pKa:
- 3.436
- Temp.:
- 20 °C
- No.:
- #2
- pKa:
- 3.458
- Temp.:
- 20 °C
- No.:
- #3
- pKa:
- 3.456
- Temp.:
- 20 °C
- Conclusions:
- The test item 3-Methylpyrazol should be considered as base with one proton acceptor unit. The corresponding acid has a pKa of 3.450 ± 0.012 at 20.0 ± 0.1°C.
Therefore, the pKb of 3-Methylpyrazol is stated as 10.550 ± 0.012 at 20.0 ± 0.1°C. - Executive summary:
The dissociation constant of 3-Methylpyrazol was determined using the titrimetric method in an aqueous solution of the test item containing 1 mol/L according to OECD guideline 112. The measurements were performed at 20.0 ± 0.1 °C. From the titration curves, one dissociation constant could be determined. The three main determinations showed good correlation.
As a titration using NaOH yielded no points of equivalence, it can be considered that the test item contain no acidic NH.
The test item 3-Methylpyrazol should be considered as base with one proton acceptor unit. The corresponding acid has a pKaof 3.450 ± 0.012 at 20.0 ± 0.1°C.
Therefore, the pKbof 3-Methylpyrazol is stated as 10.550± 0.012 at 20.0 ± 0.1°C.
Reference
Values Determination of pKafirst Measurement
Volume HCl in mL |
pH |
19.686 |
3.441 |
19.786 |
3.436 |
19.886 |
3.432 |
19.986 |
3.427 |
Values Determination of pKasecond Measurement
Volume HCl in mL |
pH |
19.352 |
3.466 |
19.452 |
3.462 |
19.552 |
3.456 |
19.652 |
3.452 |
Values Determination of pKathird Measurement
Volume HCl in mL |
pH |
19.547 |
3.462 |
19.647 |
3.457 |
19.747 |
3.453 |
19.847 |
3.448 |
Description of key information
The dissociation constant of 3-Methylpyrazol was determined using the titrimetric method in an aqueous solution of the test item containing 1 mol/L. The measurements were performed at 20.0 ± 0.1 °C. From the titration curves, one dissociation constant could be determined. The three main determinations showed good correlation.
As a titration using NaOH yielded no points of equivalence, it can be considered that the test item contain no acidic NH.
The test item 3-Methylpyrazol should be considered as base with one proton acceptor unit. The corresponding acid has a pKaof 3.450 ± 0.012 at 20.0 ± 0.1°C.
Therefore, the pKbof 3-Methylpyrazol is stated as 10.550± 0.012 at 20.0 ± 0.1°C.
Key value for chemical safety assessment
- pKa at 20°C:
- 3.45
Additional information
Data obtained from a guideline study according to OECD 112 with GLP and therefore considered reliable without restrictions.
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