Registration Dossier
Registration Dossier
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EC number: 237-860-3 | CAS number: 14024-63-6
Dissociation constant
Administrative data
Link to relevant study record(s)
- Endpoint:
- dissociation constant
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- guideline study
- Qualifier:
- according to guideline
- Guideline:
- OECD Guideline 112 (Dissociation Constants in Water)
- GLP compliance:
- no
- Dissociating properties:
- yes
- pKa:
- 8.8
- Temp.:
- 22 °C
- Conclusions:
- On dissolution of bis(pentane-2,4-dionato-O,O')zinc (ZnL2) in water, the predominant molecule in solution will be ZnL2 . On acidification ZnL2 dissociates to ZnL and HL and finally Zn. The fit to the experimental data calculates the association constants log β12 = 9.8 and log β11 = 5.
- Executive summary:
On dissolution of bis(pentane-2,4-dionato-O,O')zinc, batch no: 0928000125 (ZnL2), the predominant molecule in solution will be ZnL2 . On acidification ZnL2 dissociates to ZnL and HL and finally Zn. The fit to the experimental data calculates the association constants log β12 = 9.8 and log β11 = 5.2 but deviate from literature values which are on average on average log β12 = 8.08 and log β11 = 4.7.
The cause of deviation to the literature value is unknown and would require further investigation.
For this reason distribution plots were calculated from literature data, log β12 = 8.08, log β11 = 4.7, pKa = 8.8.
The relative distribution of Zn species at some discrete pH values, calculated from the literature data, is presented in Table 1.
Reference
Table 1: Relative distribution (%) of Zn species present in a solution of bis(pentane-2,4-dionato-O,O')zinc (ZnL2) at at [Zn] tot = 0.5 [L] tot = 0.06 M; ([ZnL2] = 7.9 g/l. Log β12 = 8.08, log β11 = 4.7, pKa = 8.8.
| Zn species | pH = 2 | pH = 5 | pH = 7 | pH = 9 |
| ZnL2 | 0 | 0.6 | 39.7 | 86.1 |
| ZnL | < 0.5 | 29.9 | 56.4 | 13.7 |
| Zn | > 99.5 | 69.4 | 3.8 | 0.1 |
Description of key information
On dissolution of bis(pentane-2,4-dionato-O,O')zinc (ZnL2) in water, the predominant molecule in solution will be ZnL2 . On acidification ZnL2 dissociates to ZnL and HL and finally Zn. The fit to the experimental data calculates the association constants log β12 = 9.8 and log β11 = 5.
Key value for chemical safety assessment
- pKa at 20°C:
- 8.8
Additional information
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