Registration Dossier
Registration Dossier
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EC number: 243-001-3 | CAS number: 19372-44-2
Dissociation constant
Administrative data
Link to relevant study record(s)
Description of key information
The association constant of bis(pentane-2,4-dionato-O,O')calcium is log B11= 2.3 and pKa = 8.8 at 25°C.
Key value for chemical safety assessment
Additional information
Upon dissolution in water bis(pentane-2,4-dionato-O,O')calcium (CaL2, L = acetylacatonate) can in principle dissociate to CaL and the free metal ion Ca while the free ligand acetylacetone can be present as HL and L. The dissociation of bis(pentane-2,4-dionato-O,O')calcium is therefore dependent on pH.
From available literature data the following value is obtained for the association constant:
log B11= 2.3 and pKa= 8.8
where Bpq= [CapLq]/CapLq
At representative pH values, the relative distribution (%) of Ca species present in a solution of bis(pentane-2,4-dionato-O,O')calcium (CaL2) at [Ca]tot= 0.5 [L]tot= 0.06 M ([CaL2] = 7.9 g/l) as calculated with Hyperquad2008, using the above constants, is given the table below:
Ca species |
pH = 2 |
pH= 5 |
pH = 7 |
pH = 9 |
CaL2 |
0 |
0 |
0 |
0 |
CaL |
< 0.1 |
0.3 |
21.7 |
87.8 |
Ca |
> 99.9 |
99.7 |
78.3 |
12.2 |
The species CaL2does not exist in solution.
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