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Physical & Chemical properties

Dissociation constant

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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.