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Dissociation constant

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Description of key information

The UVCB substance 400160 consists of diester, monoester, and the diacid component. Out of these three components only the diacid and monoester are able to dissociate. The pKa of the diacid component is comparable to those of other long-chain fatty acids, e.g. oleic acid (calculated pKa 4.74 - SPARC On Line-Calculator, pKa 5.02 - literature value).

Key value for chemical safety assessment

Additional information

400160 is a surface active UVCB substance. For complex mixtures (e.g. UVCBs) containing ionisable components the assessment of pKa is technically challenging. The analytical method is not sensitive enough. As the analytical effort and costs to measure the dissociation constant of 400160 are not justified a weight of evidence approach was used instead of testing. Therefore the estimation of the ionisable component was considered.

The dissociation constant of the diacid component is similar to those of other long-chain fatty acids, e.g. oleic acid (pKa = 4.74 calculated for oleic acid using SPARC On-Line Calculator; pKa = 5.02 in aqueous solution at 25°C – literature value).

The compounds of 400160 which are able to dissociate have a pKa of around 5. Therefore the predicted pKa value matches the lower level of the environmental relevant pH margin (pH 5 -9). It is not expected that the predicted pKa value significantly differs from that value that could be obtained by testing.