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Dissociation constant

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dissociation constant
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The dissociation constant is not determined. As indicated in the ECHA Endpoint Specific Guidance (R.7.a): "..... for complex mixtures (e.g. UVCBs) containing ionisable components the assessment of pKa is clearly complicated. Estimation of the individual components' pKa values, if appropriate, should be considered." As the test substance is an UVCB with several compounds containing ionizable groups a single pKa cannot be defined. When calculating the pKa of individual components with the pKa module of the on-line calculator SPARC (September 2009), pKa values appear to be mostly outside the pH range relevant for the environment as well as the biologically relevant pH range (incl pH 1-2 for the stomach). Some pKa values however are in the relevant pH range (4-[(2-aminoethoxy)ethyl]morpholine: pKa = 5.92 (ring N); 3-morpholinone: pKa = 11.48 (N); also reference is made to Butler and White, 2010, who also calculated pKa values for some individual components) and thus some ionization should be accounted for. The different Koc values obtained at different pH values, might result from ionization.

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