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Physical & Chemical properties

Dissociation constant

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Description of key information

Dissociation constant.001: pKa values calculated for organic phase samples at pH 9.5 and 10.0 were 9.37 and 9.43, respectively, with a mean pKa of 9.40 and a mean Ka of 3.98 x 10^-10.
Dissociation constant.002: The pKa values of TBBPA are reported in a WHO document to be 7.5 and 8.5.

Key value for chemical safety assessment

pKa at 20°C:
9.4

Additional information

In a GLP/Guideline-compliant study (Dissociation constant.001),the dissociation constant (pKa) of TBBPA was determined to be 9.40.

The direct titration method typically used for determining the dissociation constant K was not suitable for TBBPA due to its extremely low aqueous solubility. An alternative method developed at the testing facility was employed. The test substance was purified by normal phase HPLC with fraction collection to obtain the purest available form of the test material as specified in the guideline. Test solutions, each containing 50 µg/L nominal concentration of TBBPA, were prepared over the pH range 6.0 to 12.0 at 0.5 pH intervals.

Both the dissociated and undissociated components of TBBPA were determined for each test solution by HPLC with ultraviolet detection.