Climbazole

Dissociation constant

Description of key information

The pKa values of the test item were determined to be 5.2 and 10.9 at 20°C.

Key value for chemical safety assessment

pKa at 20°C:

5.2

Additional information

The dissociation potential of the test item was investigated according to the procedures described in the OECD guideline 112. In a first step the dissociation constants were determined using the spectrometric method (project CSL-13-0680.01). Since no isosbestic point could be observed, and the spectra showed no continuous trend from the ionized to the unionized forms, the spectrometric method is not suitable to determine the dissociation constant of the test item. Therefore, a further test was carried out using the titration method. Considering the low solubility of the test item, a small amount of a water-miscible solvent was used to prepare the test solution. However, the organic solubilizer influenced the pH value of the test item solution significantly (decreased by about one unit). Thus, the test was rated with RL 3 and an additional test was performed using the titration method without any solvent. Without any solvent the pH values before titration were constant at 20°C. The dissociation constant values were determined to be 5.2 and 10.9 at 20° C. Since the test performance was reliable (RL 2) these results were used for the assessment and no further tests were conducted.