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Physical & Chemical properties

Dissociation constant

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Description of key information

Under the conditions of this study the pKa values were determined to be 4.03 and 6.69 at 20 °C.

Key value for chemical safety assessment

Additional information

The dissociation constant of the test material was evaluated in a study conducted in accordance with the standardised guideline OECD 112 under GLP conditions. The study was awarded a reliability score of 1 in accordance with the criteria for assessing data quality set forth by Klimisch et al. (1997).

The test method used was the titration method. As a 0.01 M solution of the test material is 2.108 g/L, which is above the stated solubility value of 0.3 g/L, a concentration of nominally 0.15 g/L (half the stated water solubility) was used.

The pH of the test solution in double distilled water was about 8. On this basis, two preliminary titrations were performed, one with 0.01 M HCl and the other with 0.01M NaOH. The double distilled water was considered to be free of dissolved carbon dioxide.

A graph to cover both titrations was constructed. The end point of the acid titration was taken to be the starting point. The descending volumes of acid from the end point were subtracted from the end point volume and the end point volume of acid was added to the alkali volumes. Two inflections were revealed, indicative of two pKa values.

Two definitive tests were performed in like manner.

Under the conditions of this study the pKa values were determined to be 4.03 and 6.69 at 20 °C.