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Physical & Chemical properties

Dissociation constant

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Description of key information

Dissociation constants (trimellitic acid): pKa1= 2.91, pKa2= 3.94, pKa3= 5.30 at 20 ± 1 °C.

Key value for chemical safety assessment

pKa at 20°C:
2.91

Additional information

A waiver is proposed for the parent monomer on the basis that trimellitic anhydride hydrolyses almost instantaneously on contact with water and measurement of its dissociation constant(s) is therefore not technically feasible.

Dissociation constants are, however, available for trimellitic acid (TMLA), the hydrolysis product of trimellitic anhydride. At 20 degrees C, the pKa1, pKa2 and pKa3 values of TMLA are 2.91, 3.94 and 5.30, respectively.

The species distribution generated by the dissociation of this acid was determined, according to these constants, as function of pH.