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Physical & Chemical properties

Dissociation constant

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Description of key information

As generally dissociating properties of salts cannot be estimated by the program, estimation results of the parent acid 2-phosphonobutane-1,2,4-tricarboxylic acid are taken into account for this endpoint. The dissociation constants for 2-phosphonobutane-1,2,4-tricarboxylic acid are estimated to be pKa1 of 8.59, pKa2 of 4.99, pKa3 of 4.44, pKa4 of  3.99 and pKa5 of 1.08 indicating that this substance presents mainly as ionic form under environmentally relevant pH 5 - 9.

Key value for chemical safety assessment

Additional information

The calculation of the dissociation constants of 2-phosphonobutane-1,2,4-tricarboxylic acid in water was performed by software ACD ChemSketch ACD/Labs 7.00 Release, Product Version 7.05. Usually the resulting dissociation constants are calculated for 20°C.

2-phosphonobutane-1,2,4-tricarboxylic acid in water can release 5 protons step by step.

Each release is described by one equilibrium reaction or equilibrium constant (pKa):

1. pKa (HL = H+L) = 8.59 ± 0.50

2. pKa (H2L = H+HL) = 4.99 ± 0.14

3. pKa (H3L = H+H2L) = 4.44 ± 0.10

4. pKa (H4L = H+H3L) = 3.99 ± 0.21

5. pKa (H5L = H+H4L) = 1.08 ± 0.42

Depending on the pKa value, the acid dissociation constants indicate strong (pKs < 3.8), medium strong (pKs < 7.2) and weak (pKs < 16) acids.

The pKa values indicate neither very strong nor very weak acids.