Registration Dossier

Physical & Chemical properties

Dissociation constant

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Description of key information

Trifluoroacetic acid has a very low dissociation constant, indicating that the substance will exist primarily under its ionised form.

Key value for chemical safety assessment

pKa at 20°C:
0.43

Additional information

The publication of Strehlow 1990, despite good reliability assigned, could not be used directly as the experimental work determined the thermodynamical equilibrium (dissociation) constant, and not the (p)Ka, and similarly for Kortum's handbook 1961 (citing Henne and Fox 1951). Nevertheless, both references are cited in the publication of Bowden 1996, which discusses published work on TFA dissociation constant, and are retained with a third value to adopt a mean pKa value of 0.47. For the purpose of the present dossier, the Merck index (reference handbook) value of pKa=0.3 will also be taken into account; the key value is calculated as the mean of Bowden's value, with a weight coefficient of 3, and Merck's value: (0.47*3 + 0.3)/4.