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Physical & Chemical properties

Dissociation constant

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Description of key information

Dissociation constant of methyl 4-hydroxybenzoate:
pKa = 8.4 (OECD Guideline No. 112)
Literature data: pKa = 8.4 - 8.87

Key value for chemical safety assessment

pKa at 20°C:
8.4

Additional information

Sodium methylparaben is the sodium salt of the corresponding acid methyl 4-hydroxybenzoate. Depending on the pH both species are convertable into each other. The pKa is only defined for the corresponding acid and is related to the dissociation of the hydroxylic function. Thus the dissociation constant needs to be reported for the corresponding acid methyl 4-hydroxybenzoate only.

The dissociation constant of methyl 4-hydroxybenzoate was determined in a GLP study by means of a spectral photometric method according to OECD-Guideline No. 112 to be pKa = 8.4 (standard deviation = 0.1).

The experimental result is supported by literature data.