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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Physical & Chemical properties

Dissociation constant

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Administrative data

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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:

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.