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Physical & Chemical properties

Dissociation constant

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dissociation constant
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
dissociation constant
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Study period:
15 Nov 2011
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
comparable to guideline study
equivalent or similar to guideline
other: SOP 00288 Version 1, corresponding to OECD Guideline 112, adopted May 1981
GLP compliance:
yes (incl. QA statement)
Ministerium für Umwelt und Naturschutz, Landwirtschaft und Verbraucherschutz des Landes Nordrhein-Westfalen
Dissociating properties:
20 °C

End neutralization point: 9.97 mL/pH 8.66

Half neutralization point: 4.98 mL/pH 4.04

pKa value: 4.00

(Half neutralisation point of the test item = pKa value)


With the software ACD/ChemSketch (ACD/Labs 7.00 Release), three values for the dissociation constant were calculated:

pKa (H3L/H+H2L) = 1.31 ± 0.50 (Isomer 2) and 1.68 ± 0.50 (Isomer 1) (Protonation of the NH fuction)

pKa (H2L/H+HL) = 3.57 ± 0.50 (Isomer 2) and 3.93 ± 0.50 (Isomer 1) (deprotonation of the OH-function and protonation of the NH-function)

pKa (HL/H+L) = 4.77 ± 0.19 (both isomers) (deprotonation of the second OH-function)

Due to the limitations of the experimental procedure, only one pKa was found. The titration method is able to measure pKa > 2. The other calculated pKa values are so close that the method cannot discriminate between them. Both pKa values are resolved in one pH-step.

Description of key information

Not applicable.

Key value for chemical safety assessment

Additional information

The substance Reaction mass of dipotassium 2-(3,4-dimethyl-1H-pyrazol-1-yl) succinate and dipotassium 2-(4,5-dimethy-1H-pyrazol-1-yl) succinate is a salt.

The dissociation constant of the 'parent substance' is given as supporting information, the pka of Reaction mass of 2-(3,4-dimethyl-1H-pyrazol-1-yl) succinic acid and 2-(4,5-dimethyl-1H-pyrazol-1-yl) succinic acid was determined according to internal standard operating procedure SOP 00288 v1, corresponding to OECD Guideline 112 (1981). The pka was determined to be 4.0 at 20 °C.