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Physical & Chemical properties

Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
2009
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Justification for type of information:
1. SOFTWARE
ACD/pKa

2. MODEL (incl. version number)
Not reported.

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
Not reported.

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
- Defined endpoint:
Calculation of accurate acid and base pKa constants (pKa = -logKa) under standard conditions (25°C and zero ionic strength) in aqueous solutions for every ionizable group within organic structures
Confidence intervals for all predicted pKa values, indicating their accuracy

- Unambiguous algorithm:
The algorithm uses Hammet-type equations and electronic substituent constants (σ) to predict pKa values for ionizable groups. Effects considered by the software include tautomeric equilibria, covalent hydration, and resonance effects in α, β-unsaturated systems.

Hammet-Type Equations—every ionizable group is characterized by several Hammet-type equations that have been parameterized to cover the most popular ionizable functional groups.

Sigma Constants—the internal training set contains >3000 derived experimental electronic constants. When the required substituent constant is not available from the experimental database, one of four algorithms are used to describe electronic effect transmissions through the molecular system.


5. APPLICABILITY DOMAIN
Not reported.

6. ADEQUACY OF THE RESULT
Required by REACH, Annex IX, 7.16.
Principles of method if other than guideline:
calculation using software ACD/pKa DB
GLP compliance:
no
Dissociating properties:
yes
No.:
#1
pKa:
ca. 13.23
Temp.:
25 °C
Conclusions:
The dissociation constant was calculated to be pKa= 13.2 at 25°C
Executive summary:

In this validated QSAR study (ACD/pKa DB), the dissociation constant of the test material (EC 213-426-9) was calculated to be pKa 13.2 at 25 ºC.

Description of key information

Validated QSAR suitable for the substance type.

Key value for chemical safety assessment

pKa at 20°C:
15.7

Additional information

The represented value was calculated using software ACD/pKa DB.

An additonal calculation using software SPARC yielded a value of pKa= 15.7 at 25°C

It can be suggested that an ionisable substance with a pKa above 10 will tend not dissociate in water under normal environmental conditions.