Registration Dossier

Physical & Chemical properties

Dissociation constant

Currently viewing:

Administrative data

Link to relevant study record(s)

Reference
Endpoint:
dissociation constant
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
2013
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Justification for type of information:
QSAR prediction
Guideline:
other: REACH guidance on QSARs R.6, May 2008
Deviations:
no
Principles of method if other than guideline:
ACD 7.0 software program for estimating the dissociation constant (pKa) in water.The recommended method, “apparent constants, approximated”, was used for the estimation. The program was developed by Advanced Chemistry Development Inc.
90 Adelaide Street West, Toronto, Ontario, M5H 3V9, Canada (http://www.acdlabs.com); Copyright © 1994-2003; Build: 18 April 2003
GLP compliance:
no
Dissociating properties:
yes
No.:
#1
pKa:
-0.6
Temp.:
25 °C
Remarks on result:
other: HL/H+L (side chain)

1. Defined endpoint: Dissociation constant (pKa) in water

2. Unambiguous algorithm: For the side chain of the substance the following fragment descriptors (parent compound) were identified as reaction centres:

side chain: The fragment has been found in the Internal Reaction Centers Database. The structure used for calculation of pKa fully covered examined structure.

3. Applicable domain: The identified reaction center has been found as fragments in the Internal Reaction Centers Database with estimated equation. The side chain calculated contains only 16 atoms, which is much less than the limit of ACD/pKa DB of 255. The substance/side chain only contains one ionization centre with one fragment. The substance does not contain the atoms, which are not accepted by ACD/pKa DB. The fragment that occur in the structure of the side chains applied by the program are verified by the user. The rules applied for the substance/side chain appear appropriate. An individual uncertainty for the investigated substance is not available.

4. Statistical characteristics: Each calculation from ACD/pKa DB is provided with its 95 % confidence interval and, if available, literature references with experimental results. The accuracy of calculations for simple structures is usually better than ±0.2 pKa units (for complex structures it is better than ±0.5 pKa units).

5. Mechanistic interpretation: The mechanistic basis of the model is the linear free energy relationship (LFER), which is an empirical correlation between the standard free energies of reaction or activation for two series of reactions, both subjected to the same variations in reactant structures or reaction conditions. As applied to the estimation of acid dissociation constants, the LFER is basically a substituent-effect approach.

6. Adequacy of prediction: The result for the side chains and as a conclusion also for the entire molecule fall within the applicability domain described above and the estimation rules applied for the substance appear appropriate. Therefore the predicted value can be considered reliable yielding a useful result for further assessment.

Conclusions:
The dissociation constant for the substance was estimated via an external side chain (sulfonic acid) which was used for calculation as the entire molecule of the substance was too large for the calculation. This chain is assumed to be the only dissociable region within the molecule and as a conclusion could be used to represent the dissociation behaviour of the entire molecule.
The following dissociation constant was estimated for the side chain:

Side chain (sulfonic acid):
pKa (HL/H+L) = -0.60 ± 0.50
Executive summary:

The dissociation constant for the substance was estimated via an external side chain (sulfonic acid) which was used for calculation as the entire molecule of the substance was too large for the calculation and is further not assumed to be present in its undissociated form as no ionization centers are available. This chain is assumed to be the only dissociable region within the molecule and as a conclusion could be used to represent the dissociation behaviour of the entire molecule.

The following dissociation constant was estimated for the side chain:

Side chain (sulfonic acid):

pKa (HL/H+L) = -0.60 ± 0.50

The dissociation constant of the substance was estimated by ACD/pKa DB included in ACD/labs 7.00 Release. According to the estimated results, the side chain (sulfonic acid) is mainly present in the deprotonated/dissociated form under environmentally relevant pH 5 - 9.

Description of key information

The dissociation constant for the substance was estimated via an external side chain (sulfonic acid) which was used for calculation as the entire molecule of the substance was too large for the calculation. This chain is assumed to be the only dissociable region within the molecule and as a conclusion could be used to represent the dissociation behaviour of the entire molecule.
The following dissociation constant was estimated for the side chain:
Side chain (sulfonic acid):
pKa (HL/H+L) = -0.60 ± 0.50

Key value for chemical safety assessment

Additional information

The dissociation constant for the substance was estimated via an external side chain (sulfonic acid) which was used for calculation as the entire molecule of the substance was too large for the calculation and is further not assumed to be present in its undissociated form as no ionization centers are available. This chain is assumed to be the only dissociable region within the molecule and as a conclusion could be used to represent the dissociation behaviour of the entire molecule.

The following dissociation constant was estimated for the side chain:

Side chain (sulfonic acid):

pKa (HL/H+L) = -0.60 ± 0.50

The dissociation constant of the substance was estimated by ACD/pKa DB included in ACD/labs 7.00 Release. According to the estimated results, the side chain (sulfonic acid) is mainly present in the deprotonated/dissociated form under environmentally relevant pH 5 - 9.