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Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
2015
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: accepted calculation method
Justification for type of information:
QSAR prediction
Guideline:
other: REACH guidance on QSARs R.6, May 2008
Principles of method if other than guideline:
ACD/Precepta 14.0.0 (Build 2254) 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 © 2012
GLP compliance:
no
Dissociating properties:
yes
No.:
#1
pKa:
-2.7
Temp.:
25 °C
Remarks on result:
other: (Atom number: 10)
No.:
#2
pKa:
-2
Temp.:
25 °C
Remarks on result:
other: (Atom number: 8)

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

2. Unambiguous algorithm: For 1,3-bis(3-methyl-2,5-dioxo-1H-pyrrolinylmethyl)benzene the following fragment descriptors (parent compound) were identified as reaction centres: R-NH+-R and R-NH+-C=O

3. Applicable domain: The identified reaction centers have been found as fragments in the Internal Reaction Centers Database with experimental equations. The substance only contains 40 atoms, which is much less than the limit of ACD/pKa DB of 255. The substance only contains two ionization centres with one fragment for each. The substance does not contain the atoms, what are not accepted by ACD/pKa DB. The fragment that occurs in the structure of 1,3-bis(3-methyl-2,5-dioxo-1H-pyrrolinylmethyl)benzene applied by the program is verified by the user. The rules applied for the substance appears 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, when 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 1,3-bis(3-methyl-2,5-dioxo-1H-pyrrolinylmethyl)benzene falls within the applicability domain described above and the estimation rulesapplied for the substance appears appropriate. Therefore the predicted value can be considered reliable yielding a useful result for further assessment.

Conclusions:
The dissociation constants for 1,3-bis(3-methyl-2,5-dioxo-1H-pyrrolinylmethyl)benzene are estimated to be pKa1 of -2.7 (Atom number: 10) and pKa2 of -2.0 (Atom number: 8).
Executive summary:

The dissociation constants of 1,3-bis(3-methyl-2,5-dioxo-1H-pyrrolinylmethyl)benzene were estimated by ACD/pKa DB included in ACD/Precepta 14.0.0 (Build 2254). According to the estimated results, this substance presents mainly as non-ionic form under environmentally relevant pH 5 - 9.

Description of key information

The dissociation constants for 1,3-bis(3-methyl-2,5-dioxo-1H-pyrrolinylmethyl)benzene are estimated to be pKa1 of -2.7 (Atom number: 10) and  pKa2 of -2.0 (Atom number: 8).

Key value for chemical safety assessment

pKa at 20°C:
-2

Additional information

The dissociation constants of 1,3-bis(3-methyl-2,5-dioxo-1H-pyrrolinylmethyl)benzene were estimated by ACD/pKa DB included in ACD/Precepta 14.0.0 (Build 2254). According to the estimated results, this substance presents mainly as non-ionic form under environmentally relevant pH 5 - 9.