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Dissociation constant

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Endpoint:
dissociation constant
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
2014
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
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 14.0 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 © 2009-2012; Build: 2254
GLP compliance:
no
Dissociating properties:
yes
No.:
#1
pKa:
11.3
Temp.:
25 °C
Remarks on result:
other: (Atom number: 17)
No.:
#2
pKa:
12
Temp.:
25 °C
Remarks on result:
other: (Atom number: 16)

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

2. Unambiguous algorithm: For 6.6`-Di-tert.-butyl-2.2`-methylenedi-p-cresol the following fragment descriptors (parent compound) were identified as reaction centres: HO-Cring-R and R-Cring-OH

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 57 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 6.6'-Di-tert.-butyl-2.2'-methylenedi-p-cresol

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 6.6`-Di-tert.-butyl-2.2`-methylenedi-p-cresol 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 6.6`-Di-tert.-butyl-2.2`-methylenedi-p-cresol were estimated to be pKa1 of 11.3 (Atom number: 17 and pKa2 of 12.0 (Atom number: 16).
Executive summary:

The dissociation constants of 6.6`-Di-tert.-butyl-2.2`-methylenedi-p-cresol were estimated by ACD/pKa DB included in ACD/Percepta 14.0.0 (Build 2254) and showed a pKa1 of 11.3 (Atom number: 17) and pKa2 of 12.0 (Atom number: 16). According to the estimated results, this substance presents mainly as ionic form under environmentally relevant pH 5 - 9.

Endpoint:
dissociation constant
Type of information:
(Q)SAR
Adequacy of study:
key study
Study period:
2010
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
The pKa value for DMBC/Vulkanox was calculated with the programme SPARC as recommended in the REACH Guidance on information requirements and chemical safety assessment, Chapter R.7.1.17.3, Table R.7.1-36. The resulting value is not an experimental one but estimated with a QSAR calculation and therefore reliable with restrictions.
Justification for type of information:
QSAR prediction
Reason / purpose:
reference to same study
Reason / purpose:
reference to other study
Qualifier:
no guideline followed
Principles of method if other than guideline:
Calculation by using SPARC Performance Automated Reasoning in Chemistry (V 4.5).
GLP compliance:
no
Dissociating properties:
no
No.:
#1
pKa:
11.55

No remarks

Conclusions:
The dissociation constant pKa of DBMC/Vulkanox was calculated to be 11.55.
Executive summary:

By using SPARC Performance Automated Reasoning in Chemistry (V 4.5) the dissociation constant pKa of DBMC/Vulkanox was calculated to be 11.55. In accordance to the REACH Guidance on information requirements and chemical safety assessment, Chapter R.7.1.17, the pKa value is > 10, thus DBMC does not tend to dissociate in water under normal environmental conditions.

Description of key information

The dissociation constants for 6.6`-Di-tert.-butyl-2.2`-methylenedi-p-cresol were estimated to be pKa1 of 11.3 (Atom number: 17) and pKa2 of 12.0 (Atom number: 16).

Key value for chemical safety assessment

pKa at 20°C:
11.3

Additional information