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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:
2017
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 14.01 software program for estimating the dissociation constant (pKa) in water. The fragment has been found in the Internal Reaction Centers Database with an experimental equation. The program was developed by Advanced Chemistry Development Inc.
90 Adelaide Street West, Toronto, Ontario, M5H 3V9, Canada (http://www.acdlabs.com); Copyright © 1994-2013; Build: 18 Sep 2013
GLP compliance:
no
Dissociating properties:
yes
No.:
#1
pKa:
>= 14.7 - <= 15.9
Temp.:
25 °C
Remarks on result:
other: HL/H+L

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

2. Unambiguous algorithm: For Menthol the following fragment descriptor (parent compound) was identified as reaction centre: HO-C-R

3. Applicable domain: The identified reaction center has been found as fragment in the Internal Reaction Centers Database with experimental equations. The substance only contains 31 atoms, which is much less than the limit of ACD/pKa DB of 255. The substance only contains one ionization centre 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 DL-Menthol applied by the program is verified by the user. The rules applied for the substance 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, 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 DL-Menthol falls 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 DL-Menthol is estimated to be pKa of 15.3+-0.6
Executive summary:

The dissociation constant of DL-Menthol was estimated by ACD/pKa DB included in ACD/labs 7.00 Release. 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 constant of DL-Menthol was estimated by ACD/pKa DB included in ACD/labs 7.00 Release. According to the estimated result, this substance presence mainly as non-ionic form unter environmentally relevant pH 5 - 9.

Key value for chemical safety assessment

pKa at 20°C:
15.3

Additional information

The reported value refers to a temperature of 25 °C.