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Dissociation constant

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Endpoint:
dissociation constant
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Justification for type of information:
See IUCLID section 13 for read across justification
Reason / purpose for cross-reference:
read-across source
Principles of method if other than guideline:
The use of secondary sources of data is acceptable when they are based on a critical evaluation of peer-reviewed data and a consequent selection of a reliable and representative value for the property under investigation. The introduction to the Merck Index states that physical data are cited as found in the literature. When several alternate data values appear in the literature, the data are evaluated and representative selections are made; values are then reported with the corresponding source. Therefore, although the method used is not known, the values presented here are acceptable as they are from a reliable secondary source of physico-chemical data.
GLP compliance:
not specified
Dissociating properties:
yes
No.:
#1
pKa:
4.41
Temp.:
25 °C
No.:
#2
pKa:
5.28
Temp.:
25 °C
Conclusions:
The dissociation constants (pKa) of adipic acid are 4.41 and 5.28.
Executive summary:

The dissociation constants (pKa) of adipic acid are 4.41 and 5.28. No information on the test methods used is available in the publication (O'Neil 2006). However, this information is taken from a peer reviewed handbook and can be considered adequate for use for this endpoint.

These results have been read across to dilithium adipate as the substance is a metal salt of a dicarboxylic acid and aqueous solutions of the substance would be expected to dissociate to free metal ions and carboxylic acid ions. The carboxylic acid ions would then be expected to achieve acid-base equilibrium, depending on the pKa of the carboxylic acid, at the pH of the solution. The dissociation constant of the lithium salt is therefore effectively represented by the dissociation constant(s) of the relevant carboxylic acid, as the ionisable moiety.

Endpoint:
dissociation constant
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Justification for type of information:
See IUCLID section 13 for read across justification
Reason / purpose for cross-reference:
read-across source
Principles of method if other than guideline:
The use of secondary sources of data is acceptable when they are based on a critical evaluation of peer-reviewed data and a consequent selection of a reliable and representative value for the property under investigation. The introduction to the Merck Index states that physical data are cited as found in the literature. When several alternate data values appear in the literature, the data are evaluated and representative selections are made; values are then reported with the corresponding source. Therefore, although the method used is not known, the values presented here are acceptable as they are from a reliable secondary source of physico-chemical data.
GLP compliance:
not specified
Dissociating properties:
yes
No.:
#1
pKa:
4.53
Temp.:
25 °C
No.:
#2
pKa:
5.33
Temp.:
25 °C
Conclusions:
The dissociation constants (pKa) of azelaic acid are 4.53 and 5.33 at 25°C.
Executive summary:

The dissociation constants (pKa) of azelaic acid are 4.53 and 5.33 at 25°C. No information on the test methods used is available in the publication (O'Neil 2006). However, this information is taken from a peer reviewed handbook and can be considered adequate for use for this endpoint.

These results have been read across to dilithium azelate as the substance is a metal salt of a dicarboxylic acid and aqueous solutions of the substance would be expected to dissociate to free metal ions and carboxylic acid ions. The carboxylic acid ions would then be expected to achieve acid-base equilibrium, depending on the pKa of the carboxylic acid, at the pH of the solution. The dissociation constant of the lithium salt is therefore effectively represented by the dissociation constant(s) of the relevant carboxylic acid, as the ionisable moiety.

Endpoint:
dissociation constant
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Justification for type of information:
See IUCLID section 13 for read across justification
Reason / purpose for cross-reference:
read-across source
Principles of method if other than guideline:
The use of secondary sources of data is acceptable when they are based on a critical evaluation of peer-reviewed data and a consequent selection of a reliable and representative value for the property under investigation. The introduction to the Merck Index states that physical data are cited as found in the literature. When several alternate data values appear in the literature, the data are evaluated and representative selections are made; values are then reported with the corresponding source. Therefore, although the method used is not known, the values presented here are acceptable as they are from a reliable secondary source of physico-chemical data.
GLP compliance:
not specified
Dissociating properties:
yes
No.:
#1
pKa:
4.59
Temp.:
25 °C
No.:
#2
pKa:
5.59
Temp.:
25 °C
Conclusions:
The dissociation constants (pKa) of sebacic acid are 4.59 and 5.59.
Executive summary:

The dissociation constants (pKa) of sebacic acid are 4.59 and 5.59. No information on the test methods used is available in the publication (O'Neil 2006). However, this information is taken from a peer reviewed handbook and can be considered adequate for use for this endpoint.

These results have been read across to dilithium sebacate as the substance is a metal salt of a dicarboxylic acid and aqueous solutions of the substance would be expected to dissociate to free metal ions and carboxylic acid ions. The carboxylic acid ions would then be expected to achieve acid-base equilibrium, depending on the pKa of the carboxylic acid, at the pH of the solution. The dissociation constant of the lithium salt is therefore effectively represented by the dissociation constant(s) of the relevant carboxylic acid, as the ionisable moiety.

Description of key information

The dissociation constants of the substances in the lithium salts of dicarboxylic acids category have been read across from the respective acids. The acids have measured pKA1 values of 4.41, 4.53 and 4.59 and measured pKA2 values of 5.28, 5.33 and 5.59, respectively for adipic acid, azelaic acid and sebacic acid (O’Neil 2006). These values are relatively low, therefore these dicarboxylate substances are expected to be in the acid (anionic) form at environmental pH. This is supported by the experimental data on dilithium glutarate (C5) which gives a pKa of 4.7 (see dissemination portal).

Key value for chemical safety assessment

Additional information

No data are available for the dissociation constant of the substances. The substances are all lithium salts of dicarboxylic acids. Aqueous solutions of the substances are therefore expected to dissociate to free metal ions and carboxylic acid ions. The carboxylic acid ions would then be expected to achieve acid-base equilibrium, depending on the pKA of the carboxylic acid, at the pH of the solution. The dissociation constant of the substance is effectively represented by the dissociation constant(s) of the relevant carboxylic acid, as the ionisable moiety. Therefore, this data requirement has been completed using data on the dissociation of the carboxylic acids. Reliable measured data available in the published literature for dicarboxylic acids have been used to complete this endpoint.