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Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Study period:
March - May 2008
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
test item is unstable in water, therefore the hydrolysis product PMA was tested; refer to analogue justification provided in IUCLID section 13
Qualifier:
according to
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
- Description: white powder
- Batch number: 8M30N
- Storage conditions: room temperature in the dark upto 04 April 2008, thereafter at approximately 4 °C, over silica gel, in the dark
Dissociating properties:
yes
No.:
#1
pKa:
2.18
Temp.:
25 °C
No.:
#2
pKa:
2.7
Temp.:
25 °C
No.:
#3
pKa:
4.4
Temp.:
25 °C
No.:
#4
pKa:
5.45
Temp.:
25 °C
Conclusions:
The dissociation constants of the four carboxylic acid functional groups at 25°C were determined by potentiometric titration to be 2.18, 2.70, 4.40 and 5.45 respectively.
Executive summary:

The dissociation constants of the carboxylic acid functional groups of the test material were determined by potentiometric titration, Method 112 of the OECD Guidelines. The dissociation constants of the four carboxylic acid functional groups at 25°C were determined by potentiometric titration to be 2.18, 2.70, 4.40 and 5.45 respectively.

Description of key information

As the substance to be registered, PMDA, is unstable in water, the corresponding hydrolysis product Pyromellitic acid (PMA) was tested. The dissociation constants of the carboxylic acid functional groups of the test material were determined by potentiometric titration. The dissociation constants of the four carboxylic acid functional groups at 25°C were determined by potentiometric titration to be 2.18, 2.70, 4.40 and 5.45 respectively.

Key value for chemical safety assessment

pKa at 20°C:
5.45

Additional information

Source: GLP-report