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Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Principles of method if other than guideline:
not stated
GLP compliance:
no
Dissociating properties:
yes
Remarks on result:
other: Acid-base constant: Acid-base-titration
No.:
#1
pKa:
1.7
Temp.:
25 °C
Remarks on result:
other: ± 0.2
No.:
#2
pKa:
2.47
Temp.:
25 °C
Remarks on result:
other: ± 0.04
No.:
#3
pKa:
7.28
Temp.:
25 °C
Remarks on result:
other: ± 0.06
No.:
#4
pKa:
10.29
Temp.:
25 °C
Remarks on result:
other: ±0.07

HEDP has four possible ionisations. In a recognised data source for information on pKa values and stability constants, pKa values of HEDP are reported of:

pKal = 1.7 
pKa2 = 2.47 
pKa3 = 7.28 
pKa4 = 10.29 

These were measured by titration in 0.1 M potassium chloride. The original source is cited in the data book. These data are from a recognised handbook.

Conclusions:
Dissociation constant values of 1.7, 2.47 , 7.28, 11.41 are reported at 25°C in a handbook which has been subject to peer-review and in which the original data sources are traceable. The result is considered to be reliable.

Description of key information

Dissociation constant: 1.7, 2.47, 7.28, 11.41  (4 values recorded) at 25°C

Key value for chemical safety assessment

Additional information

Dissociation constant values of 1.7, 2.47, 7.28, 11.41 are reported at 25°C in a handbook which has been subject to peer-review and in which the original data sources are traceable. The result (Martell 1968) is considered to be reliable and selected for key study.

Dissociation constant values of 1.35, 2.87, 7.03, 11.3 are reported in other secondary literature (Lacour 1999). They are considered as supporting studies.