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Physical & Chemical properties

Dissociation constant

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Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
other: Non-guideline, experimental method.
Reason / purpose:
reference to same study
Qualifier:
no guideline followed
Principles of method if other than guideline:
Retention time is measured in a series of methanol gradient elutions, with varing pH and duration, on a reverse-phase HPLC column. Models describing the variations and their dependence on dissociation constants and partition coefficients were derived.
GLP compliance:
no
Dissociating properties:
yes
No.:
#1
pKa:
8.79
Temp.:
25 °C
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
other: Non-guideline study.
Reason / purpose:
reference to same study
Qualifier:
no guideline followed
Principles of method if other than guideline:
The UV absorption spectrum was measured at varing pH. Absorption bands were identified which were associated with the neutral and dissociated forms, which allowed the pKa to be derived.
GLP compliance:
no
Dissociating properties:
yes
No.:
#1
pKa:
8.37
Temp.:
20 °C
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
other: No experimental detail provided.
Reason / purpose:
reference to same study
Qualifier:
no guideline followed
Principles of method if other than guideline:
According to Clarke, F.H., J. Pharm. Sci., 1984, 73, 226-230: Differential titration and nonlinear curve-fitting.
GLP compliance:
no
Dissociating properties:
yes
No.:
#1
pKa:
8.1

Temperature not reported.

Description of key information

8.37, Edwards 1953
8.79, 25°C, Wiczling 2006
8.10, Berner 1989

Key value for chemical safety assessment

pKa at 20°C:
8.4

Additional information

Three verifiable experimental literature values for the pKa were found, none of which were considered to be reliable, mainly due to limited documentation of the experimental methods. The average of the three values was taken.