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Physical & Chemical properties

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
Justification for type of information:
For justification of read-across see endpoint summary
Reason / purpose:
read-across source
Dissociating properties:
yes
No.:
#1
pKa:
1.3
Temp.:
25 °C
Remarks on result:
other: The result is based on QSAR prediction at ambient temperature.
No.:
#2
pKa:
2
Temp.:
25 °C
Remarks on result:
other: The result is based on QSAR prediction at ambient temperature.
No.:
#3
pKa:
3.4
Temp.:
25 °C
Remarks on result:
other: The result is based on QSAR prediction at ambient temperature.
No.:
#4
pKa:
4.1
Temp.:
25 °C
Remarks on result:
other: The result is based on QSAR prediction at ambient temperature.
No.:
#5
pKa:
5.9
Temp.:
25 °C
Remarks on result:
other: The result is based on QSAR prediction at ambient temperature.
No.:
#6
pKa:
6.6
Temp.:
25 °C
Remarks on result:
other: The result is based on QSAR prediction at ambient temperature.
No.:
#7
pKa:
8
Temp.:
25 °C
Remarks on result:
other: The result is based on QSAR prediction at ambient temperature.
No.:
#8
pKa:
> 10
Temp.:
25 °C
Remarks on result:
other: The result is based on QSAR prediction at ambient temperature.
Endpoint:
dissociation constant
Type of information:
(Q)SAR
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: This is an accepted calculation method supported by a limited amount of additional validation.
Justification for type of information:
See attached document
Principles of method if other than guideline:
Predictive method
GLP compliance:
no
Dissociating properties:
yes
No.:
#1
pKa:
1.3
Temp.:
25 °C
Remarks on result:
other:
Remarks:
The result is based on QSAR prediction at ambient temperature.
No.:
#2
pKa:
2
Temp.:
25 °C
Remarks on result:
other:
Remarks:
The result is based on QSAR prediction at ambient temperature.
No.:
#3
pKa:
3.4
Temp.:
25 °C
Remarks on result:
other:
Remarks:
The result is based on QSAR prediction at ambient temperature.
No.:
#4
pKa:
4.1
Temp.:
25 °C
Remarks on result:
other:
Remarks:
The result is based on QSAR prediction at ambient temperature.
No.:
#5
pKa:
5.9
Temp.:
25 °C
Remarks on result:
other:
Remarks:
The result is based on QSAR prediction at ambient temperature.
No.:
#6
pKa:
6.6
Temp.:
25 °C
Remarks on result:
other:
Remarks:
The result is based on QSAR prediction at ambient temperature.
No.:
#7
pKa:
8
Temp.:
25 °C
Remarks on result:
other:
Remarks:
The result is based on QSAR prediction at ambient temperature.
No.:
#8
pKa:
> 10
Temp.:
25 °C
Remarks on result:
other:
Remarks:
The result is based on QSAR prediction at ambient temperature.

HMDTMP was determined to have eight pKa values, of: 
1.3
2
3.4
4.1
5.9
6.6

8

>10

Conclusions:
HMDTMP acid was determined to have eight dissociation constant using a relevant estimation method.

Description of key information

Dissociation constant (HMDTMP-xK): HMDTMP acid has eight ionisable phosphonate groups.

Key value for chemical safety assessment

Additional information

In aqueous solution, HMDTMP-xK will ionise to form HMDTMP acid and potassium ion. Dissociation constant are obtained for the salt by valid read-across from the parent acid. Eight dissociation constants as listed below were obtained for the parent acid using an appropriate estimation method. The result is considered reliable and selected as key study.

pKa 1 = 1.3
pKa 2 = 2
pKa 3 = 3.4
pKa 4 = 4.1
pKa 5 = 5.9
pKa 6 = 6.6

pKa 7 = 8

pKa 8 = >10

Similarly, in an available secondary source to which reliability could not be assigned, six dissociation constant values as listed below are reported for the substance.

pKa 1 = 3.25 
pKa 2 = 5.12 
pKa 3 = 5.68
pKA 4 = 6.23 
pKa 5 = 7.71 
pKa 6 = 11.82

 

An approximate experimental determination, using stocichiometric titration and pH determination of aqueous solutions, has been conducted. This is considered to provide suitable and practical information, which is fit for purpose in the context of REACH chemical safety assessment. This data is reported in section 4.20.