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Diss Factsheets

Physical & Chemical properties

Dissociation constant

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Administrative data

Link to relevant study record(s)

Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
Study completion date - 23 May 2005;
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
no guideline available
Principles of method if other than guideline:
Dissociation constant was calculated by the Hammett and Taft Correlations.
GLP compliance:
no
Specific details on test material used for the study:
Identity: FAT 40819/A
Appearance: solid/red brown gluey powder
Dissociating properties:
yes
No.:
#1
pKa:
3.7
Remarks on result:
other: Primary amine, method: Hammett
No.:
#2
pKa:
6.6
Remarks on result:
other: OH group in naphthol, method: Hammett
No.:
#3
pKa:
>= -8.7 - <= -6.4
Remarks on result:
other: Sulfonic acid groups (5x), method Hammett
No.:
#4
pKa:
0.4
Remarks on result:
other: Secondary amine (2x), method: Taft
No.:
#5
pKa:
>= -6.6 - <= -5.1
Remarks on result:
other: Triazine (3x), method: Hammett
No.:
#6
pKa:
ca. 0
Remarks on result:
other: Azobenzene, method: general estimation

The arenesulfonic acids are strong acids. In aqueous solutions they are completely dissociated.

It is not possible to estimate an exact value for the diazogroup, however, protonated azobenzenes are strong acids and therefore, the azo-group is normally not protonated in aqueous solutions.

Conclusions:
The behaviour of the test substance in aqueous solutions is dominated by the strongly acidic -SO3H-groups. Therefore, the molecule is negatively charged and is present in anionic form over the whole environmentally relevant pH range.
Executive summary:

The dissociation constant in water of the test substance was calculated using the Hammett and Taft Correlation methods and six pKa were estimated. The important pKa are from the strongly acidic -SO3H- groups. The test substance has dissociating properties because the molecule is negatively charged and is present in anionic form over the whole environmentally relevant pH range.

Description of key information

The dissociation constant in water of the test substance was calculated using the Hammett and Taft Correlation methods and six pKa were estimated. The important pKa are from the strongly acidic -SO3H- groups. The test substance has dissociating properties because the molecule is negatively charged and is present in anionic form over the whole environmentally relevant pH range.

Key value for chemical safety assessment

Additional information