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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:
April 8 1997
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Qualifier:
no guideline required
Principles of method if other than guideline:
The estimation methods as described in the literature make pKa predictions based on the molecular structures of compounds.
The dissociation constant of an organic acid (or conjugated acid of an organic base) can be estimated by applying a linear free energy relation ship. At a constant temperature the pKa of a molecule is linear related to the free energy change for the reaction of ionisation of a proton.
GLP compliance:
no
Specific details on test material used for the study:
Colour: Orange-brown
Aggregate State at Room Temperature: Solid
Solubility in Water: about 50 g/l (20 °C)
Molecular Weight: 772.7 g/mol (H-form)
Dissociating properties:
yes
No.:
#1
pKa:
-5
Remarks on result:
other: sulfuric acid 1
No.:
#2
pKa:
-6.3
Remarks on result:
other: sulfonic acid 1
No.:
#3
pKa:
-5
Remarks on result:
other: sulfuric acid 2

The molecular structure of the acid form of FAT 45'176/A was used for the estimation of the dissociation behaviour. The test compound has various sites which can either be protonated or can dissociate.

Conclusions:
The behaviour of FAT45'176/A in aqueous solutions is dominated by the strongly acidic -SO3H- and -SO4H- groups. The molecule is 3-fold negatively charged and is present in anionic form over the whole environmentally relevant pH range.
Executive summary:

The molecular structure of the main component of FAT45'176/A was used for the estimation of the dissociation behaviour. The behaviour of FAT45'176/A in aqueous solutions is dominated by the strongly acidic -SO3H- and -SO4H- groups. The molecule is 3-fold negatively charged and is present in anionic form over the whole environmentally relevant pH range.

Description of key information

The behaviour of Reactive Orange 136 in aqueous solutions is dominated by the strongly acidic -SO3H- and -SO4H- groups. The molecule is 3-fold negatively charged and is present in anionic form over the whole environmentally relevant pH range.

Key value for chemical safety assessment

Additional information

The molecular structure of the main component of FAT45'176/A was used for the estimation of the dissociation behaviour. The behaviour of FAT45'176/A in aqueous solutions is dominated by the strongly acidic -SO3H- and -SO4H- groups. The molecule is 3-fold negatively charged and is present in anionic form over the whole environmentally relevant pH range.