disodium 4-amino-6-((4-((4-(2,4-diaminophenyl)azo)phenylsulfamoyl)phenyl)azo)-5-hydroxy-3-((4-nitrophenyl)azo)naphthalene-2,7-disulfonate

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

November 11, 2009-November 21, 2011

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Qualifier:

according to guideline

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

GLP compliance:

no

Dissociating properties:

ambiguous

pKa:

ca. 7.62

Temp.:

23 °C

Remarks on result:

other: related to back protonation of amino groups

Conclusions:

The value of pKa (- log Ka) of the test substance Acid Black 210 is 7.62 at the temperature of 23 °C. This value can probably be assigned to protonation of amino groups. Sulpho groups –SO3X are in form of potassium salts and were not protonated back during the titration; thus cannot affect the pKa value.

The solution of Acid Black 210 was also titrated with NaOH solution, however no equivalence had been observed.

Executive summary:

The determination of the pKa of Acid Black 210 was conducted following OECD 112, titration method. The determined pKa = 7.62 at 23°C is due to protonation of the amino groups present in the molecule. The molecule being in the salt form is already fully dissociated.

Description of key information

7.62

Key value for chemical safety assessment

pKa at 20°C:

7.62

Additional information

A study (Michal Bartos, 2011) was performed by titration method on Acid Black 210 . The pKa of the sulfonic groups was not determined being the tested substance already in the salt form. The experimental value obtained is due to the protonation of the amino groups of the molecule. The data is therefore irrilevant