2-Naphthalenesulfonic acid, 7-amino-4-hydroxy-8-[2-[2-sulfo-4-[[2-(sulfooxy)ethyl]sulfonyl]phenyl]diazenyl]-, potassium sodium salt (1:?:?), coupled with diazotized 2-[(4-amino-5-methoxy-2-methylphenyl)sulfonyl]ethyl hydrogen sulfate

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Study completion date - 20 October 2003.

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

accepted calculation method

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:

Name: FAT 40812/A

Dissociating properties:

yes

No.:

#1

pKa:

11.23

Remarks on result:

other: Hydroxy group

No.:

#2

pKa:

-0.48

Remarks on result:

other: Sulfonic acid group (2x)

No.:

#3

pKa:

-1.45

Remarks on result:

other: Primary amine

No.:

#4

pKa:

-3.9

Remarks on result:

other: Sulfuric acid ester

The hydroxy group of FAT 40812/A is protonated at pH 11.23 and below. All other sites are deprotonated above pH 0. Thus FAT 40812/A will be deprotonated at all sites but the hydroxy group all over the whole environmental relevant pH range (pH 5 to pH 8).

Conclusions:

The test substance will be deprotonated at all sites but the hydroxy group all over the whole environmental relevant pH range (pH 5 to pH 8).

Executive summary:

The dissociation constant in water of the test substance was calculated using the Hammett and Taft Correlation methods and four pKa were estimated. The hydroxy group of the test substance is protonated at pH 11.23 and below. All other sites are deprotonated above pH 0. Thus the test substance will be deprotonated at all sites but the hydroxy group all over the whole environmental relevant pH range (pH 5 to pH 8).

 

The individual pKa values are tabulated as below:

Acid/Base	pKa
Hydroxy group	11.23
Sulfonic acid group (2 x)	-0.48
Primary amine	-1.45
Sulfuric acid amine	-3.9

Description of key information

The dissociation constant in water of the test substance was calculated using the Hammett and Taft Correlation methods and four pKa were estimated (RCC 2003). The hydroxy group of the test substance is protonated at pH 11.23 and below. All other sites are deprotonated above pH 0. Thus, the test substance will be deprotonated at all sites but the hydroxy group all over the whole environmental relevant pH range (pH 5 to pH 8).