Tetrasodium 5-[4-chloro-6-(N-ethyl-anilino)-1,3,5-triazin-2-ylamino]-4-hydroxy-3-(1,5-disulfonatonaphthalen-2-ylazo)-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:

12.10.1993 to 25.10.1993

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

other: "Anmeldung neuer Farbstoffe: Richtlinie für die Begründung des Weglassens gewisser Minimalangaben" of February, 1990 (Ref. We/281)

Principles of method if other than guideline:

The spectrophotometric titration method according to Albert and Serjeant was used (Albert, A and Serjeant, E.P.: Ionization Constants of Acids and Bases, Wiley Inc. New York 1962 and Albert, A. and Serjeant, E.P., The determination of Ionization Constants, Chapman and Hall Ltd., 1971).

GLP compliance:

yes

Specific details on test material used for the study:

- Name: FAT 40406/A
- Purity: 89.3 %
- Source and lot/batch No. of test material:
SR 6947/14

Dissociating properties:

yes

No.:

#1

pKa:

> -3 - < -2.5

Remarks on result:

other: SO3-, acidic (4x)

No.:

#2

pKa:

ca. 0.8

Remarks on result:

other: Ph-NH-Tr, basic (1x)

No.:

#3

pKa:

ca. 0.8

Remarks on result:

other: Ph-N(Et)-Tr, basic (1x)

No.:

#4

pKa:

> 11

Remarks on result:

other: OH in alpha-Naphthol, acidic (1x)

The test compound had the following dissociable functional groups:

1. Four acidic aromatic –SO3 group in substituted naphthol rings.

2. One very weakly basic diphenylamine type secondary amines between a triazine and a naphthol ring.

3. One very weakly basic diphenylamine type tertiary amine between a phenyl ring and a triazine ring.

4. One weakly acidic OH group in substituted naphthol rings type alpha-naphthol

Conclusions:

FAT 40406/A has dissociating properties, because the molecule will be fourfold negatively charged over the whole environmentally relevant pH region.

Executive summary:

In a GLP-compliant study, the dissociation constant in water of the test substance was determined and four pKa's were estimated. The important pKa's are from the strongly acidic -SO3 groups. Therefore, the molecule is negatively charged over the whole environmentally relevant pH range. The possible protonation of the weakly basic amino groups and ionisation of the weakly acidic OH group will only have a very small effect in the unimportant, pH regions below 3 and above 11.

Description of key information

Reactive Red 245 has dissociating properties, because the molecule will be fourfold negatively charged over the whole environmentally relevant pH region.

Additional information

In a GLP-compliant study, the dissociation constant in water of the test substance was determined and four pKa's were estimated (Ciba-Geigy 1993). The important pKa's are from the strongly acidic -SO₃ groups. Therefore, the molecule is negatively charged over the whole environmentally relevant pH range. The possible protonation of the weakly basic amino groups and ionisation of the weakly acidic OH group will only have a very small effect in the unimportant, pH regions below 3 and above 11.