Tetrasodium [2-({4-fluoro-6-[(2-{[4-fluoro-6-({5-(hydroxykappaO)-6-[(2-{[2-(hydroxy-kappaO)-5-sulfophenyl] diazenyl-kappaN1}-4,5-dimethoxyphenyl) diazenyl-kappaN2]-7-sulfo-2-naphthyl} amino)-1,3,5-triazin-2-yl] amino} propyl) amino]-1,3,5-triazin-2-yl} amino) benzene-1,4- disulfonato(6-)] cuprate(4-)

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

calculation (if not (Q)SAR)

Adequacy of study:

key study

Study period:

Study completion date - 02 May 2006

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

accepted calculation method

Qualifier:

no guideline required

Principles of method if other than guideline:

estimated by calculation

GLP compliance:

no

Specific details on test material used for the study:

Identity: FAT 40825/A
Batch number: CHU 297 / BOP 04/05
Purity: Organic part (Na-salt): approx. 83.7 %; All coloured components: approx. 80.54 %; Main component: approx. 59.1 %.
Appearance: Solid, black powder
Storage conditions: At room temperature at about 20 °C
Expiration date: December 31, 2010

Dissociating properties:

yes

No.:

#1

pKa:

-6.7

Remarks on result:

other: arenesulfonic acid groups (ArSO3H)

No.:

#2

pKa:

10

Remarks on result:

other: naphthol functional group

No.:

#3

pKa:

10

Remarks on result:

other: phenol

No.:

#4

pKa:

> 1.65 - < 1.85

Remarks on result:

other: The pKa values of the fluorotriazines will be comparable to the chlorotriazines (pKa approximatively between 1.65 and 1.85, but will probably be slightly higher due to the less electronegative properties of the fluorine.

Arenesulfonic acids:

FAT 40825/A contains four arenesulfonic acid groups (ArSO3H), which are known to be very strong acids. The pKa value according to the Hammett equation, independent of the substituents, is about pKa = -6.7. This low pKa is outside of the measurable range of about pKa = 0 to 14. In aqueous solutions, these functional groups will be completely dissociated.

 

Naphthol:

The pKa of a naphthol is comparable to that one of a phenol which is about pKa = 10. The most important effect is the proton donating effect of the ortho diazo functional group, which rather increases the pKa value of the test item. However, this effect is compensated by the meta sulfonic acid functional group. Therefore, the pKa of the naphthol functional group will be about pKa = 10. However, this is of no relevance because it has to be considered, that the naphthol in FAT 40825/A builds a complex with copper (Cu) together with a phenol functional group. The copper complex with these two functional groups in the molecule will be neutral over the environmentally relevant pH-range.

 

Phenol:

A phenol has a pKa of about pKa = 10. However, the para sulfonic acid group has an acid strengthening effect ( σ = 0.39 for phenols). The ortho σ value for a diazo group is not known, but is comparable to a N-alkyl substituent (e.g., σ = -0.36 for -N(CH3)2). The overall effect is almost zero and the pKa of the phenol will approximatively be pKa = 10. However, this is of no relevance because it has to be considered, that the phenol in FAT 40825/A builds a complex with copper (Cu) together with a naphthol functional group. The copper complex with these two functional groups in the molecule will be neutral over the environmentally relevant pH-range.

 

Diamino substituted fluorotriazine:

It is known that amino substituted triazines will be protonated at the ring nitrogens. The two secondary amines are therefore of no relevance. The pKa values of diamino substituted triazines are well known from the triazine herbicides. The pKa values of the fluorotriazines will be comparable to the chlorotriazines (pKa approximatively between 1.65 and 1.85), but will probably be slightly higher due to the less electronegative properties of the fluorine. In the environmental relevant pH range, this functional group of FAT 40825/A will be in its neutral form.

Conclusions:

The overall behaviour of FAT 40825/A in aqueous solutions will be dominated by the strongly acidic arenesulfonic acid groups (ArSO3H). Therefore, the molecule will be negatively charged and is present in its anionic form over the whole environmentally relevant pH range from approximatively pH 4 to 9.

Executive summary:

The purpose of this study was to estimate the dissociation constants (pKa-values) of FAT 40825/A. The molecular structure of FAT 40825/A was used for the estimation of the dissociation behaviour. The compound has several sites, which can be dissociated (acids) and one site, which can be protonated (base). The estimations are mainly based on the Hammett and Taft equations.

The overall behaviour of FAT 40825/A in aqueous solutions will be dominated by the strongly acidic arenesulfonic acid groups (ArSO3H, pKa value of -6.7). Therefore, the molecule will be negatively charged and is present in its anionic form over the whole environmentally relevant pH range from approximatively pH 4 to 9.

Description of key information

The overall behaviour of FAT 40825/A in aqueous solutions will be dominated by the strongly acidic arenesulfonic acid groups (ArSO3H, pKa -6.7). Therefore, the molecule will be negatively charged and is present in its anionic form over the whole environmentally relevant pH range.

Key value for chemical safety assessment

pKa at 20°C:

-6.7

Additional information

The purpose of this study was to estimate the dissociation constants (pKa-values) of FAT 40825/A. The molecular structure of FAT 40825/A was used for the estimation of the dissociation behaviour. The compound has several sites, which can be dissociated (acids) and one site, which can be protonated (base). The estimations are mainly based on the Hammett and Taft equations. The overall behaviour of FAT 40825/A in aqueous solutions will be dominated by the strongly acidic arenesulfonic acid groups (ArSO3H, pKa -6.7). Therefore, the molecule will be negatively charged and is present in its anionic form over the whole environmentally relevant pH range from approximately pH 4 to 9.