Reaction mass of pentasodium 2-{[4-chloro-6-(ethyl{3-[(2-sulfonatoethyl)sulfonyl]phenyl}amino)-1,3,5-triazin-2-yl]amino}-5-hydroxy-6-({2-sulfonato-4-[(4-sulfonatophenyl)diazenyl]phenyl}diazenyl)naphthalene-1,7-disulfonate and tetrasodium 2-[(4-chloro-6-{ethyl[3-(vinylsulfonyl)phenyl]amino}-1,3,5-triazin-2-yl)amino]-5-hydroxy-6-({2-sulfonato-4-[(4-sulfonatophenyl)diazenyl]phenyl}diazenyl)naphthalene-1,7-disulfonate

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

calculation (if not (Q)SAR)

Remarks:

estimated by calculation

Adequacy of study:

key study

Study period:

02 March 2006

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

accepted calculation method

Qualifier:

no guideline followed

Principles of method if other than guideline:

Estimation of dissociation constant, as the substance is a sulphonate (having an arenesulfonic acid function and an aliphatic sulphonic acid function, both known to be very strong acid functions with negative pKa values (-6.7 and -2.5 respectively). The remaining functional groups of the molecule are of minor importance. Thus, in aqueous solution such sulphnic acids are completely dissociated in the environmentally relevant pH range (4 - 9) and an experimental determination is not required.

GLP compliance:

no

Specific details on test material used for the study:

Identity: FAT 40824/A
Batch: Red ROE 805 BOP 04/05
Appearance: dark red powder
Purity: Organic part (Na-salt): approx. 82 %; Main component 1 : approx. 36.2 %; Main component 2: approx. 27.5 %; Oligomers: 10 %
Expiration date: 01 October 2010
Storage: At room temperature at about 20 °C in a desiccator (hygroscopic)

Dissociating properties:

yes

No.:

#1

pKa:

-6.7

Remarks on result:

other: Arenesulfonic acids

No.:

#2

pKa:

-2.5

Remarks on result:

other: Aliphatic sulfonic acid

No.:

#3

pKa:

10

Remarks on result:

other: Naphthyl phenole

No.:

#4

pKa:

> 1.65 - < 1.85

Remarks on result:

other: Diamino substituted chlorotriazine

The molecular structure of the main component of FAT 40824/A was used for the estimation of the dissociation behaviour. The structure of the main component does not differ much from the second component (only one sulfonic acid functional group more) and has therefore no influence of the general acid/base 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 Hammet and Taft equations given in Reference (1).

Arenesulfonlc acids

FAT 40824/A contains three arenesulfonic acid groups (ArSO3H), which are known to be very strong acids. The basic pKa value, independent of the substituents, is about at pKa = -6.7. This low pKa is outside of the measurable range of about pKa = O to 14. In aqueous solutions, these functional groups will be completely dissociated.

 

Aliphatic sulfonlc acid

The main component of FAT 40824/A contains one aliphatic sulfonic acid as sulfonate (R­ OSO3H). Also these acid is very strong with a pKa value of about - 2.5, which is outside of the measurable range. In aqueous solutions, this functional group will be completely dissociated.

 

Naphthyl phenole

The pKa of a napthyl phenole is comparable to that one of a phenole which is about pK. = 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. Therefore, this functional group will be protonated over the whole relevant environmental range (no dissociation).

 

Diamino substituted chlorotriazine

It is known that amino substituted triazines will be protonated at the ring nitrogens. The secondary amines are therefore of no relevance. The pKa values of diamino substituted chlorotriazines are well known from the triazine herbicides (pKa approximatively between 1.65 and 1.85 (Reference 8). In the environmental relevant pH range, this functional group of FAT 40824/A will be in its neutral form.

Conclusions:

The overall behaviour of FAT 40824/A in aqueous solutions will be dominated by the strongly acidic sulfonic acid groups (R-SO3H). Therefore, the molecule will be negatively charged and is present in its anionic form over the whole environmentally relevant pH range from approximatively 4 to 9.

Executive summary:

The molecular structure of the main component of FAT 40824/A was used for the estimation of the dissociation behaviour. The structure of the main component does not differ much from the second component (only one sulfonic acid functional group more) and has therefore no influence of the general acid/base behaviour. The overall behaviour of FAT 40824/A in aqueous solutions will be dominated by the strongly acidic sulfonic acid groups (R-SO3H). Therefore, the molecule will be negatively charged and is present in its anionic form over the whole environmentally relevant pH range from approximatively 4 to 9.

Description of key information

The overall behaviour of FAT 40824/A in aqueous solutions will be dominated by the strongly acidic sulfonic acid groups (R-SO3H). Therefore, the molecule will be negatively charged and is present in its anionic form over the whole environmentally relevant pH range from approximately 4 to 9.

Key value for chemical safety assessment

pKa at 20°C:

-6.7

Additional information

The molecular structure of the main component of FAT 40824/A was used for the estimation of the dissociation behaviour. The structure of the main component does not differ much from the second component (only one sulfonic acid functional group more) and has therefore no influence of the general acid/base behaviour. The overall behaviour of FAT 40824/A in aqueous solutions will be dominated by the strongly acidic sulfonic acid groups (R-SO3H). Therefore, the molecule will be negatively charged and is present in its anionic form over the whole environmentally relevant pH range from approximately 4 to 9.