6,6',6''-(1,3,5-triazine-2,4,6-triyltriimino)trihexanoic acid

Dissociation constant

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1995

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

GLP compliance:

yes

Dissociating properties:

yes

No.:

#1

pKa:

6.98

Temp.:

20 °C

Remarks on result:

other: basic groups -NH

No.:

#2

pKa:

4.5

Temp.:

25 °C

Remarks on result:

other: acidic groups -COOH

The test compound has the following dissociable functional group:

1. Three acidic aliphatic -COOH groups substituted five carbon atoms away from a triazine-2,4,6-NH- ring.

According to G. Kortiim, W. Vogel and K. Andrussow, Dissociation Constants of Organic Acids in aqueous Solution, Butterworth, London, 1961 the pK of Hexanoic acid-6-amino is 4.43 and Heptanedioic acid 4.51

For the COOH groups of the test compound we can estimate pKa = 4.5 (3x acidic)

In the pH range of these acidic pK values the test compound is extremely little soluble in water. Thus an experimental determination of these dissociation constants is not possible.

2. One weakly basic tiiazine, 2,4,6-NH-R ring.

According to D.D. Perrin, Dissociation Constants of Organic Bases in Aqueous Solution, Butterworth, London, 1965 the pK of

1,3,5-tiiazine, 2,4,6-tiiethylamino is pKa = 5.84

In case of this molecule the substitution with the three charged C5H10COO- will shift the pKa from 5.84 for the tiiethylamino-tiiazine to a higher level.

(For the experimental value, see Results.) mean value of 3 determinations

Conclusions:

The dissociation constant was determined and calculated to be pKa1= 6.98 (basic groups) and pKa2= 4.5 (acidic)

Reference 2

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2013-01-28 to 2013-03-19

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: well documented study, GLP based, in accordance to OECD guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Dissociating properties:

yes

No.:

#1

pKa:

3.886

Temp.:

20 °C

Remarks on result:

other: The pKa was in between 3.886 ± 0.016

The dissociation constant (pKa1) for the acid COOH-group was calculated for chosen 10 points of the titration curve in the well buffered region (approx. pH 3.80 to 3.88, see attached figure of titration curve of TC).

The result is the mean value of 3 replicates.

pKa2 (forthe basic NH-group) was experimentally not determinable due to instable pH-values in that test region (pH 6.7 to pH 7.5) which is illustrated in the attached figure of the titration curve of TC.

Conclusions:

The measured dissociation constant (pKa1 for the acid COOH group) of TC 65 in water at 20.0 ± 1.0°C was 3.886 ± 0.016. pKa2 (for the basic NH-group) was not determinabl in this test system.

Executive summary:

The dissociation constant(s) of 6,6’6”-(1,3,5-triazine-2,4,6-triyltriimino) tris-hexanoic acid (TC 65, commercial grade of about 65%) were determined according to the OECD guideline 112 (Dissociation constant in water) by titration of a 1.6*10-6 M solution of TC 65 with 0.05 M sodium hydroxide. The test was conducted at 20.0 ± 1.0 °C and three replicates were performed. The measured dissociation constant (pKa1 for the acid COOH group) of TC 65 was 3.886 ± 0.016. pKa2 (for the basic NH-group) was not determinable in this test system.

Description of key information

The dissociation constant(s) of 6,6’6”-(1,3,5-triazine-2,4,6-triyltriimino) tris-hexanoic acid were determined according to OECD Guideline 112.

The measured pKa1 (for the acid COOH group) was 4.5 and the pKa2 (for the basic NH-group) was 6.98.

Key value for chemical safety assessment

pKa at 20°C:

4.5