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Physical & Chemical properties

Dissociation constant

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Description of key information

Calculated values:

pKa1=  ca 9.4  (of 8 basic aliphatic amines in piperidine rings)

pKa2=  <3  (of 4 basic triazine rings)

Key value for chemical safety assessment

Additional information

The test compound has the following dissociable functional group:

1. Eight basic aliphatic amines in piperidine rings substituted on four cormected l,3,5-triazine-2,4,6-N~ rings.

According to D.D. Perrin et al, pKa Prediction for Organic Acids and Bases, Chapman & Hall, 1981 we can estimate the pK value of the test compound:

Piperidine, 1-methyl pKa = 10.1

- delta pK (2x yN-R) = -0.72

pKa = 9.4 (8x basic)

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

2. Two weakly basic triazine, 2,4,6-N-R rings and two weakly basic triazine, 2,4-N-R, 6-NH-R rings.

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

1,3,5-triazine, 2,4,6-triethylamino is pKa = 5.84

In case of this complex molecule the substitution of each triazine ring with the two charged piperidine rings will shift the pKa from 5.84 for the triethylamino-triazine to lower level by three or more pH units.

A preliminary experiment has shown that the protonisation of triazine rings starts in the range of pH < pH 3. (see annex 1).

The photometric titration curve shows the typical course of overlapping pKa values (see annex 2). The calculation from this curve results in pK values in the range pKa -2.7 to pKa ~ 0.8.