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Dissociation constant

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dissociation constant
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is hydrolytically unstable (half-life less than 12 hours)

Description of key information

Dissociation constant (di-amine group): pKa1 = 7.2, pKa2 = ca. 10 (Estimation)


Dissociation constant [N-(3-(trihydroxysilyl)propyl)ethylenediamine, silanetriol group]: ca. 10

Key value for chemical safety assessment

Additional information

The requirement to conduct a dissociation constant study for the submission substance is waived because in contact with water the substance hydrolyses very rapidly. The hydrolysis products in this case are N-[3-(trihydroxysilyl)propyl]ethylenediamine and methanol.


There are no reliable measured data for the dissociation constant of N-[3-(trihydroxysilyl)propyl]ethylenediamine. The typical dissociation constants for the hydroxyl protons of silanetriols are available from studies in other silanetriols. It is appropriate to read-across dissociation constant data for the silanol hydrolysis product; N-[3-(trihydroxysilyl)propyl]ethylenediamine from phenylsilanetriol. This suggests that silanols are not expected to undergo significant dissociation within the range of pH relevant in the environment or in vivo. Phenylsilanetriol has a measured first dissociation constant ca.10 in a reliable study using a relevant test method. Additional information is given in a supporting report (PFA 2013b) attached in Section 13.


The dissociation constant of the two amine groups have been calculated using an appropriate predictive method to be pKa1 = 7.2 and pKa2 = ca. 10. Based on the different pKa values for the two different amine groups present in the diamine, at environmentally relevant pH range the diamine group will exist in a mixture of singly and doubly protonated species.