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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 [3-(trimethoxysilyl)propiononitrile]: not relevant due to rapid hydrolysis in contact with water

Dissociation constant [3-(trihydroxysilyl)propiononitrile]: pKa approximately 10

Key value for chemical safety assessment

Additional information

The requirement to test the substance for dissociation constant is waived because in contact with water the substance hydrolyses rapidly. The hydrolysis products in this case are 3-(trihydroxysilyl)propiononitrile and methanol.

There are no reliable measured data for the dissociation constant of 3-(trihydroxysilyl)propiononitrile. 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 3-(trihydroxysilyl)propiononitrile 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 had a measured first dissociation constant of approximately 10 in a reliable study using a relevant test method. Additional information is given in a supporting report (PFA 2013b) attached in Section 13.