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Dissociation constant

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Description of key information

[3-(triethoxysilyl)propyl]urea (amine groups): First pKa = 1.0
[3-(trihydroxysilyl)propyl]urea (hydroxy groups): pKa = approximately 10, based on read-across from phenylsilanetriol

Key value for chemical safety assessment

Additional information

For the amine groups of the substance a first pKa value of 1.0 was obtained using an appropriate calculation method. This suggests that no ionisation is expected in an environmentally relevant range.

In contact with water the substance will hydrolyse to form 3-(trihydroxysilyl)propyl]urea and ethanol. 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)propyl]urea from phenylsilanetriol. This suggests that the hydroxy groups 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 of approximately 10 in a reliable study using a relevant test method, (reliability 1; read-across conclusion is given reliability 2). Additional information is given in a supporting report (PFA 2013b) attached in Section 13 of the REACH technical dossier.

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