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Physical & Chemical properties

Dissociation constant

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Description of key information

Dissociation constant (substance): No ionisable groups
Dissociation constant (hydrolysis product): pKa approximately 10

Key value for chemical safety assessment

Additional information

The requirement to test the substance for dissociation constant is waived because there are no ionisable group present in the molecule that are expected to ionize within an environmentally relevant pH range. However, in contact with water, the substance hydrolyses moderately. The hydrolysis products in this case are (3-thiocyanatopropyl)silanetriol and ethanol. There are no reliable measured data for the dissociation constant of (3-thiocyanatopropyl)silanetriol. 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-thiocyanatopropyl)silanetriol 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, (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.