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Physical & Chemical properties

Dissociation constant

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Description of key information

Dissociation constant (substance: thiol group): ca. 10
Dissociation constant (hydrolysis product): pKa approximately 10

Key value for chemical safety assessment

Additional information

In accordance with section 1 of REACH Annex XI, the study does not need to be conducted for the substance because there are no groups present in the molecule that are expected to ionize within an environmentally relevant range. However, in contact with water, 3-(triethoxysilyl)propanethiol will hydrolysed moderately to form 3-(trihydroxysilyl)propanethiol and ethanol. There are no reliable measured data for the dissociation constant of 3-(trihydroxysilyl)propanethiol. 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)propanethiol 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. The dissociation constant of the thiol group has been calculated using an appropriate predictive method to be ca. 10. Additional information is given in a supporting report (PFA 2013b) attached in Section 13 of the REACH technical dossier.