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Physical & Chemical properties

Dissociation constant

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Description of key information

Dissociation constant [substance]: Not relevant due to very rapid hydrolysis in contact with water

Dissociation constant [silanol hydrolysis product]: pKa approximately 11

Dissociation constant [acrylic acid]: pKa 4.25 at 25°C

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 very rapidly. The hydrolysis products in this case are tris(1-methylethyl)silanol and acrylic acid. There are no reliable measured data for the dissociation constant of tris(1-methylethyl)silanol. The typical dissociation constants for the hydroxyl protons of silanols are available from studies in other silanols. It is appropriate to read-across dissociation constant data for tris(1-methylethyl)silanol from trimethylsilanol. This suggests that silanols are not expected to undergo significant dissociation within the range of pH relevant in the environment or in vivo. Trimethylsilanol is reported in a secondary source to have a dissociation constant of approximately 11.

Acrylic acid has a reported dissociation constant of 4.25 at 25°C (CRC 2010).


CRC (2010) CRC Handbook of Chemistry and Physics: A Ready-Reference Book of Chemical and Physical Data, 91st edition, CRC Press, Boca Raton, 2010