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Physical & Chemical properties

Dissociation constant

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Description of key information

Dissociation constant [3-[tris(acetoxy)silyl]propyl methacrylate]: Not relevant

Dissociation constant [3-(trihydroxysilyl)propyl methacrylate]: pKa approximately 10 (read-across)

Dissociation constant [acetic acid]: pKa 4.74

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 are 3-(trihydroxysilyl)propyl methacrylate and acetic acid.

There are no reliable measured data for the dissociation constant of 3-(trihydroxysilyl)propyl methacrylate. 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 methacrylate 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. Additional information is given in a supporting report (PFA 2013b) attached in Section 13.

A pKa of 4.74 was reported for acetic acid in a handbook of data which has been subject to peer-review and in which the original data sources are traceable (O'Neil MJ, 2013). The result is considered to be reliable.


O’Neil MJ (2013). O’Neil MJ (Editor-in-Chief). The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals, Fifteenth Edition, The Royal Society of Chemistry, UK, 2013.

PFA (2013b). Peter Fisk Associates, Dissociation constant Analogue report, PFA.300.001.001.