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Dissociation constant

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Reference
Endpoint:
dissociation constant
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is hydrolytically unstable (half-life less than 12 hours)

Description of key information

Dissociation constant [amino groups of constituents of amino functional alkoxysilanes]: 7.8 - 10.2

Dissociation constant [silanol groups of hydrolysis product]: pKa approximately 10

Dissociation constant [amino groups of hydrolysis product]: 9.7 – 10.9

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 constituents of the substance are expected to hydrolyse to their corresponding silanol hydrolysis product. The typical dissociation constants for the hydroxyl protons of silanetriols are available from studies in other silanetriols (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.

The dissociation constant of the amino groups of the constituents of the substance have been calculated using an appropriate predictive method to be between 7.8 - 10.2. Similarly, the amino groups of the silanol hydrolysis products have predicted dissociation constant of 9.7 - 10.9.

Reference:

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