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Physical & Chemical properties

Dissociation constant

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Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Principles of method if other than guideline:
Titration method (no further details available)
GLP compliance:
not specified
Dissociating properties:
yes
No.:
#1
pKa:
11.9
Remarks on result:
other: no data on temperature or pH was provided
Conclusions:
A dissociation constant of 11.9 is reported in secondary literature for a silanediol, which is a structural analogue to the hydrolysis product of the submission substance. The original reference was not available for review and no further information is available. The reliability of this result is not assignable.
Endpoint:
dissociation constant
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Please refer to additional information field in the endpoint study summary (Dissociation constant).
Reason / purpose:
read-across source
Dissociating properties:
yes
No.:
#1
pKa:
11.9
Remarks on result:
other: Temperature and pH not provided.
Conclusions:
A dissociation constant of 11.9 is reported in secondary literature for a silanediol, which is a structural analogue to the hydrolysis product of the submission substance. The original reference was not available for review and no further information is available. The reliability of this result is not assignable.

Description of key information

Dissociation constant (substance): Not relevant
Dissociation constant (silanol hydrolysis product): approximately 10-12, based on read-across from phenylsilanetriol and dimethylsilanediol.

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 rapidly hydrolyses to form diphenylsilanediol and hydrochloric acid.

There are no reliable measured data for the dissociation constant of diphenylsilanediol. The typical dissociation constants for the hydroxyl protons of silanediols are available from other silanediols. It is appropriate to read-across dissociation constant data for diphenylsilanediol from dimethylsilanediol. Dimethylsilanediol has a measured first dissociation constant of approximately 11.9 reported in secondary literature.

It is also appropriate to read-across dissociation constant data from phenylsilanetriol to diphenylsilanediol. Phenylsilanetriol has a measured first dissociation constant of approximately 10 reported in a reliable study using a relevant test method, (reliability 1; read-across conclusion is given reliability 2).

The two studies suggest that silanols are not expected to undergo significant dissociation within the range of pH relevant in the environment or in vivo. Additional information is given in a supporting report (PFA, 2013b) attached in Section 13 of the REACH technical dossier.