Registration Dossier
Registration Dossier
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EC number: 213-668-5 | CAS number: 999-97-3
Dissociation constant
Administrative data
Link to relevant study record(s)
- 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)
Reference
Description of key information
Dissociation constant [1,1,1,3,3,3-hexamethyldisilazane]: not relevant due to very rapid hydrolysis in contact with water
Dissociation constant [trimethylsilanol]: pKa approximately 11
Dissociation constant [ammonium ion]: 9.25
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 to form trimethylsilanol and ammonia.
Silanols are not expected to undergo significant dissociation within an environmental relevant range. This is supported by measured data for trimethylsilanol which is reported in a secondary literature to have a first dissociation constant pKa of approximately 11. Additional information is given in a supporting report (PFA 2013b) attached in Section 13.
The pKa of the ammonium ion, NH4+, is given in a reliable handbook as 9.25 (Haynes W. M, Lide D.R. (ed.) 2010).
References:
Haynes W. M, Lide D.R. (ed.) 2010. CRC Handbook of Chemistry and Physics. 91st Edition. Boca Raton: CRC Press
PFA (2013b). Peter Fisk Associates, Dissociation constant Analogue report, PFA.300.001.001
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