Registration Dossier
Registration Dossier
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EC number: 219-637-2 | CAS number: 2487-90-3
Water solubility
Administrative data
Link to relevant study record(s)
- Endpoint:
- water solubility
- 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 at pH 4, 7 and 9 (half-life less than 12 hours)
Reference
Description of key information
Water solubility [trimethoxysilane]: Not relevant due to very rapid hydrolysis in contact with water
Water solubility [monosilicic acid and silanetriol]: approximately 100 - 150 mg SiO2/L with condensation occuring at higher concentrations.
Water solubility [methanol]: Miscible at 20°C
Key value for chemical safety assessment
Additional information
The requirement to test the substance for water solubility is waived because in contact with water the substance hydrolyses very rapidly.
However, the water solubility of trimethoxysilane has been predicted to be 1.7E+5 mg/L at 20°C using a validated QSAR estimation method.
Trimethoxysilane reacts very rapidly with water, generating silanetriol and methanol. Silanetriol reacts further to give monosilicic acid, which condenses at concentrations above approximately 100-150 mg/L as SiO2 to give insoluble amorphous polysilicic acid and hydrogen gas.
At concentrations >100-150 mg/L as SiO2 according to published sources, monomeric silanetriol/monosilicic acid condense rapidly into a highly cross-linked network (gel) or colloidal particles of polysilicic acid. The condensation rate is dependent on temperature, concentration, and acidity or alkalinity of the system. A dynamic equilibrium is established between monomer, oligomers and insoluble amorphous polysilicic acid. Further details about the chemistry of inorganic silicic acid is given in (PFA 2015ao) attached to Section 13.
Methanol is reported as miscible in water at 20°C (OECD 2004).
References:
OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1
PFA (2015ao). Peter Fisk Associates, The aquatic chemistry of inorganic silicic acid generators, PFA.404.001.001
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