Registration Dossier

Data platform availability banner - registered substances factsheets

Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Physical & Chemical properties

Water solubility

Currently viewing:

Administrative data

Link to relevant study record(s)

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)

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).



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