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Physical & Chemical properties

Partition coefficient

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partition coefficient
Data waiving:
study technically not feasible
Justification for data waiving:
the study does not need to be conducted because the substance decomposes
partition coefficient
Type of information:
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Justification for type of information:
See attached QMRF/QPRF
Principles of method if other than guideline:
The result was obtained using an appropriate QSAR method (see attached QMRF and QPRF for details).

The model is an adaptation of the existing SRC model KOWWIN v1.67, which is a component of the EPIWIN Suite. The model is based on fragment values. That is, the chemical structure is broken down into its constituent functional groups, and the contribution of each group toward the overall partition coefficient is calculated. The constants used within KOWWIN have been derived by SRC from a wide range of organic chemicals. Whilst this method is good in principle, the model was developed using a wide range of organic chemicals and only a few organosilicon compounds. Therefore, a validation procedure was undertaken to assess the applicability of the model to alkoxysilane compounds. It was noted that the model under-predicted log Kow for alkoxysilanes; therefore, a correction factor is applied when this structural feature is present. The adapted model applies to di- and tri-alkoxysilanes.
Partition coefficient type:
Key result
log Pow
Partition coefficient:
20 °C
ca. 7
A log Kow value of 0.2 at 20°C was obtained for the substance using an accepted calculation method. The result is considered to be reliable.

Description of key information

Log Kow [trimethoxysilane]: Not relevant due to very rapid hydrolysis in contact with water

Log Kow [methanol]: -0.82 to -0.64

Key value for chemical safety assessment

Additional information

The requirement to conduct a n-octanol/water partition coefficient study for the submission substance is waived because in contact with water, the substance hydrolyses very rapidly.

However, the log Kow of trimethoxysilane has been predicted to be 0.2 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.

log Kow is not relevant for inorganic compounds such as silanetriol and silicic acid, nor is it relevant for hydrogen gas.

The purpose of the log Kow study is to understand the interaction of the substance with water and octanol, which acts as a model for lipids in humans and organisms and for organic carbon in soils and sediments. On the basis of structure and supported by predictions, monosilicic acid and silanetriol have a high affinity with water and low affinity for lipids and organic carbon.

Methanol has a reported log Kow value of -0.82 to -0.64 (OECD 2004).


OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1.