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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 the publicly available KOWWIN v1.68 program (USEPA 2011). KOWWIN is part of EPI Suite v4.1 and may be downloaded from 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. The authors of this QMRF have carried out additional validation and found the method to be applicable to organosilicon compounds, excluding di- and tri-alkoxysilanes.

USEPA 2011. KOWWIN v. 1.68, US EPA. 2011. Estimation Programs Interface Suite™ for Microsoft® Windows, v 4.10. United States Environmental Protection Agency, Washington, DC, USA. Available at
Partition coefficient type:
Key result
log Pow
Partition coefficient:
20 °C
ca. 7
A log Kow value of -2.4 was obtained using an accepted calculation method. The result is considered to be reliable.

Description of key information

log Kow [methylsilanetriyl triacetate]: not relevant due to very rapid hydrolysis in contact with water

log Kow [methylsilanetriol]: -2.4 at 20°C (QSAR)

log Kow [acetic acid]: -0.17

Key value for chemical safety assessment

Additional information

The requirement to conduct an n-octanol/water partition coefficient for the registered substance is waived because in contact with water the substance hydrolyses very rapidly to form methylsilanetriol and acetic acid.

The log Kow of the silanol hydrolysis product, methylsilanetriol has been determined to be -2.4 at 20°C using a validated QSAR estimation method.

A partition coefficient value of -0.17 was reported in a secondary literature for acetic acid (Hansch et al., 1995).



Hansch et al. (1995). Hansch C, Leo A and Hoekman D. Exploring QSAR. Hydrophobic, Electronic, and Steric Constants. ACS Professional Reference Book. Washington, DC: American Chemical Society, 1995.