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Partition coefficient

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Endpoint:
partition coefficient
Type of information:
(Q)SAR
Adequacy of study:
key study
Reliability:
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:
octanol-water
Type:
log Pow
Partition coefficient:
0.2
Temp.:
20 °C
pH:
ca. 7
Conclusions:
log Kow value of 0.2 was obtained for the substance using a QSAR method. The training set contains only a limited number of alkoxysilanes and none are very close analogues of the target substance. However, a measurement of log Kow is not considered feasible due to the rapid hydrolysis of the substance. In this context, the prediction is considered sufficient to give an estimate of the log Kow of the substance.
Endpoint:
partition coefficient
Data waiving:
study technically not feasible
Justification for data waiving:
the study does not need to be conducted because the substance decomposes

Description of key information

log Kow [3-(trimethoxysilyl)propiononitrile]: Data waiver due to rapid hydrolysis in water

log Kow [3-(trihydroxysilyl)propiononitrile]: -2.9 (QSAR)

log Kow [methanol]: 0.82 to -0.64

Key value for chemical safety assessment

Additional information

The requirement to conduct an n-octanol/water partition coefficient for the substance is waived because in contact with water, the substance hydrolyses rapidly to form 3-(trihydroxysilyl)propiononitrile and methanol. The predicted hydrolysis half-lives at 20-25°C are 0.1 h at pH 4, 1.1 h at pH 7 and 0.02 h at pH 9.

However, the log Kow of the parent substance has been predicted to be 0.2 using a QSAR estimation method.

The silanol hydrolysis product also has a predicted log Kow value of -2.9 using a validated QSAR estimation method.

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

Reference:

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