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Partition coefficient

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Reference
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:
Please refer to the attached QM(P)RF documents
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
Key result
Type:
log Pow
Partition coefficient:
5.2
Temp.:
20 °C
pH:
7
Remarks on result:
other: The predicted log Kow is for each constituent of the substance

The partition coefficient has been calculated for each constituent of the multiconstituent substance; the calculated value is 5.2 in each case.

Conclusions:
A log Kow value of 5.2 was obtained using an accepted calculation method. The result is considered to be reliable.

Description of key information

Log Kow (constituents of the substance): 5.2 (QSAR)


Log Kow (silanol hydrolysis products): -3.0 (QSAR)


Log Kow [ethanol]: -0.3

Key value for chemical safety assessment

Log Kow (Log Pow):
5.2
at the temperature of:
20 °C

Additional information

The low water solubility of the substance makes measurement of the n-octanol/water partition coefficient difficult. A predicted log Kow value of 5.2 at 20°C was determined for each constituents of the substance using a validated QSAR estimation method. The result is considered to be reliable.

The registered substance is a reaction mass of 4,4,13,13-tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane (S2) and 4,4,14,14-tetraethoxy-3,15-dioxa-8,9,10-trithia-4,14-disilaheptadecane (S3); in contact with water, both constituents of the substance react slowly to form (3-{[3-(trihydroxysilyl)propyl]disulfanyl}propyl)silanetriol and (3-{[3-(trihydroxysilyl)propyl]trisulfanyl}propyl)silanetriol and ethanol.

Log Kow of -3.0 at 20°C was determined for each silanol hydrolysis product of the constituents of the substance using validated QSAR estimation method.

Ethanol has a reported log Kow of -0.3 (Hansch C 1995. Hansch. C., A. Leo and D. Hoekman.1995. Exploring QSAR. Hydrophobic, Electronic, and Steric Constants. ACS Professional Reference Book.,: American Chemical Society).

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