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Physical & Chemical properties

Partition coefficient

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Description of key information

Partition coefficient [2,4,6-trimethyl-2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane]: 9 at 20°C (QSAR)

Key value for chemical safety assessment

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

Additional information

The requirement to conduct an n-octanol/water partition coefficient for the substance is waived because the study is considered not technically feasible. The shake flask (OECD Test Guideline 107) and slow-stir (OECD Test Guideline 123) methods were not considered feasible due to the expected very low concentrations of the substance in the aqueous phase. The water solubility is estimated to be in the low parts per trillion range and the limit of quantification was determined to be in the low parts per billion range.

An attempt to validate an enhanced HPLC method (OECD Test Guideline 117) for the registration substance was not successful. This method has been previously validated for several methylsiloxanes having log Kow up to 8.2 but no highly fluorinated reference compounds were used. The estimated log Kow values for two highly fluorinated primary alcohols (fluorotelomer alcohols) were between 0.6 and 1 log units lower than reported known values using this method; therefore, it was concluded that the method was not appropriate for the registration substance (Kozerski 2013).

Therefore, a predicted log Kow value of 9 was determined for the parent substance using a validated QSAR estimation method. The result is considered to be reliable and used for assessment purposes.

Predicted log Kowvalues of 7.4 and 1.0 are estimated for the intermediate degradation product (

1,5-dihydroxy-1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)trisiloxane) and ultimate degradation product

( 3,3,3-trifluoropropylmethysilanediol)