2,4,6-trimethyl-2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane

Partition coefficient

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

partition coefficient

Data waiving:

study technically not feasible

Justification for data waiving:

the study does not need to be conducted because the substance does not dissolve in water or in octanol

other:

Reference 2

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 the publicly available KOWWIN v1.68 program (USEPA 2011). KOWWIN is part of EPI Suite v4.1 and may be downloaded from http://www.epa.gov/oppt/exposure/pubs/episuite.htm. 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 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 http://www.epa.gov/oppt/exposure/pubs/episuite.htm

Partition coefficient type:

octanol-water

Key result

Type:

log Pow

Partition coefficient:

9

Temp.:

20 °C

pH:

ca. 7

Conclusions:

An octanol-water partition coefficient value of 9 was obtained using an accepted calculation method. The result is considered to be reliable.

Reference 3

Endpoint:

partition coefficient

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: An attempt to conduct a log Kow study for the substance using HPLC method proved unsuccessful due to the unsuitability of current method to highly fluorinated compounds.

Qualifier:

according to guideline

Guideline:

OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)

GLP compliance:

no

Type of method:

HPLC method

Partition coefficient type:

octanol-water

Analytical method:

high-performance liquid chromatography

Remarks on result:

other: Method was found not to be suitable for highly fluorinated compunds

The measured retention times and capacity factors for thiourea and the complete set of reference substances are given in Table 1. The capacity factors of the 1-alkanols and FTOHs relative to their reference values of log K_ow shows that the FTOHs have a different log k–log K_ow relationship than the 1-alkanols. Part of this discrepancy can be attributed to the larger values of A for the FTOHs. However, the resulting estimated values of log K_ow, which take into account this difference in A between the two classes, deviate from the reference values by up to 1 log unit for the FTOHs, whereas the deviations are within 0.2 log units for the 1-alkanols. These latter deviations are comparable to the standard error of the validated method.

Table 1. Measured retention times and resulting estimates of octanol-water partition coefficients for 1-alkanol and FTOH reference compounds.

Compound	Retention Time (min)	k	log Kow		Difference (Est.–Ref.)
			Est. value	Ref. value
Thiourea	0.204, 0.127^a	n.a.	n.a.	n.a.	n.a.
1-Octanol	0.397	2.51	3.23	3.07	0.16
1-Decanol	0.696	6.39	4.21	4.18	0.03
1-Dodecanol	1.465	16.4	5.20	5.13	0.07
1-Tetradecanol	3.421	41.8	6.19	6.36	-0.17
6-2 FTOH	0.549	4.48	4.15	4.70	-0.55
8-2 FTOH	1.105	11.7	5.16	6.14	-0.98

^aMean value of 3 determinations in each case, with standard deviation of±0.001. Single determinations for reference compounds.

Executive summary:

References:

1) Organization for Economic Co-operation and Development (OECD) Guideline for the Testing of Chemicals,Test No. 117: Partition Coefficient (n-octanol/water), High Performance Liquid Chromatography (HPLC) Method; adopted: 13 April 2004.

2) Abraham, M.H.; Chadha, H.S.; Whiting, G.S.; Mitchell, R.C. Hydrogen Bonding. 32. An Analysis of Water-Octanol and Water-Alkane Partitioning and the∆logPParameter of Seiler.J. Pharm. Sci.1994,83, 1085-1100.

3) Goss, K.-U.; Bronner, G.; Harner, T.; Hertel, M.; Schmidt, T.C. The Partition Behavior of Fluorotelomer Alcohols and Olefins.Environ. Sci. Technol.2006,40, 3572-3577.

4) Arp, H.P.H.; Niederer, C.; Goss, K.-U. Predicting the Partitioning Behavior of Various Highly Fluorinated Compounds.Environ. Sci. Technol.2006,40, 7298-7304.

5) Abraham, M.H. Scales of Solute Hydrogen-bonding: Their Construction and Application to Physicochemical and Biochemical Properties.Chem. Soc. Rev.1993,22, 73-83.

Description of key information

log K_ow [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):

9

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 K_ow up to 8.2 but no highly fluorinated reference compounds were used. The estimated log K_ow 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 (Dow Corning Corporation 2013b).

Therefore, a predicted log K_ow 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 K_ow values 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) respectively.