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Water solubility

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Description of key information

Water solubility [2,4,6-trimethyl-2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane]: 1.3E-06 mg/l at 20°C (QSAR)

Key value for chemical safety assessment

Water solubility:
0 mg/L
at the temperature of:
20 °C

Additional information

The water solubility study for the substance, 2,4,6-trimethyl-2,4,6-tris(3,3,3-trifluoropropyl)cyclotrisiloxane (F-D3), was considered technically not feasible because of the very low solubility estimated for the substance. An attempt to conduct a water solubility study using the column elution method (OECD 105) was unsuccessful because the result of the study yielded aqueous solubilities that significantly differed outside the required variation (<30%). The tentative solubility ranged down to <0.007 mg/l. The limit of quantification of the validated analytical method was determined to be 0.005 mg/l.

A predicted water solubility of 1.3E-06 mg/l at 20°C was determined for F-D3 using a QSAR estimation method. There is some additional uncertainty associated with the result as there are no highly fluorinated compounds in the training/test set. However, the prediction is considered sufficient to indicate that the water solubility of F-D3 is very low.

In addition to information from attempts at measuring and estimating water solubility of F-D3, a measured water solubility for dodecamethylcyclohexasiloxane (D6, CAS No: 540-97-6) is available. D6 has a molecular weight of 444.9 g/mol and a measured water solubility of 0.005 mg/l (Varaprath et al 1996), and F-D3 has a slightly greater molecular weight of 468.5 g/mol. However, the structure of the latter has fewer oxygen atoms to engage in polar interactions with water that likely enhance the solubility of the former. At the same time, while both molecules contain the same number of carbon atoms, the larger and non-polar trifluoropropyl groups should act to reduce solubility relative to the methyl substitution on D6. Therefore, it is chemically reasonable that F-D3 should have water solubility that is significantly less than D6. This conclusion, based on a simple consideration of the factors that govern aqueous solubility – molecular size and capacity for polar interactions – is in quantitative agreement with estimated water solubility of F-D3.

Therefore, it is concluded that it is not technically feasible to measure the water solubility of F-D3 and the water solubility is likely to be in the parts per trillion range.

Predicted water solubility values of 4.9E-04 mg/L and 1.3E+04 mg/L 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.