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Physical & Chemical properties

Water solubility

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water solubility
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is hydrolytically unstable at pH 4, 7 and 9 (half-life less than 12 hours)
water solubility
Type of information:
Adequacy of study:
supporting study
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 WaterNT v 1.01, aka WaterFrag, which is a component of the EPI Suite. This 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 solubility is calculated. Certain correction factors may also apply. Whilst this method is good in principle, it suffers from not having reliable fragment values for substances containing Si-O bonds. Therefore, multiple linear regression on a set of organosilicon compounds has been used to generate new fragment values for silicon and oxygen bound to silicon (with separate values for –OH and other oxygen). The adapted model applies to substances containing Si-O bonds.
Water solubility:
59 000 mg/L
20 °C
A water solubility of 5.9E+04 mg/l was obtained for octylsilanetriol using an appropriate calculation method.

Description of key information

Water solubility [trichloro(octyl)silane]: data waiver due to very rapid hydrolysis in contact with water

Water Solubility [octylsilanetriol]: At concentrations above 100 mg/L condensation reactions can occur over time, limiting the concentration dissolved in water. The calculated solubility is 59000 mg/L at 20°C (QSAR)

Key value for chemical safety assessment

Additional information

The requirement to conduct a water solubility study for the registered substance is waived on the basis that in contact with water, the substance hydrolyses very rapidly to form octylsilanetriol and hydrochloric acid.

The hydrolysis product, octylsilanetriol, may undergo condensation reactions in water; this become important above approximately 100 mg/L and can limit the concentration dissolved in water. For details, see the overall physicochemical properties discussion.

Octylsilanetriol is very hydrophilic and hence the calculated solubility is 5.9E+04 mg/L at 20°C using a QSAR method. This QSAR method for water solubility cannot be validated for silanetriols because the saturation concentration of silanetriols in water is limited by condensation reactions rather than lack of true solubility. The prediction is considered to be valid for use in calculation of environmental exposure modelling and toxicokinetics modelling because it is considered to adequately describe the hydrophilicity of the substance and hence the partitioning behaviour.