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Physical & Chemical properties

Water solubility

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Description of key information

Water solubility (2,2,4,4,6,6-hexamethylcyclotrisilazane): not relevant (hydrolyses very rapidly in water)

Water solubility (dimethylsilanediol): The predicted solubility (indicative of the hydrophilicity of the substance) is 1000000 mg/l. In reality the concentration that can be dissolved in water is limited to much lower levels (typically around 1000 mg/l) by condensation reactions.

Water solubility (ammonia): 510000 - 531000 mg/l at 20°C

Key value for chemical safety assessment

Additional information

The requirement to conduct a water solubility study for the substance is waived on the basis that it hydrolyses very rapidly in contact with water to form dimethylsilanediol and ammonia.

The hydrolysis product, dimethylsilanediol, may undergo condensation reactions in water; these become important above approximately 1000 mg/l and can limit the concentration dissolved in water. For details, see the overall physicochemical properties discussion.

Dimethylsilanediol is very hydrophilic and hence the calculated solubility is 1E+06 mg/l at 20°C using a QSAR method. However, the saturation concentration of dimethylsilanediol in water is limited by condensation reactions rather than lack of true solubility as discussed above. A prediction of 1E+06 mg/l is indicative but has no practical meaning. The prediction is however considered valid for use in environmental exposure modelling and toxicokinetics modelling because it is considered to adequately describe the hydrophilicity of the substance and hence the partitioning behaviour.

Ammonia has a measured water solubility of 510000 - 531000 mg/l at 20°C (OECD 2007).

Reference:

OECD (2007). SIDS Initial Assessment Report for SIAM 24, Paris, France, 17-20 April 2007, Ammonia Category.