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Physical & Chemical properties

Water solubility

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Description of key information

Water Solubility (dimethoxy(methyl)vinylsilane): 3000 mg/l (QSAR)
Water Solubility (methylvinylsilanediol): 5.0E+05 mg/l at 20°C (QSAR)
Water solubility (methanol) = Miscible at 20°C (measured)

Key value for chemical safety assessment

Water solubility:
3 000 mg/L
at the temperature of:
20 °C

Additional information

The requirement to test the registration substance for water solubility is waived on the basis that it hydrolyses rapidly to methylvinylsilanediol and methanol. The half-lives are <<2 min at pH 4, 18.3 min at pH 7 and 0.7 min at pH 9 and 25°C.

The water solubility of the parent substance (dimethoxy(methyl)vinylsilane) has been calculated using a validated QSAR method to be 3000 mg/l at 20°C.

The silanol hydrolysis product, methylvinylsilanediol, may undergo condensation reactions in solution to give siloxane dimers, and linear and cyclic oligomers. A dynamic equilibrium is established .The overall rate and extent of condensation is dependent on nominal loading, temperature, and pH of the system, as well as what else is present in the solution.

The condensation reactions of silanediols may be modelled as an equilibrium between monomer, dimer, trimer and tetramer, with the linear tetramer cyclising to the thermodynamically stable cyclic tetramer. The reactions are reversible unless the cyclic tetramer concentration exceeds its solubility; in this case, the cyclic tetramer forms a separate phase, driving the equilibrium towards the tetramer. For methylvinylsilanediol, a solution at 100 mg/l (often the top loading used in ecotox tests) is predicted to contain >99% monomer, with small amounts of dimer, trimer, and cyclic tetramer. At loadings above about 700 mg/l the concentration of the cyclic tetramer of the silanol hydrolysis product is predicted to exceed its solubility, resulting in formation of a separate phase. In addition, the cyclic tetramer is expected to have a high volatility from water and this may cause losses from water under some conditions. Further information is given in a supporting report (PFA 2013am) attached in Section 13 of the IUCLID dataset.

The initial hydrolysis product, methylvinylsilanediol, is very hydrophilic and hence the calculated solubility is 5E+05 mg/l using a QSAR method. However, the saturation concentration of methylvinylsilanediol in water is limited by condensation reactions rather than lack of true solubility, as discussed above. The prediction is however considered valid for use in calculation of the Henry’s Law Constant and for environmental exposure modelling because it is considered to adequately describe the hydrophilicity of the substance and hence the partitioning behaviour.

Methanol is miscible in water at 20°C, based on experimental data (OECD 2004).

References:

PFA, 2014am, Peter Fisk Associates, Silanols and aquatic systems, 350.001.003

OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1.