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Physical & Chemical properties

Water solubility

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Description of key information

Water solubility [4,4,13,13-tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane]: ≤1 mg/l (OECD 105)

Water solubility [(3-{[3-(trihydroxysilyl)propyl]disulfanyl}propyl)silanetriol]: the concentration dissolved in water is limited to about 1000 mg/l by condensation reactions, predicted water solubility is 1.0E+06 mg/L

Water Solubility [ethanol]: miscible at 20°C

Key value for chemical safety assessment

Water solubility:
1 mg/L
at the temperature of:
25 °C

Additional information

A measured water solubility of approximately 1 mg/l was determined for the substance in a study similar to the preliminary test described in OECD Guideline 105. The study is limited by the shortened time-scale and the fact that only the preliminary test was carried out. Further testing was not carried out because the substance was suspected to be hydrolytically unstable but the half-life was not known. The study gives an indicative value of the solubility of the substance. A predicted water solubility value of 0.014 mg/l at 20°C was determined for the substance using a validated QSAR estimation method. The two reliable results are therefore used as weight of evidence.

In a secondary source to which reliability could not be assigned, water solubility value of <1 mg/l at 20°C was reported for the substance.

In contact with water, the substance hydrolyses at a moderate rate to form (3-{[3-(trihydroxysilyl)propyl]disulfanyl}propyl)silanetriol and ethanol. The silanol hydrolysis product, (3-{[3-(trihydroxysilyl)propyl]disulfanyl}propyl)silanetriol, may undergo condensation reactions in solution to give siloxane dimers, linear and cyclic oligomers and highly cross-linked polymeric particles (sol) that may overtime form an insoluble gel and 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 solution.

The condensation reactions of silanetriols may be modelled as an equilibrium between monomer, dimer, trimer and tetramer, with the linear tetramer cyclising to the thermodynamically stable cyclic tetramer. At higher loadings, cross-linking reactions may occur. The reactions are reversible unless the cyclic tetramer concentration exceeds its solubility; in this case, the cyclic tetramer forms a separate phase, driving equilibrium towards the tetramer. At loadings below 500 mg/l of (3-{[3-(trihydroxysilyl)propyl]disulfanyl}propyl)silanetriol, the soluble monomer is expected to predominate in solution (>99%), with small amounts of dimer and oligomers. Condensation reactions are expected to become important at loadings above about 1000 mg/l causing the formation of insoluble polymeric particles (sols) and gels over time. Further information is given a supporting report (PFA 2016am) attached in Section 13.

The hydrolysis product, (3-{[3-(trihydroxysilyl)propyl]disulfanyl}propyl)silanetriol, is very hydrophilic and hence the calculated solubility is 1.0E+06 mg/l 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 reaction 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.

Ethanol is miscible with water (Riddick et al 1986).

References:

PFA (2016am). Peter Fisk Associates, Silanols and aquatic systems, 404.105.003.

Riddick JA (1986). Riddick, J.A.; Bunger, W.B.; Sakano, T.K.; Organic Solvents: Physical Properties and Methods of Purification. Techniques of Chemistry. 4th ed: Wiley-Interscience. 2:pp.1325 1986