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Physical & Chemical properties

Water solubility

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Description of key information

Water solubility [Triethoxy(2,4,4-trimethylpentyl)silane]: <0.1 mg/l at 20°C

Water solubility [(2,4,4-trimethylpentyl)silanetriol]: the concentration dissolved in water is limited to about 200 mg/l by condensation reactions, calculated solubility is 2.4E+05 mg/L

Water solubility [ethanol]: miscible at 20°C

Key value for chemical safety assessment

Additional information

Two reliable water solubility values are available for the substance. A water solubility value of <0.1 mg/l at 20°C was determined for the substance using a relevant test method and in compliance with GLP. The result is considered to be reliable and selected as key study. In the second reliable study, a water solubility value of <0.25 mg/l at room temperature was determined for the substance. The key study was selected to be the one that used the more sensitive analytical method. This value is in agreement with the key study that the substance is insoluble in water and is thus used as a supporting study.

In a secondary source to which reliability could not be assigned, a water solubility value of <10 mg/l was reported for the substance.

The silanol hydrolysis product, (2,4,4-trimethylpentyl)silanetriol may undergo condensation reactions in solution to give siloxane dimers, linear and cyclic oligomers and highly cross-linked polymeric particles (sol) that may over time 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 the 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 the equilibrium towards the tetramer. For (2,4,4-trimethylpentyl)silanetriol, 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 200 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. Further information is given in a supporting report (PFA 2016am) attached in Section 13.

The hydrolysis product, (2,4,4-trimethylpentyl)silanetriol, is very hydrophilic and hence the calculated solubility is 2.4E+05 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 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 and toxicokinetic modelling because it is considered to adequately describe the hydrophilicity of the substance and hence the partitioning behaviour.

Ethanol is miscible with water (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).


PFA (2016am). Silanol and aquatic systems. Reference: 404.105.003