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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)

Description of key information

Water solubility [Constituent 1; N-[3-(trimethoxysilyl)propyl]-1,3-benzenedimethanamine]: 4.1E+04 mg/L at 20°C (QSAR)

Water solubility [Constituent 2; -[(2,2-dimethoxy-1,2-azasilolidin-1-yl)benzenedimethanamine]: not relevant, very rapid hydrolysis

Water solubility [N-[3-(trihydroxysilyl)propyl]-1,3-benzenedimethanamine]: Above approximately 1000 mg/L condensation reactions can occur over time, limiting the concentration dissolved in water. The calculated solubility is 1.0E+06 mg/L (QSAR).

Water Solubility [methanol]: miscible 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 the constituents hydrolyse either rapidly or very rapidly in contact with water. The final hydrolysis products in this care are N-[3-(trihydroxysilyl)propyl]-1,3-benzenedimethanamine and methanol.

Measurement of the water solubility of the registration substance was attempted in accordance with EU Method A.6. However, due to the rapid/very rapid hydrolysis of the constituents of the substance, only a preliminary study was performed. About 0.1 - 0.5 mg of the test substance was added to 100 mL double-distilled water, the solution was equilibrated at 20±0.5°C and the resulting solution was visually observed immediately after addition of the double-distilled water. A water solubility value of 1.23 - 1.42 g/L at 20±0.5°C and pH 10.2 -10.3 was determined by visual inspection. Due to the rapid/very rapid hydrolysis of the constituents of the test substance, it is possible that equilibrium was not attained and the products of hydrolysis might have influenced the results observed.

The water solubility of Constituent 1, N-[3-(trimethoxysilyl)propyl]-1,3-benzenedimethanamine has been calculated using a validated QSAR method to be 4.1E+04 mg/L at 20°C. For Constituent 2, water solubility is not predicted due to its very rapid hydrolysis in contact with water.

The silanol hydrolysis product, N-[3-(trihydroxysilyl)propyl]-1,3-benzenedimethanamine, 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. At higher loadings, cross-linking reactions may occur. At loadings below 500 mg/L of N-[3-(trihydroxysilyl)propyl]-1,3-benzenedimethanamine, 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 ultimate hydrolysis product, N-[3-(trihydroxysilyl)propyl]-1,3-benzenedimethanamine, 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.

Methanol is miscible with water at 20°C (OECD 2004).



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


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