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Physical & Chemical properties

Water solubility

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Description of key information

Water solubility [(trimethoxysilylpropyl)methylmethylphosphonate]: 1.0E+06 mg/L at 20°C (QSAR)

Water solubility [bis(trimethoxysilylpropyl)methylphosphonate]: 4.3E+04 mg/L (QSAR)

Water solubility [(trihydroxysilylpropyl)methylmethylphosphonate]: Above approximately 1000 mg/L condensation reactions can occur over time, limiting the concentration dissolved in water. The calculated water solubility is 1.0E+06 mg/L (QSAR)

Water solubility [bis(trihydroxysilylpropyl)methylphosphonate]: Above approximately 100 -500 mg/L condensation reactions can occur over time, limiting the concentration dissolved in water. The calculated water 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 submission substance is waived on the basis that the constituents of the substance hydrolyse rapidly to form their corresponding silanol hydrolysis products and methanol.

The water solubilities of the constituents have been predicted using a validated QSAR estimation method. The predicted water solubilities are 1.0E+06 mg/L at 20°C and 4.3E+04 mg/L at 20°C for Constituent 1 and Constituent 2 respectively.

In contact with water, the constituents hydrolyse rapidly to form (trihydroxysilylpropyl)methylmethylphosphonate (HP 1) and bis(trihydroxysilylpropyl)methylphosphonate (HP 2) as the silanol hydrolysis products for Constituent 1 and Constituent 2 respectively. The other hydrolysis product is methanol for both constituents.

The silanol hydrolysis products, may undergo condensation reactions in solution to give siloxane dimers, and linear and cyclic oligomers; at higher loadings, cross-linking reactions may occur.  The reactions are reversible unless the concentration of oligomers exceeds their solubility; in this case, the oligomers form a separate phase, driving the equilibrium towards the oligomers. 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.

 

For silanetriols, 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. There is little available information about the concentration at which bis[silanetriol] compounds such as the silanol hydrolysis product of Constituent 2 will start to undergo significant condensation; it is most likely to be in the range of 100-500 mg/L. Further information is given in a supporting report (PFA 2016am) attached in Section 13.

Methanol is reported as miscible in water at 20°C (OECD 2004).

 

References:

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