Tetraethyl orthosilicate

Water solubility

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

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)

Reference 2

Endpoint:

water solubility

Type of information:

(Q)SAR

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification

Principles of method if other than guideline:

The result was obtained using an appropriate QSAR method (see attached QMRF and QPRF for details).

The model is an adaptation of the existing SRC model WaterNT v 1.01, aka WaterFrag, which is a component of the EPI Suite. This model is based on fragment values. That is, the chemical structure is broken down into its constituent functional groups, and the contribution of each group toward the overall solubility is calculated. Certain correction factors may also apply. Whilst this method is good in principle, it suffers from not having reliable fragment values for substances containing Si-O bonds. Therefore, multiple linear regression on a set of organosilicon compounds has been used to generate new fragment values for silicon and oxygen bound to silicon (with separate values for –OH and other oxygen). The adapted model applies to substances containing Si-O bonds.

Water solubility:

8 600 mg/L

Temp.:

20 °C

pH:

7

Conclusions:

A water solubility of 8600 mg/l at 20°C was obtained for the substance using an appropriate calculation method. The result is considered reliable.

Description of key information

Water solubility [tetraethyl orthosilicate]: Not relevant due to very rapid hydrolysis in contact with water

Water solubility [monosilicic acid]: Approximately 100-150 mg SiO₂/L, with condensation occurring at higher concentrations.

Water solubility [ethanol]: miscible at 20°C

Key value for chemical safety assessment

Water solubility:

8 600 mg/L

at the temperature of:

20 °C

Additional information

The requirement to conduct a water solubility study is waived because in contact with water, the submission substance hydrolyses rapidly to form monosilicic acid (CAS 10193-36-9; EC No. 233-477-0) and ethanol (CAS 64-17-5; EC No. 200-578-6).

However, the water solubility of the substance has been predicted as 8600 mg/L at 20°C using a validated QSAR estimation method. Also, a water solubility value of 1.49 g/L (1490 mg/L) at 23°C was determined for the substance based on an estimation of a saturated solution of the test substance in water (Altmann 2002). The relative amounts of water and test substance present were estimated by ¹H-NMR spectroscopy. Due to the method used, saturation of the test solution may not have been obtained. Also, an attempt was made to measure the water solubility of the submission substance based on the concentration of the substance in buffer solutions during a hydrolysis study. Water solubility in the range 258-829 µg/g (258-829 mg/L) was obtained (Dow Corning Corporation 2003). The reliability of this study is unassignable. Therefore, the predicted result is considered as a true indication of the water solubility of the submission substance and is used for assessment purposes.

Silicic acid condenses at concentrations above approximately 100-150 mg/L as SiO₂ to give insoluble amorphous polysilicic acid. At concentrations >100-150 mg/L as SiO₂ according to published sources, monomeric silicic acid condenses rapidly into a highly cross-linked network (gel) or colloidal particles of polysilicic acid. The condensation rate is dependent on temperature, concentration, and acidity or alkalinity of the system. A dynamic equilibrium is established between monomer, oligomers and insoluble amorphous polysilicic acid. Further details about the chemistry of inorganic silicic acid is given in (PFA 2015ao) attached to Section 13.

Ethanol is miscible with water (Riddick J A 1986).

References:

PFA (2015ao). Peter Fisk Associates, The aquatic chemistry of inorganic silicic acid generators, PFA.404.001.001

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