[No public or meaningful name is available]

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:

experimental study

Adequacy of study:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: The study could not be performed due to hydrolysis of the test substance, as such the water solubility was determined by visual observation

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

GLP compliance:

yes (incl. QA statement)

Type of method:

flask method

Water solubility:

< 7.8 mg/L

Temp.:

30 °C

The observations relating to the sample mixtures are shown in Table 2

Table 2 - Results

Sample number	Concentration (g/L)	Observations
1	0.0078	Droplets of excess test material remained on the surface of the water
2	0.046	Droplets of excess test material remained on the surface of the water. The water was cloudy
3	0.10	Droplets of excess test material remained on the surface of the water. The water was cloudy

Discussion:

An attempt was made to develop an analytical method that is capable of recovering the test substance from water and measured the concentration. Working at a level of 1 mg/L, known quantities of the test substance were spiked into water using 0.2% v/v acetonitrile as the spiking solvent. The solution was then extracted with dichloromethane and analysed by Gas Chromatography (GC).

The resulting chromatography showed that the components in the test substance were not recovered at all, and also that components not present in standards of the test substance were present at a significant concentration in the recoveries; this suggests that, on being solvated with water, the test substance hydrolyses.

Conclusions:

A limit water solubility value of <7.8 mg/L at 30°C was obtained for the substance using a visual observation method.

Description of key information

Water solubility [Constituent 1a and Constituent 1b, cis and trans isomers]: 95 mg/L at 20°C (QSAR)

Water solubility [Constituent 2]: 2.1 mg/L at 20°C (QSAR)

Water solubility [methylsilanetriol]: 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 [2-ethylhexyl 3-[dihydroxy(methyl)silyl]propanoate]: Above approximately 10 mg/L condensation reactions can occur over time, limiting the concentration dissolved in water. The calculated solubility is 360 mg/L (QSAR)

Water solubility [methanol]: miscible at 20°C

Water solubility [2-ethylhexyl propanoate]: 24 mg/L at 20°C

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 hydrolyses either rapidly or very rapidly in contact with water.

An attempt was made to develop an analytical method that is capable of recovering the submission substance from water and measure the concentration in accordance with OECD Test Guideline 105. Working at a level of 1 mg/L, a known amount of the test substance was spiked into water using 0.2% v/v acetonitrile as the spiking solvent. The solution was extracted with dichloromethane and analysis was performed using Gas Chromatography (GC). The resulting chromatography showed that the major constituents of the substance were not recovered at all and also that constituents not present in standards of the test substance were present at a significant concentration in the recoveries. The observation is in agreement with the knowledge that the submission substance undergoes hydrolysis when in contact with water. Therefore, a limit water solubility value of <7.8 mg/L at 30°C was determined for the substance using a visual observation.

The submission substance is a multi-constituent substance; the water solubilities of the constituents were predicted to be 95 mg/L at 20°C for Constituents 1a and 1b (cis and trans isomers) and 2.1 mg/L at 20°C for Constituent 2.

The silanol hydrolysis products, methylsilanetriol and 2-ethylhexyl 3-[dihydroxy(methyl)silyl]propanoate, may undergo condensation reactions 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 silanediol/silanetriol 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 cyclic tetramer forms a separate phase, driving the equilibrium towards the tetramer. At loadings below 500 mg/L, 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 1000 mg/L for methylsilanetriol and 10 mg/L for 2-ethylhexyl-3-[dihydroxy(methyl)silyl]propanoate causing the formation of insoluble polymeric particles (sols) and gels over time.

The hydrolysis products have predicted water solubility values of 1.0E+06 mg/L for methylsilanetriol and 360 mg/L for 2-ethylhexyl- 3-[dihydroxy(methyl)silyl]propanoate 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. A prediction of 1.0E+06 mg/L is indicative but has no practical meaning but it is considered to adequately describe the hydrophilicity of the substance and hence the partitioning behaviour.

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

2-Ethylhexyl propanoate has an estimated water solubility of 24 mg/L at 20°C. The model was not validated for 2-ethylhexyl propanoate, but since there are several related substances in both the training and validation set, the estimated value is considered to be valid and reliable.

 

References:

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