Trimethylsilane

Partition coefficient

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

partition coefficient

Type of information:

(Q)SAR

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The result was obtained by an appropriate predictive method.

Justification for type of information:

Please refer to attached justification documents

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 the publically available KOWWIN v1.68 program (USEPA 2011). KOWWIN is part of EPI Suite v4.1 and may be downloaded from http://www.epa.gov/oppt/exposure/pubs/episuite.htm. The 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 partition coefficient is calculated. The constants used within KOWWIN have been derived by SRC from a wide range of organic chemicals. The authors of this QMRF have carried out additional validation and found the method to be applicable organosilicon compounds, excluding di- and tri-alkoxysilanes.
USEPA 2011. KOWWIN v. 1.68, US EPA. 2011. Estimation Programs Interface Suite™ for Microsoft® Windows, v 4.10. United States Environmental Protection Agency, Washington, DC, USA. Available at http://www.epa.gov/oppt/exposure/pubs/episuite.htm.

Partition coefficient type:

octanol-water

Type:

log Pow

Partition coefficient:

2.2

Temp.:

20 °C

pH:

7

Conclusions:

A log Kow value of 2.2 was determined for the substance using relevant estimation method. The result is considered to be reliable.

Reference 2

Endpoint:

partition coefficient

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2008-07-01 to 2008-07-24

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: The study was conducted according to an appropriate OECD test guideline, and in compliance with GLP.

Qualifier:

according to guideline

Guideline:

OECD Guideline 107 (Partition Coefficient (n-octanol / water), Shake Flask Method)

GLP compliance:

yes (incl. QA statement)

Type of method:

shake-flask method to: flask method

Partition coefficient type:

octanol-water

Analytical method:

gas chromatography

Type:

Pow

Partition coefficient:

15.4

Temp.:

25 °C

pH:

7.1

Remarks on result:

other: mean Pow; temperature ± 0.5°C

Type:

log Pow

Partition coefficient:

1.19

Temp.:

25 °C

pH:

7.1

Remarks on result:

other: temperature ± 0.5°C

Preliminary estimate:

Approximate solubility in n-octanol: 55.2% w/w

Approximate solubility in water: 1.35% w/w

Approximate P_ow: 40.8

Log₁₀ P_ow: 1.61

Definitive test:

The mean peak areas obtained for the standard, stock and sample solutions are shown in the following two tables:

Organic phase

Solution	Mean peak area
Standard 104 mg/l	91.124
Standard 94.6 mg/l	82.157
Organic phase matrix blank	0.000
Sample 1	83.071
Sample 2	81.560
Sample 3	76.676
Sample 4	77.748
Sample 5	73.127
Sample 6	70.424
Stock solution A	87.034
Stock solution B	81.619

 

Aqueous phase

Solution	Mean peak area
Standard 5.20 mg/l	4.312
Standard 4.73 mg/l	3.845
Organic phase matrix blank	0.000
Sample 1	5.173
Sample 2	5.139
Sample 3	4.708
Sample 4	4.481
Sample 5	4.299
Sample 6	4.534

The total weights (mg) and analysed concentration (mg/l) of the respective phases are shown in the following table:

Sample Number	Volume of stock solution (ml)	Volume of n-octanol saturated water (ml)	Total Weight (mg)	Organic Phase		Aqueous Phase
				Analysed Concentration (mg/l)	Weight (mg)	Analysed Concentration (mg/l)	Weight (mg)	pH
1	50	25	48.3	952	47.6	63.0	1.58	6.8
2	50	25	48.3	935	46.7	62.6	1.57	6.8
3	40	40	38.7	879	35.2	57.3	2.29	6.9
4	40	40	38.7	891	35.7	54.6	2.18	7.0
5	25	50	24.2	838	21.0	52.4	2.62	7.0
6	25	50	24.2	807	20.2	55.2	2.76	7.0

 

pH of n-octanol saturated water: 7.1

Temperature: 25.0 ± 0.5°C

The partition coefficient determined for each sample is shown in the following table:

Sample Number	n-Octanol/Water Volume Ratio	Partition Coefficient	Log10Pow	Mean Partition Coefficient
1 2	2:1	15.1 14.9	1.18 1.17	15.0
3 4	1:1	15.3 16.3	1.19 1.21	15.8
5 6	1:2	16.0 14.6	1.20 1.17	15.3

Mean P_ow: 15.4                                Log₁₀P_ow: 1.19                                P_ow standard deviation : 0.656

Validation:

The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 0 to 10 mg/l for the aqueous phase and 0 to 150 mg/l for the stock solution and organic phase. These were satisfactory with correlation coefficients of 1.00 being obtained.

Discussion:

Substances having a log₁₀ P_ow of greater than 3 are regarded as having the potential to bioaccumulate in the environment. The test material has a predicted dissociation constant of 12.7 ± 0.6 using ACD/I-Lab Web Service (ACD/pKa 8.03). However, testing was not possible with the test material in its nonionised form as the pH would need to be approximately pH 14. Therefore, the n-octanol saturated water was adjusted to pH 7 to ensure the test material was partitioned at an environmentally relevant pH.

Conclusions:

An octanol-water partition coefficient value of 1.19 was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP. The result is considered to be reliable.

Description of key information

Partition coefficient [trimethylsilane]: 2.2 at 20°C (QSAR)
Partition coefficient [trimethylsilanol]: 1.19 at 25°C (OECD 107)
Log Kaw [trimethylsilanol]: -2.77± 0.1 at 25± 0.3°C

Key value for chemical safety assessment

Log Kow (Log Pow):

2.2

at the temperature of:

20 °C

Additional information

A log K_ow value of 2.2 at 20°C was determined for the substance using a validated QSAR estimation method. The result is considered to be reliable.

In contact with water, trimethylsilane hydrolyses slowly to form trimethylsilanol and hydrogen.

Trimethylsilanol has a measured log K_ow value of 1.19 at 25 ± 0.5°C and pH 7.1 in accordance with relevant test method and in compliance with GLP. In another disregarded study, a log K_ow of 1.62 at 40°C and pH 7 was determined for trimethylsilanol using HPLC method in accordance with OECD 117 test method. The result was disregarded because some necessary corrective adjustments that would be needed to validly interpret the result were not conducted. In a non-standard study, dimensionless coefficients of air/water (K_aw), octanol/air (K_oa) and octanol/water partition (K_ow) of trimethylsilanol were determined using a custom-made glass apparatus. The apparatus allowed for the establishment of octanol/air/water three phase equilibrium at a temperature range of 5 -35°C. Measured values of log K_ow = 1.22 ± 0.13, log K_aw = -2.77 ± 0.10 and log K_oa = 4.01 ± 0.04 and 25± 0.3°C were obtained for trimethylsilanol.