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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
13 Feb - 05 Mar 2008
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Version / remarks:
2004
Qualifier:
according to guideline
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Version / remarks:
1992
GLP compliance:
yes
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
- Sampling method: Before and after incubation, 1 mL of the test sample solution was diluted with 2 mL of acetone and filtered (0.2 μm nylon filter). 1 μL aliquots of the test solutions at each pH value were analysed by measuring the FID signal of Dimethoxydimethylsilane after GC separation of the injected sample solution.
Buffers:
Buffer Solution pH 4.0
- pH: 4
- Composition of buffer: Biphthalate buffer, pH 4.00 ± 0.02 (25 °C), J.T. Baker, Art. No. 5657

Buffer Solution pH 7.0
- pH: 7
- Composition of buffer:Phosphate buffer, pH 7.00 ± 0.02 (25 °C), J.T. Baker, Art. No. 5656

Buffer Solution pH 9.0
- pH: 9
- Composition of buffer: Borate/Potassium chloride/NaOH buffer, pH 9.00 ± 0.02 (20 °C), J.T. Baker, Art. No. 7145


Nitrogen was passed through the buffer solutions for 1 min.
Details on test conditions:
TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: All glassware, which must be inert in the pH range applied, was rinsed with sterile buffer. The hydrolysis was carried out in flasks, which were stoppered or sealed with an inert material (e. g. glass).
- Sterilisation method: The buffer solutions were sterilized for 25 min in an autoclave prior to first use.
- If no traps were used, is the test system closed/open?: Test system is closed.
- Is there any indication of the test material adsorbing to the walls of the test apparatus?: No

TEST MEDIUM
- Volume used/treatment: 50 mL
- Kind and purity of water: Commercial buffer solutions
- Preparation of test medium: The test item was dissolved in 1 mL of acetone, filled up with 50 mL of buffer solution and treated in an aultrasonic bath for 1 min. Afterwards the solutions were filtered (0.2 µm nylon filter). To obtain a test solution of not more than half the water solubility, 25 mL of these solutions were diluted with buffer solution to obtain a volume of 50 mL.
- Identity of co-solvent: acetone
Duration:
120 h
pH:
4
Temp.:
50 °C
Initial conc. measured:
0 other: µg/mL
Duration:
3.85 h
pH:
7
Temp.:
25 °C
Initial conc. measured:
>= 343.868 - <= 389.596 other: µg/mL
Duration:
1.65 h
pH:
9
Temp.:
25 °C
Initial conc. measured:
>= 33.243 - <= 34.439 other: µg/mL
Number of replicates:
Duplicate
Positive controls:
no
Negative controls:
no
Preliminary study:
The results of pH 4.0 at 50 °C: no test item could be detected not even directly after preparation of the samples.
The results of pH 7.0 and pH 9.0 showed a significant degradation of Dimethoxydimethylsilane at 50 °C.
Transformation products:
yes
Remarks:
Transformation products were not specifically analysed in the study.
No.:
#1
No.:
#2
pH:
4
Temp.:
50 °C
Remarks on result:
not determinable because of methodological limitations
pH:
7
Temp.:
25 °C
DT50:
< 0.6 h
Type:
(pseudo-)first order (= half-life)
pH:
9
Temp.:
25 °C
DT50:
< 0.6 h
Type:
(pseudo-)first order (= half-life)
Details on results:
TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes

The hydrolysis of the test item was performed at 50.0 °C ± 0.1 °C at each of pH 4.0, pH 7.0 and pH 9.0 in a preliminary test. The solubility of Dimethoxydimethylsilane in buffers was very low. Thus, a solubilizer (acetone) was used. The solubility of Dimethoxydimethylsilane in buffer pH 4.0 was very low in spite of the solubilizer, no test item could be detected not even directly after preparation of the samples. Therefore, no further test according to the guideline could be performed. For pH 7.0 and pH 9.0 a main test at 25 °C was performed in order to calculate the hydrolytic half-life.

Table 1: Results of hydroylsis at pH 4.0 and 50 °C

Sample No. 1

Sample No. 2

Time [h]

Concentration measured [µg/mL]

Time [h]

Concentration measured [µg/mL]

0.00

0.00

0.00

0.00

0.55

0.00

0.55

0.00

2.4

0.00

2.4

0.00

120

0.00

120

0.00

 

Table 2: Results of hydrolysis at pH 7.0 and 25 °C

 

Sample No. 1

Sample No. 2

Time [h]

Concentration measured [µg/mL]

Hydrolysis [%]

Concentration measured [µg/mL]

Hydrolysis [%]

0.00

343.868

0

389.596

0

0.55

150.701

56

168.159

57

1.10

53.538

84

61.708

84

1.65

22.048

94

24.287

94

2.20

9.931

97

9.521

98

2.75

4.461

99

4.028

99

3.30

0.000

100

0.000

100

3.85

0.000

100

0.000

100

 

Table 3: Results of hydrolysis at pH 9.0 and 25 °C

 

Sample No. 1

Sample No. 2

Time [h]

Concentration measured [µg/mL]

Hydrolysis [%]

Concentration measured [µg/mL]

Hydrolysis [%]

0.00

34.439

0

33.243

0

0.55

0.000

100

0.000

100

1.10

0.000

100

0.000

100

1.65

0.000

100

0.000

100

Validity criteria fulfilled:
not applicable
Remarks:
No validity criteria specified in the OECD guideline.
Conclusions:
Hydrolysis half-lifes of < 0.6 h at pH 7 and 9 and 25 °C were determined in a study conducted according to OECD 111. The study is considered reliable.

Description of key information

Half-life: less than 0.6 hours

Key value for chemical safety assessment

Additional information

One guideline study investigating the hydrolysis of dimethoxydimethylsilane (CAS 1112-39-6) is available. The study was performed according to OECD 111 (GLP). First a preliminary study was conducted at pH 4, 7 and 9 at 50 °C for 120 h. Dimethoxydimethylsilane was found to be hydrolytically unstable at pH 7 and pH 9. At pH 4 the substance could not be analytically determined by GC/FID analysis. This could either be caused by immediate hydrolysis after addition to the buffer solution or due to analytical limitations. Based on this result a main test was only performed at pH 7 and pH 9 at 25 °C. The test duration for the main test was 3.85 h for pH 7 and 1.65 h for pH 9. For pH 7 and pH 9, the half-life time was determined to be less than 0.6 h at 25 °C. Therefore, it can be concluded that the dimethoxydimethylsilane will hydrolyse rapidly under environmentally relevant conditions. The formation of hydrolysis products was not measured in this study but based on the chemical structure of the substance dimethylsilanediol (1 mole, CAS 1066-42-8) and methanol (2 moles) are the expected hydrolysis products.