Diethoxy(methyl)silane

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

26 Feb 2015

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

GLP compliance:

not specified

Remarks:

Inhouse study conducted in order to determine the stability of the substance

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals for the parent/transformation products: Every 10 to 40 sec a 1H NMR spectrum was acquired after the tubes were transferred into the spectrometer.
- Sample storage conditions before analysis: 1H-NMR measurements were started immediately after mixing the sample and transferring the sample tube into the spectrometer (approx. 2 min)

Buffers:

- pH: 4
- Composition of buffer: CertiPur, Citric acid + hydrochloric acid + sodium hydroxide

- pH: 7
- Composition of buffer: Baker Analyzed, Potassium dihydrogen phosphate + disodiumhydrogen phosphate

- pH: 9
- Composition of buffer: CertiPur, Boronic acid + potassium chloride + sodium hydroxide

Details on test conditions:

TEST MEDIUM
- Preparation of test medium: deuterated water / 3-trimethylsilylpropionic acid, sodium salt, 2,2,3,3-tetradeuterated (Na-TSP-d4) (5006.46 mg D2O + 21.53 mg Na-TSP-d4)
- Kind and purity of water: deuterated water

Duration:

1 h

pH:

4

Temp.:

25 °C

Duration:

1 h

pH:

7

Temp.:

25 °C

Duration:

1 h

pH:

9

Temp.:

25 °C

Transformation products:

yes

No.:

#1

Details on hydrolysis and appearance of transformation product(s):

At all pH values only signals of ethanol could be observed after the first measurement. There were no signals of ethoxysilane detectable. Therefore it was concluded that hydrolysis was already completed when the first spectrum was measured.

pH:

4

Temp.:

25 °C

DT50:

< 2 min

Type:

not specified

pH:

7

Temp.:

25 °C

DT50:

< 2 min

Type:

not specified

pH:

9

Temp.:

25 °C

DT50:

< 2 min

Type:

not specified

At all pH values only signals of ethanol could be observed after the first measurement. No signals of ethoxysilane could be detected. Thus it was concluded that hydrolysis was already completed when the first spectrum was measured (about 2 min after mixing the test sample) and no exact half-life time or reaction rate could be calculated.

Independently from the hydrolysis reaction a fast decomposition of the Si-H bond was observed. At pH = 4, SiH-containing compounds were well detectable in the first spectra (by a SiMe signal split into a doublet; the SiH-signal itself is hidden by the water peak) and vanished within about 30 min. At pH = 7 and pH = 9, no SiH-containing compounds were detectable from the beginning. This known decomposition reaction comprises the splitting of the Si-H bond by water into siloxanes and molecular hydrogen. At pH = 7 and pH = 9, this hydrogen was observed as gas bubbles in the solution. Accordingly, the corresponding spectra feature broad signals and a low signal-to-noise ratio.

Validity criteria fulfilled:

not specified

Conclusions:

Diethoxy(methyl)silane CAS 2031-62-1 hydrolysis in less than 2 min at pH 4-9 and 25 °C as identified by 1H-NMR spectroscopy.

Description of key information

Diethoxy(methyl)silane: hydrolysis half-life < 2 min at 25°C and pH 7

Key value for chemical safety assessment

Half-life for hydrolysis:

2 min

at the temperature of:

25 °C

Additional information

One study is available testing the hydrolysis rate of diethoxy(methyl)silane (CAS 2031-62-1) (2015). The study was conducted according to EU Method C.7 and the hydrolysis rate was identified via 1H-NMR Spectroscopy. The hydrolysis was evaluated at pH 4, 7 and 9 and it was found that the substance hydrolysis in all cases in less than 2 min. The substance is known to stepwisely hydrolyse to the silanol hydrolysis products methylsilanediol followed by methylsilanetriol depending on pH. At pH 7 and 9, neither signals of ethoxysilane nor SiH-containing compounds were detectable from the beginning of the measurements showing that the final silanol hydrolysis product methylsilanetriol emerged immediately. At pH 4 no ethoxysilane signals could be detected at the beginning of the measurement while SiH-containing compounds were detectable in the first spectra and vanished within about 30 min indicating that formation of methylsilanetriol is slower.

The results show that, hydrolysis contributes significantly to the primary degradation of the substance in the environment.