N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane

Hydrolysis

Description of key information

Hydrolysis half-life (silazane group): <1 minute at pH 4, pH 7 and pH 9 and 25°C (measured)

Hydrolysis half-life (diethoxy group): 0.4 hours at pH 4, 0.4 hours at pH 5, 10 hours at pH 7 and 0.2 hours at pH 9 at 20 - 25°C (QSAR)

Key value for chemical safety assessment

Half-life for hydrolysis:

1 min

at the temperature of:

25 °C

Additional information

The submission substance, N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane has two types of hydrolysable group; one silazane (Si-N-Si) and two ethoxy (-OCH₂CH₃) groups.

The silazane group is expected to hydrolyse very rapidly (instantaneously) in contact with water. This assumption is supported by a preliminary hydrolysis study conducted on the submission substance using a modified method in accordance with OECD 111/EC C.7. During the study, water at each pH was spiked with a known amount of the test substance and duplicate test solutions were prepared at each pH value. The diluted test solutions and blank were analysed using GC-FID; each sample was shaken, sampled and analysis was performed immediately at t=0 hours after fortification with the spiking solution. No peaks at the characteristic retention time of the test substance were observed in the GC chromatograms at time t=0 hours.

Also, an attempt was made to conduct a water solubility study for the submission substance using a modified method comparable to OECD Test Guideline 105 and in compliance with GLP (Young 2003). 100 mL water at 20°C was spiked with a solution of the test substance in 100 mL acetone, the solution was shaken, wrapped in aluminium foil to exclude light and sampled prior to placing in a water bath at 20°C. Duplicate samples were performed. Sampling of the test substance was performed at various time intervals of 0, 0.5 and 1 hour for test 1 and 0 hour only for test 2. Sample analysis was performed immediately after preparation using GC-FID. At t=0 h, t=0.5 h and t=1 h solutions, no peaks at the characteristic retention time of the test substance were observed in the chromatograms of the sample solution. This indicate that the test substance undergoes very rapid hydrolysis when in contact with water.

 

The silazane (Si-N-Si) group in contact with water undergoes instantaneous hydrolysis to form an intermediate hydrolysis product of 3-(diethoxy(methyl)silyl)propylamine and trimethylsilanol.

 

The hydrolysis half-lives of the intermediate hydrolysis product, 3-(diethoxy(methyl)silyl)propylamine have been determined using a validated QSAR estimation method. Hydrolysis half-life values of 0.4 hours at pH 4, 0.4 hours at pH 5, 10 hours at pH 7 and 0.2 hours at pH 9 and 20 -25°C were obtained for the intermediate hydrolysis product.

 

The products of hydrolysis of 3-(diethoxymethylsilyl)propylamine are 3-(dihydroxymethylsilyl)propylamine and ethanol.

Therefore, the ultimate hydrolysis products of the submission substance are trimethylsilanol, 3-(dihydroxymethylsilyl)propylamine and ethanol.