Registration Dossier

Environmental fate & pathways

Hydrolysis

Currently viewing:

Administrative data

Link to relevant study record(s)

Description of key information

Hydrolysis half-life: <3 min at pH 4,  357 min at pH 7 and 17 min at pH 9 at 20 - 25°C (measured data)

Key value for chemical safety assessment

Half-life for hydrolysis:
6 h

Additional information

Hydrolysis half-lives of <3 min at pH 4, 357 min at pH 7 and 17 min at pH 9 were determined at room temperature in a non-guideline study conducted according to a generally accepted scientific principle, but not in compliance with GLP. The result is considered to be reliable and selected as key study.

For an acid-base catalysed reaction in buffered solution, the measured rate constant is a linear combination of terms describing contributions from the uncatalyzed reaction as well as catalysis by hydronium, hydroxide, and general acids or bases.

kobs= k0+ kH3O+[H3O+] + kOH-[OH-] + ka[acid] + kb[base]

At extremes of pH and under standard hydrolysis test conditions, it is reasonable to suggest that the rate of hydrolysis is dominated by either the hydronium or hydroxide catalysed mechanism.

Therefore, at low pH:

kobskH3O+[H3O+]

At pH 4 [H3O+] =10-4mol dm-3and at pH 2 [H3O+] =10-2mol dm-3; therefore, kobs at pH 2 should be approximately 100 times greater than kobs at pH 4.

The half-life of a substance at pH 2 is calculated based on:

t1/2(pH 2) = t1/2(pH 4) / 100

The calculated half-life of 3-(diethoxymethylsilyl)propylamine at pH 2 is therefore <0.03 minutes (1.8 seconds). However, it is likely that factors such as diffusion become rate-determining when the half-life is less than 5-10 seconds. As a worst-case it can therefore be considered that the half-life for 3-(diethoxymethylsilyl)propylamine at pH 2 and 20-25°C is approximately 5 seconds.

Reaction rate increases with temperature therefore hydrolysis will be faster at physiologically relevant temperatures compared to standard laboratory conditions. Under ideal conditions, hydrolysis rate can be recalculated according to the equation:

DT50(XºC) = DT50(T) * e(0.08.(T-X))

Where T = temperature for which data are available and X = target temperature.

Thus, for 3-(diethoxymethylsilyl)propylamine the hydrolysis half-life at 37.5ºC and pH 7 (relevant for lungs and blood) is approximately 2.2 hours. At 37.5ºC and pH 2 (relevant for conditions in the stomach following oral exposure), it is not appropriate to apply any further correction for temperature to the limit value and the hydrolysis half-life is therefore approximately 5 seconds.

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

Hydrolysis of the read-across substance 3-aminopropyltriethoxysilane (CAS 919-30-2)

Data for the substance3-aminopropyltriethoxysilane(CAS 919-30-2) are read-across to the submission substance 3-(diethoxymethylsilyl)propylamine for appropriate endpoints.The presence of common functional group (3-aminopropyl), hydrolysis half-life and silanol hydrolysis product of the two substances is relevant to this read-across, as discussed in the appropriate Sections of the CSR for each endpoint.

For 3-aminopropyltriethoxysilane, hydrolysis half-lives at 24.7°C of 0.8 h at pH 5, 8.5 h at pH 7 and 0.15 h at pH 9 were determined in accordance with OECD 111 (Kozerski G E 2001). At pH 4, the substance has a predicted half-life of 0.4 h at 25°C.

The half-lives at pH 2 and 25°C, at pH 7 and 37.5°C and at pH 2 and 37.5°C may be calculated in the same way as for the registration substance above. This gives a half-life of 0.004 h (14 seconds) at pH 2 and 25°C, and 3.1 h at pH 7 and 37.5°C. It is likely that factors such as diffusion become rate-determining when the half-life is less than 5-10 seconds. As a worst-case it can therefore be considered that the half-life for the substance at pH 2 and 37.5°C is approximately 5 seconds.

The hydrolysis products are 3-aminopropylsilanetriol and ethanol.

Hydrolysis of the read-across substance2,2-dimethyl-4-(trimethoxysilyl)butylamine (CAS 157923-74-5)

Data for the substance2,2-dimethyl-4-(trimethoxysilyl)butylamine(CAS 157923-74-5) are read-across to the submission substance 3-(diethoxymethylsilyl)propylamine for appropriate endpoints (see Section 1.4).The hydrolysis half-life and silanol hydrolysis product of the two substances is relevant to this read-across, as discussed in the appropriate Sections of the CSR for each endpoint.

For 2,2-dimethyl-4-(trimethoxysilyl)butylamine, hydrolysis half-lives at 25°C of 0.2 h at pH 4, 3.7 h at pH 7 and 0.1 h at pH 9 were determined using a validated QSAR estimation method. 

The hydrolysis products are 2,2-dimethyl-4-(trihydroxysilyl)butylamine and methanol.