N-[3-(trimethoxysilyl)propyl]aniline

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

(Q)SAR

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification

Principles of method if other than guideline:

The result was obtained using an appropriate QSAR method (see attached QMRF and QPRF for details).

Transformation products:

yes

No.:

#1

No.:

#2

pH:

7

DT50:

3.7 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: 20-25 °C

pH:

4

DT50:

0.2 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: 20-25 °C

pH:

5

DT50:

0.3 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: 20-25 °C

pH:

9

DT50:

0.1 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: 20-25 °C

Conclusions:

A hydrolysis half-life of approximately 3.7 hours at 20-25°C and pH 7 was predicted.

Description of key information

N-[3-(trimethoxysilyl)propyl]aniline CAS 3068-76-6: hydrolysis half-life = 3.7 h at 20-25°C and pH 7 (QSAR)

Key value for chemical safety assessment

Half-life for hydrolysis:

3.7 h

Additional information

Once released into the water phase, hydrolysis contributes significantly to the degradation of this substance. A QSAR that was developed by Peter Fisk Associates predicts half-lives at 20-25 °C of 0.2 h at pH 4, 0.3 h at pH 5, 3.7 h at pH 7 and 0.1 h at pH 9. Since the hydrolysis reaction may be acid or base catalysed, the rate of reaction is expected to be slowest at pH 7 and increase with pH increase or decrease.

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.

k_obs= k₀+ k_H3O+[H₃O⁺] + k_OH-[OH^-] + k_a[acid] + k_b[base]

At extreme pH values 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. This is supported by studies for various organosilicon compounds in which calculation of k_H3O+and k_OH-from the experimental results at pH 4 and 9, respectively, resulted in reasonable estimates of the half-life at pH 7.

Therefore, at low pH:

k_obs˜k_H3O+[H₃O⁺]

At pH 4 [H3O+]=10^-4mol dm^-3and at pH2 [H3O+]=10^-2mol dm^-3; therefore, k_obsat pH 2 should be approximately 100 times greater than k_obsat pH 4.

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

t_1/2(pH 2) = t_1/2(pH 4) / 100

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) x e^(0.08.(T-X))

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

Based on the predicted results of the model it is concluded that the substance will hydrolyse rapidly under environmentally conditions. The initial hydrolysis products are N-[3-(trihydroxysilyl)propyl]aniline and methanol.

Reference:

Mabey W. & Mill T. (1978). Critical review of hydrolysis of organic compounds in water under environmental conditions. J Phys Chem Ref Data. 7(2): 383-415.