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EC number: 239-311-3
CAS number: 15267-95-5
Half-life 2.5 h at pH 7, QSAR, RL2
A half-life value of approximately 2.5 h at 20-25°C
and pH 7 was obtained using an accepted validated QSAR method (Peter
Fisk Associates, 2013a). The result is considered to be reliable and has
been assigned as key study.
A QSAR that is currently being developed
(Peter Fisk Associates, 2013b) predicts half-lives at 20-25°C of 0.2 h
at pH 4 and 0.3 at pH 5 and 0.1 at pH 9. As the hydrolysis reaction may
be acid or base catalysed, the rate of reaction is expected to be
slowest at pH 7 and increase as the pH is raised or lowered.
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. This is supported by studies for various organosilicon
compounds in which calculation of kH3O+and kOH-from
the experimental results at pH 4 and 9, respectively, resulted in
reasonable estimates of the half-life at pH 7 (Peter Fisk Associates,
Therefore, at low pH:
At pH 4 [H3O+]=10-4mol
dm-3and at pH2 [H3O+]=10-2mol
dm-3; therefore, kobsat pH 2 should be
approximately 100 times greater than kobsat pH 4.
The half-life of a substance at pH 2 is
calculated based on:
t1/2(pH 2) = t1/2(pH 4)
The calculated half-life of(chloromethyl)triethoxysilane
at pH 2 is therefore 5 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(chloromethyl)triethoxysilaneat
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
DT50(XºC) = DT50(T)
x e(0.08* (T-X))
Where T = temperature for which data are
available and X = target temperature.
hydrolysis half-life 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 hydrolysis products arechloromethylsilanetrioland
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